drm/amd/display: Try RGB before YCbCr 4:4:4 in stream validationgrafted

amdgpu_dm_create_validate_stream_for_sink() walks encoding_order[] and
uses the first encoding that validates. YCbCr 4:4:4 is listed before
RGB, so an HDMI sink that advertises 4:4:4 gets YCbCr 4:4:4 whenever the
"color format" property is left at AUTO, even though RGB fits the same
link.

That contradicts the documented AUTO behaviour for HDMI in enum
drm_connector_color_format (RGB, falling back to YCbCr 4:2:0 only when
the bandwidth is not available or the mode is 4:2:0-only), which the
amdgpu implementation of the property also describes. It also leaves
the "Broadcast RGB" property without effect on such sinks, since the
quantization range it selects only applies to RGB output.

Try RGB first. The mask still holds every encoding the sink supports,
so a mode that cannot carry RGB falls back exactly as before.

For reference, v7.2 picked RGB here unless YCbCr 4:4:4 was forced
through debugfs, while earlier kernels picked YCbCr 4:4:4 for any HDMI
sink that advertised it.

Fixes: 0b0ff65d3ca1 ("drm/amd/display: Refactor stream validation")
Suggested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Assisted-by: Claude Code:claude-fable-5-1
Signed-off-by: Adrian Betschart <adrian.betschart@cinemaone.ch>
Reviewed-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Adolfo Rodrigues <adolfotregosa@gmail.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7de432bc753133764dc40d37f9388da56de251e7)

17 files changed, 5177 insertions, 0 deletions

diff --git a/Documentation/kbuild/Kconfig.recursion-issue-01 b/Documentation/kbuild/Kconfig.recursion-issue-01
new file mode 100644
index 000000000..ac49836d8
--- /dev/null
+++ b/Documentation/kbuild/Kconfig.recursion-issue-01
@@ -0,0 +1,57 @@
+# Simple Kconfig recursive issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+# Test with:
+#
+# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
+#
+# This Kconfig file has a simple recursive dependency issue. In order to
+# understand why this recursive dependency issue occurs lets consider what
+# Kconfig needs to address. We iterate over what Kconfig needs to address
+# by stepping through the questions it needs to address sequentially.
+#
+#  * What values are possible for CORE?
+#
+# CORE_BELL_A_ADVANCED selects CORE, which means that it influences the values
+# that are possible for CORE. So for example if CORE_BELL_A_ADVANCED is 'y',
+# CORE must be 'y' too.
+#
+#  * What influences CORE_BELL_A_ADVANCED?
+#
+# As the name implies CORE_BELL_A_ADVANCED is an advanced feature of
+# CORE_BELL_A so naturally it depends on CORE_BELL_A. So if CORE_BELL_A is 'y'
+# we know CORE_BELL_A_ADVANCED can be 'y' too.
+#
+#   * What influences CORE_BELL_A?
+#
+# CORE_BELL_A depends on CORE, so CORE influences CORE_BELL_A.
+#
+# But that is a problem, because this means that in order to determine
+# what values are possible for CORE we ended up needing to address questions
+# regarding possible values of CORE itself again. Answering the original
+# question of what are the possible values of CORE would make the kconfig
+# tools run in a loop. When this happens Kconfig exits and complains about
+# the "recursive dependency detected" error.
+#
+# Reading the Documentation/kbuild/Kconfig.recursion-issue-01 file it may be
+# obvious that an easy solution to this problem should just be the removal
+# of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
+# since CORE_BELL_A depends on CORE. Recursive dependency issues are not always
+# so trivial to resolve, we provide another example below of practical
+# implications of this recursive issue where the solution is perhaps not so
+# easy to understand. Note that matching semantics on the dependency on
+# CORE also consist of a solution to this recursive problem.
+
+mainmenu "Simple example to demo kconfig recursive dependency issue"
+
+config CORE
+	tristate
+
+config CORE_BELL_A
+	tristate
+	depends on CORE
+
+config CORE_BELL_A_ADVANCED
+	tristate
+	depends on CORE_BELL_A
+	select CORE
diff --git a/Documentation/kbuild/Kconfig.recursion-issue-02 b/Documentation/kbuild/Kconfig.recursion-issue-02
new file mode 100644
index 000000000..09dcb92d9
--- /dev/null
+++ b/Documentation/kbuild/Kconfig.recursion-issue-02
@@ -0,0 +1,63 @@
+# Cumulative Kconfig recursive issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+# Test with:
+#
+# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
+#
+# The recursive limitations with Kconfig has some non intuitive implications on
+# kconfig semantics which are documented here. One known practical implication
+# of the recursive limitation is that drivers cannot negate features from other
+# drivers if they share a common core requirement and use disjoint semantics to
+# annotate those requirements, ie, some drivers use "depends on" while others
+# use "select". For instance it means if a driver A and driver B share the same
+# core requirement, and one uses "select" while the other uses "depends on" to
+# annotate this, all features that driver A selects cannot now be negated by
+# driver B.
+#
+# A perhaps not so obvious implication of this is that, if semantics on these
+# core requirements are not carefully synced, as drivers evolve features
+# they select or depend on end up becoming shared requirements which cannot be
+# negated by other drivers.
+#
+# The example provided in Documentation/kbuild/Kconfig.recursion-issue-02
+# describes a simple driver core layout of example features a kernel might
+# have. Let's assume we have some CORE functionality, then the kernel has a
+# series of bells and whistles it desires to implement, its not so advanced so
+# it only supports bells at this time: CORE_BELL_A and CORE_BELL_B. If
+# CORE_BELL_A has some advanced feature CORE_BELL_A_ADVANCED which selects
+# CORE_BELL_A then CORE_BELL_A ends up becoming a common BELL feature which
+# other bells in the system cannot negate. The reason for this issue is
+# due to the disjoint use of semantics on expressing each bell's relationship
+# with CORE, one uses "depends on" while the other uses "select". Another
+# more important reason is that kconfig does not check for dependencies listed
+# under 'select' for a symbol, when such symbols are selected kconfig them
+# as mandatory required symbols. For more details on the heavy handed nature
+# of select refer to Documentation/kbuild/Kconfig.select-break
+#
+# To fix this the "depends on CORE" must be changed to "select CORE", or the
+# "select CORE" must be changed to "depends on CORE".
+#
+# For an example real world scenario issue refer to the attempt to remove
+# "select FW_LOADER" [0], in the end the simple alternative solution to this
+# problem consisted on matching semantics with newly introduced features.
+#
+# [0] https://lore.kernel.org/r/1432241149-8762-1-git-send-email-mcgrof@do-not-panic.com
+
+mainmenu "Simple example to demo cumulative kconfig recursive dependency implication"
+
+config CORE
+	tristate
+
+config CORE_BELL_A
+	tristate
+	depends on CORE
+
+config CORE_BELL_A_ADVANCED
+	tristate
+	select CORE_BELL_A
+
+config CORE_BELL_B
+	tristate
+	depends on !CORE_BELL_A
+	select CORE
diff --git a/Documentation/kbuild/Kconfig.select-break b/Documentation/kbuild/Kconfig.select-break
new file mode 100644
index 000000000..365ceb342
--- /dev/null
+++ b/Documentation/kbuild/Kconfig.select-break
@@ -0,0 +1,33 @@
+# Select broken dependency issue
+# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#
+# Test with:
+#
+# make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.select-break menuconfig
+#
+# kconfig will not complain and enable this layout for configuration. This is
+# currently a feature of kconfig, given select was designed to be heavy handed.
+# Kconfig currently does not check the list of symbols listed on a symbol's
+# "select" list, this is done on purpose to help load a set of known required
+# symbols. Because of this use of select should be used with caution. An
+# example of this issue is below.
+#
+# The option B and C are clearly contradicting with respect to A.
+# However, when A is set, C can be set as well because Kconfig does not
+# visit the dependencies of the select target (in this case B).  And since
+# Kconfig does not visit the dependencies, it breaks the dependencies of B
+# (!A).
+
+mainmenu "Simple example to demo kconfig select broken dependency issue"
+
+config A
+	bool "CONFIG A"
+
+config B
+	bool "CONFIG B"
+	depends on !A
+
+config C
+	bool "CONFIG C"
+	depends on A
+	select B
diff --git a/Documentation/kbuild/bash-completion.rst b/Documentation/kbuild/bash-completion.rst
new file mode 100644
index 000000000..2b52dbcd0
--- /dev/null
+++ b/Documentation/kbuild/bash-completion.rst
@@ -0,0 +1,65 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+
+==========================
+Bash completion for Kbuild
+==========================
+
+The kernel build system is written using Makefiles, and Bash completion
+for the `make` command is available through the `bash-completion`_ project.
+
+However, the Makefiles for the kernel build are complex. The generic completion
+rules for the `make` command do not provide meaningful suggestions for the
+kernel build system, except for the options of the `make` command itself.
+
+To enhance completion for various variables and targets, the kernel source
+includes its own completion script at `scripts/bash-completion/make`.
+
+This script provides additional completions when working within the kernel tree.
+Outside the kernel tree, it defaults to the generic completion rules for the
+`make` command.
+
+Prerequisites
+=============
+
+The script relies on helper functions provided by `bash-completion`_ project.
+Please ensure it is installed on your system. On most distributions, you can
+install the `bash-completion` package through the standard package manager.
+
+How to use
+==========
+
+You can source the script directly::
+
+  $ source scripts/bash-completion/make
+
+Or, you can copy it into the search path for Bash completion scripts.
+For example::
+
+  $ mkdir -p ~/.local/share/bash-completion/completions
+  $ cp scripts/bash-completion/make ~/.local/share/bash-completion/completions/
+
+Details
+=======
+
+The additional completion for Kbuild is enabled in the following cases:
+
+ - You are in the root directory of the kernel source.
+ - You are in the top-level build directory created by the O= option
+   (checked via the `source` symlink pointing to the kernel source).
+ - The -C make option specifies the kernel source or build directory.
+ - The -f make option specifies a file in the kernel source or build directory.
+
+If none of the above are met, it falls back to the generic completion rules.
+
+The completion supports:
+
+  - Commonly used targets, such as `all`, `menuconfig`, `dtbs`, etc.
+  - Make (or environment) variables, such as `ARCH`, `LLVM`, etc.
+  - Single-target builds (`foo/bar/baz.o`)
+  - Configuration files (`*_defconfig` and `*.config`)
+
+Some variables offer intelligent behavior. For instance, `CROSS_COMPILE=`
+followed by a TAB displays installed toolchains. The list of defconfig files
+shown depends on the value of the `ARCH=` variable.
+
+.. _bash-completion: https://github.com/scop/bash-completion/
diff --git a/Documentation/kbuild/gcc-plugins.rst b/Documentation/kbuild/gcc-plugins.rst
new file mode 100644
index 000000000..c578c6ba3
--- /dev/null
+++ b/Documentation/kbuild/gcc-plugins.rst
@@ -0,0 +1,133 @@
+=========================
+GCC plugin infrastructure
+=========================
+
+
+Introduction
+============
+
+GCC plugins are loadable modules that provide extra features to the
+compiler [1]_. They are useful for runtime instrumentation and static analysis.
+We can analyse, change and add further code during compilation via
+callbacks [2]_, GIMPLE [3]_, IPA [4]_ and RTL passes [5]_.
+
+The GCC plugin infrastructure of the kernel supports building out-of-tree
+modules, cross-compilation and building in a separate directory.
+Plugin source files have to be compilable by a C++ compiler.
+
+Currently the GCC plugin infrastructure supports only some architectures.
+Grep "select HAVE_GCC_PLUGINS" to find out which architectures support
+GCC plugins.
+
+This infrastructure was ported from grsecurity [6]_ and PaX [7]_.
+
+--
+
+.. [1] https://gcc.gnu.org/onlinedocs/gccint/Plugins.html
+.. [2] https://gcc.gnu.org/onlinedocs/gccint/Plugin-API.html#Plugin-API
+.. [3] https://gcc.gnu.org/onlinedocs/gccint/GIMPLE.html
+.. [4] https://gcc.gnu.org/onlinedocs/gccint/IPA.html
+.. [5] https://gcc.gnu.org/onlinedocs/gccint/RTL.html
+.. [6] https://grsecurity.net/
+.. [7] https://pax.grsecurity.net/
+
+
+Purpose
+=======
+
+GCC plugins are designed to provide a place to experiment with potential
+compiler features that are neither in GCC nor Clang upstream. Once
+their utility is proven, the goal is to upstream the feature into GCC
+(and Clang), and then to finally remove them from the kernel once the
+feature is available in all supported versions of GCC.
+
+Specifically, new plugins should implement only features that have no
+upstream compiler support (in either GCC or Clang).
+
+When a feature exists in Clang but not GCC, effort should be made to
+bring the feature to upstream GCC (rather than just as a kernel-specific
+GCC plugin), so the entire ecosystem can benefit from it.
+
+Similarly, even if a feature provided by a GCC plugin does *not* exist
+in Clang, but the feature is proven to be useful, effort should be spent
+to upstream the feature to GCC (and Clang).
+
+After a feature is available in upstream GCC, the plugin will be made
+unbuildable for the corresponding GCC version (and later). Once all
+kernel-supported versions of GCC provide the feature, the plugin will
+be removed from the kernel.
+
+
+Files
+=====
+
+**$(src)/scripts/gcc-plugins**
+
+	This is the directory of the GCC plugins.
+
+**$(src)/scripts/gcc-plugins/gcc-common.h**
+
+	This is a compatibility header for GCC plugins.
+	It should be always included instead of individual gcc headers.
+
+**$(src)/scripts/gcc-plugins/gcc-generate-gimple-pass.h,
+$(src)/scripts/gcc-plugins/gcc-generate-ipa-pass.h,
+$(src)/scripts/gcc-plugins/gcc-generate-simple_ipa-pass.h,
+$(src)/scripts/gcc-plugins/gcc-generate-rtl-pass.h**
+
+	These headers automatically generate the registration structures for
+	GIMPLE, SIMPLE_IPA, IPA and RTL passes.
+	They should be preferred to creating the structures by hand.
+
+
+Usage
+=====
+
+You must install the gcc plugin headers for your gcc version,
+e.g., on Ubuntu for gcc-10::
+
+	apt-get install gcc-10-plugin-dev
+
+Or on Fedora::
+
+	dnf install gcc-plugin-devel libmpc-devel
+
+Or on Fedora when using cross-compilers that include plugins::
+
+	dnf install libmpc-devel
+
+Enable the GCC plugin infrastructure and some plugin(s) you want to use
+in the kernel config::
+
+	CONFIG_GCC_PLUGINS=y
+	CONFIG_GCC_PLUGIN_LATENT_ENTROPY=y
+	...
+
+Run gcc (native or cross-compiler) to ensure plugin headers are detected::
+
+	gcc -print-file-name=plugin
+	CROSS_COMPILE=arm-linux-gnu- ${CROSS_COMPILE}gcc -print-file-name=plugin
+
+The word "plugin" means they are not detected::
+
+	plugin
+
+A full path means they are detected::
+
+       /usr/lib/gcc/x86_64-redhat-linux/12/plugin
+
+To compile the minimum tool set including the plugin(s)::
+
+	make scripts
+
+or just run the kernel make and compile the whole kernel with
+the cyclomatic complexity GCC plugin.
+
+
+4. How to add a new GCC plugin
+==============================
+
+The GCC plugins are in scripts/gcc-plugins/. You need to put plugin source files
+right under scripts/gcc-plugins/. Creating subdirectories is not supported.
+It must be added to scripts/gcc-plugins/Makefile, scripts/Makefile.gcc-plugins
+and a relevant Kconfig file.
diff --git a/Documentation/kbuild/gendwarfksyms.rst b/Documentation/kbuild/gendwarfksyms.rst
new file mode 100644
index 000000000..f1573dcc6
--- /dev/null
+++ b/Documentation/kbuild/gendwarfksyms.rst
@@ -0,0 +1,418 @@
+=======================
+DWARF module versioning
+=======================
+
+Introduction
+============
+
+When CONFIG_MODVERSIONS is enabled, symbol versions for modules
+are typically calculated from preprocessed source code using the
+**genksyms** tool.  However, this is incompatible with languages such
+as Rust, where the source code has insufficient information about
+the resulting ABI. With CONFIG_GENDWARFKSYMS (and CONFIG_DEBUG_INFO)
+selected, **gendwarfksyms** is used instead to calculate symbol versions
+from the DWARF debugging information, which contains the necessary
+details about the final module ABI.
+
+Dependencies
+------------
+
+gendwarfksyms depends on the libelf, libdw, and zlib libraries.
+
+Here are a few examples of how to install these dependencies:
+
+* Arch Linux and derivatives::
+
+	sudo pacman --needed -S libelf zlib
+
+* Debian, Ubuntu, and derivatives::
+
+	sudo apt install libelf-dev libdw-dev zlib1g-dev
+
+* Fedora and derivatives::
+
+	sudo dnf install elfutils-libelf-devel elfutils-devel zlib-devel
+
+* openSUSE and derivatives::
+
+	sudo zypper install libelf-devel libdw-devel zlib-devel
+
+Usage
+-----
+
+gendwarfksyms accepts a list of object files on the command line, and a
+list of symbol names (one per line) in standard input::
+
+	Usage: gendwarfksyms [options] elf-object-file ... < symbol-list
+
+	Options:
+	  -d, --debug          Print debugging information
+	      --dump-dies      Dump DWARF DIE contents
+	      --dump-die-map   Print debugging information about die_map changes
+	      --dump-types     Dump type strings
+	      --dump-versions  Dump expanded type strings used for symbol versions
+	  -s, --stable         Support kABI stability features
+	  -T, --symtypes file  Write a symtypes file
+	  -h, --help           Print this message
+
+
+Type information availability
+=============================
+
+While symbols are typically exported in the same translation unit (TU)
+where they're defined, it's also perfectly fine for a TU to export
+external symbols. For example, this is done when calculating symbol
+versions for exports in stand-alone assembly code.
+
+To ensure the compiler emits the necessary DWARF type information in the
+TU where symbols are actually exported, gendwarfksyms adds a pointer
+to exported symbols in the `EXPORT_SYMBOL()` macro using the following
+macro::
+
+	#define __GENDWARFKSYMS_EXPORT(sym)				\
+		static typeof(sym) *__gendwarfksyms_ptr_##sym __used	\
+			__section(".discard.gendwarfksyms") = &sym;
+
+
+When a symbol pointer is found in DWARF, gendwarfksyms can use its
+type for calculating symbol versions even if the symbol is defined
+elsewhere. The name of the symbol pointer is expected to start with
+`__gendwarfksyms_ptr_`, followed by the name of the exported symbol.
+
+Symtypes output format
+======================
+
+Similarly to genksyms, gendwarfksyms supports writing a symtypes
+file for each processed object that contain types for exported
+symbols and each referenced type that was used in calculating symbol
+versions. These files can be useful when trying to determine what
+exactly caused symbol versions to change between builds. To generate
+symtypes files during a kernel build, set `KBUILD_SYMTYPES=1`.
+
+Matching the existing format, the first column of each line contains
+either a type reference or a symbol name. Type references have a
+one-letter prefix followed by "#" and the name of the type. Four
+reference types are supported::
+
+	e#<type> = enum
+	s#<type> = struct
+	t#<type> = typedef
+	u#<type> = union
+
+Type names with spaces in them are wrapped in single quotes, e.g.::
+
+	s#'core::result::Result<u8, core::num::error::ParseIntError>'
+
+The rest of the line contains a type string. Unlike with genksyms that
+produces C-style type strings, gendwarfksyms uses the same simple parsed
+DWARF format produced by **--dump-dies**, but with type references
+instead of fully expanded strings.
+
+Maintaining a stable kABI
+=========================
+
+Distribution maintainers often need the ability to make ABI compatible
+changes to kernel data structures due to LTS updates or backports. Using
+the traditional `#ifndef __GENKSYMS__` to hide these changes from symbol
+versioning won't work when processing object files. To support this
+use case, gendwarfksyms provides kABI stability features designed to
+hide changes that won't affect the ABI when calculating versions. These
+features are all gated behind the **--stable** command line flag and are
+not used in the mainline kernel. To use stable features during a kernel
+build, set `KBUILD_GENDWARFKSYMS_STABLE=1`.
+
+Examples for using these features are provided in the
+**scripts/gendwarfksyms/examples** directory, including helper macros
+for source code annotation. Note that as these features are only used to
+transform the inputs for symbol versioning, the user is responsible for
+ensuring that their changes actually won't break the ABI.
+
+kABI rules
+----------
+
+kABI rules allow distributions to fine-tune certain parts
+of gendwarfksyms output and thus control how symbol
+versions are calculated. These rules are defined in the
+`.discard.gendwarfksyms.kabi_rules` section of the object file and
+consist of simple null-terminated strings with the following structure::
+
+	version\0type\0target\0value\0
+
+This string sequence is repeated as many times as needed to express all
+the rules. The fields are as follows:
+
+- `version`: Ensures backward compatibility for future changes to the
+  structure. Currently expected to be "1".
+- `type`: Indicates the type of rule being applied.
+- `target`: Specifies the target of the rule, typically the fully
+  qualified name of the DWARF Debugging Information Entry (DIE).
+- `value`: Provides rule-specific data.
+
+The following helper macros, for example, can be used to specify rules
+in the source code::
+
+	#define ___KABI_RULE(hint, target, value)                            \
+		static const char __PASTE(__gendwarfksyms_rule_,             \
+					  __COUNTER__)[] __used __aligned(1) \
+			__section(".discard.gendwarfksyms.kabi_rules") =     \
+				"1\0" #hint "\0" target "\0" value
+
+	#define __KABI_RULE(hint, target, value) \
+		___KABI_RULE(hint, #target, #value)
+
+
+Currently, only the rules discussed in this section are supported, but
+the format is extensible enough to allow further rules to be added as
+need arises.
+
+Managing definition visibility
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A declaration can change into a full definition when additional includes
+are pulled into the translation unit. This changes the versions of any
+symbol that references the type even if the ABI remains unchanged. As
+it may not be possible to drop includes without breaking the build, the
+`declonly` rule can be used to specify a type as declaration-only, even
+if the debugging information contains the full definition.
+
+The rule fields are expected to be as follows:
+
+- `type`: "declonly"
+- `target`: The fully qualified name of the target data structure
+  (as shown in **--dump-dies** output).
+- `value`: This field is ignored.
+
+Using the `__KABI_RULE` macro, this rule can be defined as::
+
+	#define KABI_DECLONLY(fqn) __KABI_RULE(declonly, fqn, )
+
+Example usage::
+
+	struct s {
+		/* definition */
+	};
+
+	KABI_DECLONLY(s);
+
+Adding enumerators
+~~~~~~~~~~~~~~~~~~
+
+For enums, all enumerators and their values are included in calculating
+symbol versions, which becomes a problem if we later need to add more
+enumerators without changing symbol versions. The `enumerator_ignore`
+rule allows us to hide named enumerators from the input.
+
+The rule fields are expected to be as follows:
+
+- `type`: "enumerator_ignore"
+- `target`: The fully qualified name of the target enum
+  (as shown in **--dump-dies** output) and the name of the
+  enumerator field separated by a space.
+- `value`: This field is ignored.
+
+Using the `__KABI_RULE` macro, this rule can be defined as::
+
+	#define KABI_ENUMERATOR_IGNORE(fqn, field) \
+		__KABI_RULE(enumerator_ignore, fqn field, )
+
+Example usage::
+
+	enum e {
+		A, B, C, D,
+	};
+
+	KABI_ENUMERATOR_IGNORE(e, B);
+	KABI_ENUMERATOR_IGNORE(e, C);
+
+If the enum additionally includes an end marker and new values must
+be added in the middle, we may need to use the old value for the last
+enumerator when calculating versions. The `enumerator_value` rule allows
+us to override the value of an enumerator for version calculation:
+
+- `type`: "enumerator_value"
+- `target`: The fully qualified name of the target enum
+  (as shown in **--dump-dies** output) and the name of the
+  enumerator field separated by a space.
+- `value`: Integer value used for the field.
+
+Using the `__KABI_RULE` macro, this rule can be defined as::
+
+	#define KABI_ENUMERATOR_VALUE(fqn, field, value) \
+		__KABI_RULE(enumerator_value, fqn field, value)
+
+Example usage::
+
+	enum e {
+		A, B, C, LAST,
+	};
+
+	KABI_ENUMERATOR_IGNORE(e, C);
+	KABI_ENUMERATOR_VALUE(e, LAST, 2);
+
+Managing structure size changes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+A data structure can be partially opaque to modules if its allocation is
+handled by the core kernel, and modules only need to access some of its
+members. In this situation, it's possible to append new members to the
+structure without breaking the ABI, as long as the layout for the original
+members remains unchanged.
+
+To append new members, we can hide them from symbol versioning as
+described in section :ref:`Hiding members <hiding_members>`, but we can't
+hide the increase in structure size. The `byte_size` rule allows us to
+override the structure size used for symbol versioning.
+
+The rule fields are expected to be as follows:
+
+- `type`: "byte_size"
+- `target`: The fully qualified name of the target data structure
+  (as shown in **--dump-dies** output).
+- `value`: A positive decimal number indicating the structure size
+  in bytes.
+
+Using the `__KABI_RULE` macro, this rule can be defined as::
+
+	#define KABI_BYTE_SIZE(fqn, value) \
+		__KABI_RULE(byte_size, fqn, value)
+
+Example usage::
+
+	struct s {
+		/* Unchanged original members */
+		unsigned long a;
+		void *p;
+
+		/* Appended new members */
+		KABI_IGNORE(0, unsigned long n);
+	};
+
+	KABI_BYTE_SIZE(s, 16);
+
+Overriding type strings
+~~~~~~~~~~~~~~~~~~~~~~~
+
+In rare situations where distributions must make significant changes to
+otherwise opaque data structures that have inadvertently been included
+in the published ABI, keeping symbol versions stable using the more
+targeted kABI rules can become tedious. The `type_string` rule allows us
+to override the full type string for a type or a symbol, and even add
+types for versioning that no longer exist in the kernel.
+
+The rule fields are expected to be as follows:
+
+- `type`: "type_string"
+- `target`: The fully qualified name of the target data structure
+  (as shown in **--dump-dies** output) or symbol.
+- `value`: A valid type string (as shown in **--symtypes**) output)
+  to use instead of the real type.
+
+Using the `__KABI_RULE` macro, this rule can be defined as::
+
+	#define KABI_TYPE_STRING(type, str) \
+		___KABI_RULE("type_string", type, str)
+
+Example usage::
+
+	/* Override type for a structure */
+	KABI_TYPE_STRING("s#s",
+		"structure_type s { "
+			"member base_type int byte_size(4) "
+				"encoding(5) n "
+			"data_member_location(0) "
+		"} byte_size(8)");
+
+	/* Override type for a symbol */
+	KABI_TYPE_STRING("my_symbol", "variable s#s");
+
+The `type_string` rule should be used only as a last resort if maintaining
+a stable symbol versions cannot be reasonably achieved using other
+means. Overriding a type string increases the risk of actual ABI breakages
+going unnoticed as it hides all changes to the type.
+
+Adding structure members
+------------------------
+
+Perhaps the most common ABI compatible change is adding a member to a
+kernel data structure. When changes to a structure are anticipated,
+distribution maintainers can pre-emptively reserve space in the
+structure and take it into use later without breaking the ABI. If
+changes are needed to data structures without reserved space, existing
+alignment holes can potentially be used instead. While kABI rules could
+be added for these type of changes, using unions is typically a more
+natural method. This section describes gendwarfksyms support for using
+reserved space in data structures and hiding members that don't change
+the ABI when calculating symbol versions.
+
+Reserving space and replacing members
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Space is typically reserved for later use by appending integer types, or
+arrays, to the end of the data structure, but any type can be used. Each
+reserved member needs a unique name, but as the actual purpose is usually
+not known at the time the space is reserved, for convenience, names that
+start with `__kabi_` are left out when calculating symbol versions::
+
+	struct s {
+		long a;
+		long __kabi_reserved_0; /* reserved for future use */
+	};
+
+The reserved space can be taken into use by wrapping the member in a
+union, which includes the original type and the replacement member::
+
+	struct s {
+		long a;
+		union {
+			long __kabi_reserved_0; /* original type */
+			struct b b; /* replaced field */
+		};
+	};
+
+If the `__kabi_` naming scheme was used when reserving space, the name
+of the first member of the union must start with `__kabi_reserved`. This
+ensures the original type is used when calculating versions, but the name
+is again left out. The rest of the union is ignored.
+
+If we're replacing a member that doesn't follow this naming convention,
+we also need to preserve the original name to avoid changing versions,
+which we can do by changing the first union member's name to start with
+`__kabi_renamed` followed by the original name.
+
+The examples include `KABI_(RESERVE|USE|REPLACE)*` macros that help
+simplify the process and also ensure the replacement member is correctly
+aligned and its size won't exceed the reserved space.
+
+.. _hiding_members:
+
+Hiding members
+~~~~~~~~~~~~~~
+
+Predicting which structures will require changes during the support
+timeframe isn't always possible, in which case one might have to resort
+to placing new members into existing alignment holes::
+
+	struct s {
+		int a;
+		/* a 4-byte alignment hole */
+		unsigned long b;
+	};
+
+
+While this won't change the size of the data structure, one needs to
+be able to hide the added members from symbol versioning. Similarly
+to reserved fields, this can be accomplished by wrapping the added
+member to a union where one of the fields has a name starting with
+`__kabi_ignored`::
+
+	struct s {
+		int a;
+		union {
+			char __kabi_ignored_0;
+			int n;
+		};
+		unsigned long b;
+	};
+
+With **--stable**, both versions produce the same symbol version. The
+examples include a `KABI_IGNORE` macro to simplify the code.
diff --git a/Documentation/kbuild/headers_install.rst b/Documentation/kbuild/headers_install.rst
new file mode 100644
index 000000000..f6c6b74a6
--- /dev/null
+++ b/Documentation/kbuild/headers_install.rst
@@ -0,0 +1,44 @@
+=============================================
+Exporting kernel headers for use by userspace
+=============================================
+
+The "make headers_install" command exports the kernel's header files in a
+form suitable for use by userspace programs.
+
+The linux kernel's exported header files describe the API for user space
+programs attempting to use kernel services.  These kernel header files are
+used by the system's C library (such as glibc or uClibc) to define available
+system calls, as well as constants and structures to be used with these
+system calls.  The C library's header files include the kernel header files
+from the "linux" subdirectory.  The system's libc headers are usually
+installed at the default location /usr/include and the kernel headers in
+subdirectories under that (most notably /usr/include/linux and
+/usr/include/asm).
+
+Kernel headers are backwards compatible, but not forwards compatible.  This
+means that a program built against a C library using older kernel headers
+should run on a newer kernel (although it may not have access to new
+features), but a program built against newer kernel headers may not work on an
+older kernel.
+
+The "make headers_install" command can be run in the top level directory of the
+kernel source code (or using a standard out-of-tree build).  It takes two
+optional arguments::
+
+  make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr
+
+ARCH indicates which architecture to produce headers for, and defaults to the
+current architecture.  The linux/asm directory of the exported kernel headers
+is platform-specific, to see a complete list of supported architectures use
+the command::
+
+  ls -d include/asm-* | sed 's/.*-//'
+
+INSTALL_HDR_PATH indicates where to install the headers. It defaults to
+"./usr".
+
+An 'include' directory is automatically created inside INSTALL_HDR_PATH and
+headers are installed in 'INSTALL_HDR_PATH/include'.
+
+The kernel header export infrastructure is maintained by David Woodhouse
+<dwmw2@infradead.org>.
diff --git a/Documentation/kbuild/index.rst b/Documentation/kbuild/index.rst
new file mode 100644
index 000000000..f46233be8
--- /dev/null
+++ b/Documentation/kbuild/index.rst
@@ -0,0 +1,26 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+Kernel Build System
+===================
+
+.. toctree::
+    :maxdepth: 1
+
+    kconfig-language
+    kconfig-macro-language
+
+    kbuild
+    kconfig
+    makefiles
+    modules
+
+    headers_install
+
+    issues
+    reproducible-builds
+    gcc-plugins
+    llvm
+    gendwarfksyms
+
+    bash-completion
diff --git a/Documentation/kbuild/issues.rst b/Documentation/kbuild/issues.rst
new file mode 100644
index 000000000..bdab01f73
--- /dev/null
+++ b/Documentation/kbuild/issues.rst
@@ -0,0 +1,15 @@
+================
+Recursion issues
+================
+
+issue #1
+--------
+
+.. literalinclude:: Kconfig.recursion-issue-01
+   :language: kconfig
+
+issue #2
+--------
+
+.. literalinclude:: Kconfig.recursion-issue-02
+   :language: kconfig
diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
new file mode 100644
index 000000000..5a9013bac
--- /dev/null
+++ b/Documentation/kbuild/kbuild.rst
@@ -0,0 +1,349 @@
+======
+Kbuild
+======
+
+
+Output files
+============
+
+modules.order
+-------------
+This file records the order in which modules appear in Makefiles. This
+is used by modprobe to deterministically resolve aliases that match
+multiple modules.
+
+modules.builtin
+---------------
+This file lists all modules that are built into the kernel. This is used
+by modprobe to not fail when trying to load something builtin.
+
+modules.builtin.modinfo
+-----------------------
+This file contains modinfo from all modules that are built into the kernel.
+Unlike modinfo of a separate module, all fields are prefixed with module name.
+
+modules.builtin.ranges
+----------------------
+This file contains address offset ranges (per ELF section) for all modules
+that are built into the kernel. Together with System.map, it can be used
+to associate module names with symbols.
+
+Environment variables
+=====================
+
+KCPPFLAGS
+---------
+Additional options to pass when preprocessing. The preprocessing options
+will be used in all cases where kbuild does preprocessing including
+building C files and assembler files.
+
+KAFLAGS
+-------
+Additional options to the assembler (for built-in and modules).
+
+AFLAGS_MODULE
+-------------
+Additional assembler options for modules.
+
+AFLAGS_KERNEL
+-------------
+Additional assembler options for built-in.
+
+KCFLAGS
+-------
+Additional options to the C compiler (for built-in and modules).
+
+KRUSTFLAGS
+----------
+Additional options to the Rust compiler (for built-in and modules).
+
+CFLAGS_KERNEL
+-------------
+Additional options for $(CC) when used to compile
+code that is compiled as built-in.
+
+CFLAGS_MODULE
+-------------
+Additional module specific options to use for $(CC).
+
+RUSTFLAGS_KERNEL
+----------------
+Additional options for $(RUSTC) when used to compile
+code that is compiled as built-in.
+
+RUSTFLAGS_MODULE
+----------------
+Additional module specific options to use for $(RUSTC).
+
+LDFLAGS_MODULE
+--------------
+Additional options used for $(LD) when linking modules.
+
+HOSTCFLAGS
+----------
+Additional flags to be passed to $(HOSTCC) when building host programs.
+
+HOSTCXXFLAGS
+------------
+Additional flags to be passed to $(HOSTCXX) when building host programs.
+
+HOSTRUSTFLAGS
+-------------
+Additional flags to be passed to $(HOSTRUSTC) when building host programs.
+
+PROCMACROLDFLAGS
+----------------
+Flags to be passed when linking Rust proc macros. Since proc macros are loaded
+by rustc at build time, they must be linked in a way that is compatible with
+the rustc toolchain being used.
+
+For instance, it can be useful when rustc uses a different C library than
+the one the user wants to use for host programs.
+
+If unset, it defaults to the flags passed when linking host programs.
+
+HOSTLDFLAGS
+-----------
+Additional flags to be passed when linking host programs.
+
+HOSTLDLIBS
+----------
+Additional libraries to link against when building host programs.
+
+.. _userkbuildflags:
+
+USERCFLAGS
+----------
+Additional options used for $(CC) when compiling userprogs.
+
+USERLDFLAGS
+-----------
+Additional options used for $(LD) when linking userprogs. userprogs are linked
+with CC, so $(USERLDFLAGS) should include "-Wl," prefix as applicable.
+
+KBUILD_KCONFIG
+--------------
+Set the top-level Kconfig file to the value of this environment
+variable.  The default name is "Kconfig".
+
+KBUILD_VERBOSE
+--------------
+Set the kbuild verbosity. Can be assigned same values as "V=...".
+
+See make help for the full list.
+
+Setting "V=..." takes precedence over KBUILD_VERBOSE.
+
+KBUILD_EXTMOD
+-------------
+Set the directory to look for the kernel source when building external
+modules.
+
+Setting "M=..." takes precedence over KBUILD_EXTMOD.
+
+KBUILD_OUTPUT
+-------------
+Specify the output directory when building the kernel.
+
+This variable can also be used to point to the kernel output directory when
+building external modules against a pre-built kernel in a separate build
+directory. Please note that this does NOT specify the output directory for the
+external modules themselves. (Use KBUILD_EXTMOD_OUTPUT for that purpose.)
+
+The output directory can also be specified using "O=...".
+
+Setting "O=..." takes precedence over KBUILD_OUTPUT.
+
+KBUILD_EXTMOD_OUTPUT
+--------------------
+Specify the output directory for external modules.
+
+Setting "MO=..." takes precedence over KBUILD_EXTMOD_OUTPUT.
+
+KBUILD_EXTRA_WARN
+-----------------
+Specify the extra build checks. The same value can be assigned by passing
+W=... from the command line.
+
+See `make help` for the list of the supported values.
+
+Setting "W=..." takes precedence over KBUILD_EXTRA_WARN.
+
+KBUILD_DEBARCH
+--------------
+For the deb-pkg target, allows overriding the normal heuristics deployed by
+deb-pkg. Normally deb-pkg attempts to guess the right architecture based on
+the UTS_MACHINE variable, and on some architectures also the kernel config.
+The value of KBUILD_DEBARCH is assumed (not checked) to be a valid Debian
+architecture.
+
+KDOCFLAGS
+---------
+Specify extra (warning/error) flags for kernel-doc checks during the build,
+see tools/docs/kernel-doc for which flags are supported. Note that this doesn't
+(currently) apply to documentation builds.
+
+ARCH
+----
+Set ARCH to the architecture to be built.
+
+In most cases the name of the architecture is the same as the
+directory name found in the arch/ directory.
+
+But some architectures such as x86 and sparc have aliases.
+
+- x86: i386 for 32 bit, x86_64 for 64 bit
+- parisc: parisc64 for 64 bit
+- sparc: sparc32 for 32 bit, sparc64 for 64 bit
+
+CROSS_COMPILE
+-------------
+Specify an optional fixed part of the binutils filename.
+CROSS_COMPILE can be a part of the filename or the full path.
+
+CROSS_COMPILE is also used for ccache in some setups.
+
+CF
+--
+Additional options for sparse.
+
+CF is often used on the command-line like this::
+
+    make CF=-Wbitwise C=2
+
+INSTALL_PATH
+------------
+INSTALL_PATH specifies where to place the updated kernel and system map
+images. Default is /boot, but you can set it to other values.
+
+INSTALLKERNEL
+-------------
+Install script called when using "make install".
+The default name is "installkernel".
+
+The script will be called with the following arguments:
+
+   - $1 - kernel version
+   - $2 - kernel image file
+   - $3 - kernel map file
+   - $4 - default install path (use root directory if blank)
+
+The implementation of "make install" is architecture specific
+and it may differ from the above.
+
+INSTALLKERNEL is provided to enable the possibility to
+specify a custom installer when cross compiling a kernel.
+
+MODLIB
+------
+Specify where to install modules.
+The default value is::
+
+     $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE)
+
+The value can be overridden in which case the default value is ignored.
+
+INSTALL_MOD_PATH
+----------------
+INSTALL_MOD_PATH specifies a prefix to MODLIB for module directory
+relocations required by build roots.  This is not defined in the
+makefile but the argument can be passed to make if needed.
+
+INSTALL_MOD_STRIP
+-----------------
+INSTALL_MOD_STRIP, if defined, will cause modules to be
+stripped after they are installed.  If INSTALL_MOD_STRIP is '1', then
+the default option --strip-debug will be used.  Otherwise,
+INSTALL_MOD_STRIP value will be used as the options to the strip command.
+
+INSTALL_HDR_PATH
+----------------
+INSTALL_HDR_PATH specifies where to install user space headers when
+executing "make headers_*".
+
+The default value is::
+
+    $(objtree)/usr
+
+$(objtree) is the directory where output files are saved.
+The output directory is often set using "O=..." on the commandline.
+
+The value can be overridden in which case the default value is ignored.
+
+INSTALL_DTBS_PATH
+-----------------
+INSTALL_DTBS_PATH specifies where to install device tree blobs for
+relocations required by build roots.  This is not defined in the
+makefile but the argument can be passed to make if needed.
+
+KBUILD_ABS_SRCTREE
+--------------------------------------------------
+Kbuild uses a relative path to point to the tree when possible. For instance,
+when building in the source tree, the source tree path is '.'
+
+Setting this flag requests Kbuild to use absolute path to the source tree.
+There are some useful cases to do so, like when generating tag files with
+absolute path entries etc.
+
+KBUILD_SIGN_PIN
+---------------
+This variable allows a passphrase or PIN to be passed to the sign-file
+utility when signing kernel modules, if the private key requires such.
+
+KBUILD_MODPOST_WARN
+-------------------
+KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
+symbols in the final module linking stage. It changes such errors
+into warnings.
+
+KBUILD_MODPOST_NOFINAL
+----------------------
+KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
+This is solely useful to speed up test compiles.
+
+KBUILD_EXTRA_SYMBOLS
+--------------------
+For modules that use symbols from other modules.
+See more details in modules.rst.
+
+ALLSOURCE_ARCHS
+---------------
+For tags/TAGS/cscope targets, you can specify more than one arch
+to be included in the databases, separated by blank space. E.g.::
+
+    $ make ALLSOURCE_ARCHS="x86 mips arm" tags
+
+To get all available archs you can also specify all. E.g.::
+
+    $ make ALLSOURCE_ARCHS=all tags
+
+IGNORE_DIRS
+-----------
+For tags/TAGS/cscope targets, you can choose which directories won't
+be included in the databases, separated by blank space. E.g.::
+
+    $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope
+
+KBUILD_BUILD_TIMESTAMP
+----------------------
+Setting this to a date string overrides the timestamp used in the
+UTS_VERSION definition (uname -v in the running kernel). The value has to
+be a string that can be passed to date -d. E.g.::
+
+    $ KBUILD_BUILD_TIMESTAMP="Mon Oct 13 00:00:00 UTC 2025" make
+
+The default value is the output of the date command at one point during
+build. If provided, this timestamp will also be used for mtime fields
+within any initramfs archive. Initramfs mtimes are 32-bit, so dates before
+the 1970 Unix epoch, or after 2106-02-07 06:28:15 UTC will fail.
+
+KBUILD_BUILD_USER, KBUILD_BUILD_HOST
+------------------------------------
+These two variables allow to override the user@host string displayed during
+boot and in /proc/version. The default value is the output of the commands
+whoami and host, respectively.
+
+LLVM
+----
+If this variable is set to 1, Kbuild will use Clang and LLVM utilities instead
+of GCC and GNU binutils to build the kernel.
diff --git a/Documentation/kbuild/kconfig-language.rst b/Documentation/kbuild/kconfig-language.rst
new file mode 100644
index 000000000..d9338407c
--- /dev/null
+++ b/Documentation/kbuild/kconfig-language.rst
@@ -0,0 +1,827 @@
+================
+Kconfig Language
+================
+
+Introduction
+------------
+
+The configuration database is a collection of configuration options
+organized in a tree structure::
+
+	+- Code maturity level options
+	|  +- Prompt for development and/or incomplete code/drivers
+	+- General setup
+	|  +- Networking support
+	|  +- System V IPC
+	|  +- BSD Process Accounting
+	|  +- Sysctl support
+	+- Loadable module support
+	|  +- Enable loadable module support
+	|     +- Set version information on all module symbols
+	|     +- Kernel module loader
+	+- ...
+
+Every entry has its own dependencies. These dependencies are used
+to determine the visibility of an entry. Any child entry is only
+visible if its parent entry is also visible.
+
+Menu entries
+------------
+
+Most entries define a config option; all other entries help to organize
+them. A single configuration option is defined like this::
+
+  config MODVERSIONS
+	bool "Set version information on all module symbols"
+	depends on MODULES
+	help
+	  Usually, modules have to be recompiled whenever you switch to a new
+	  kernel.  ...
+
+Every line starts with a key word and can be followed by multiple
+arguments.  "config" starts a new config entry. The following lines
+define attributes for this config option. Attributes can be the type of
+the config option, input prompt, dependencies, help text and default
+values. A config option can be defined multiple times with the same
+name, but every definition can have only a single input prompt and the
+type must not conflict.
+
+Menu attributes
+---------------
+
+A menu entry can have a number of attributes. Not all of them are
+applicable everywhere (see syntax).
+
+- type definition: "bool"/"tristate"/"string"/"hex"/"int"
+
+  Every config option must have a type. There are only two basic types:
+  tristate and string; the other types are based on these two. The type
+  definition optionally accepts an input prompt, so these two examples
+  are equivalent::
+
+	bool "Networking support"
+
+  and::
+
+	bool
+	prompt "Networking support"
+
+- input prompt: "prompt" <prompt> ["if" <expr>]
+
+  Every menu entry can have at most one prompt, which is used to display
+  to the user. Optionally dependencies only for this prompt can be added
+  with "if". If a prompt is not present, the config option is a non-visible
+  symbol, meaning its value cannot be directly changed by the user (such as
+  altering the value in ``.config``) and the option will not appear in any
+  config menus. Its value can only be set via "default" and "select" (see
+  below).
+
+- default value: "default" <expr> ["if" <expr>]
+
+  A config option can have any number of default values. If multiple
+  default values are visible, only the first defined one is active.
+  Default values are not limited to the menu entry where they are
+  defined. This means the default can be defined somewhere else or be
+  overridden by an earlier definition.
+  The default value is only assigned to the config symbol if no other
+  value was set by the user (via the input prompt above). If an input
+  prompt is visible the default value is presented to the user and can
+  be overridden by him.
+  Optionally, dependencies only for this default value can be added with
+  "if".
+
+ The default value deliberately defaults to 'n' in order to avoid bloating the
+ build. With few exceptions, new config options should not change this. The
+ intent is for "make oldconfig" to add as little as possible to the config from
+ release to release.
+
+ Note:
+	Things that merit "default y/m" include:
+
+	a) A new Kconfig option for something that used to always be built
+	   should be "default y".
+
+	b) A new gatekeeping Kconfig option that hides/shows other Kconfig
+	   options (but does not generate any code of its own), should be
+	   "default y" so people will see those other options.
+
+	c) Sub-driver behavior or similar options for a driver that is
+	   "default n". This allows you to provide sane defaults.
+
+	d) Hardware or infrastructure that everybody expects, such as CONFIG_NET
+	   or CONFIG_BLOCK. These are rare exceptions.
+
+- type definition + default value::
+
+	"def_bool"/"def_tristate" <expr> ["if" <expr>]
+
+  This is a shorthand notation for a type definition plus a value.
+  Optionally dependencies for this default value can be added with "if".
+
+- dependencies: "depends on" <expr> ["if" <expr>]
+
+  This defines a dependency for this menu entry. If multiple
+  dependencies are defined, they are connected with '&&'. Dependencies
+  are applied to all other options within this menu entry (which also
+  accept an "if" expression), so these two examples are equivalent::
+
+	bool "foo" if BAR
+	default y if BAR
+
+  and::
+
+	depends on BAR
+	bool "foo"
+	default y
+
+  The dependency definition itself may be conditional by appending "if"
+  followed by an expression. For example::
+
+    config FOO
+	tristate
+	depends on BAR if BAZ
+
+  meaning that FOO is constrained by the value of BAR only if BAZ is
+  also set.
+
+- reverse dependencies: "select" <symbol> ["if" <expr>]
+
+  While normal dependencies reduce the upper limit of a symbol (see
+  below), reverse dependencies can be used to force a lower limit of
+  another symbol. The value of the current menu symbol is used as the
+  minimal value <symbol> can be set to. If <symbol> is selected multiple
+  times, the limit is set to the largest selection.
+  Reverse dependencies can only be used with boolean or tristate
+  symbols.
+
+  Note:
+	select should be used with care. select will force
+	a symbol to a value without visiting the dependencies.
+	By abusing select you are able to select a symbol FOO even
+	if FOO depends on BAR that is not set.
+	In general use select only for non-visible symbols
+	(no prompts anywhere) and for symbols with no dependencies.
+	That will limit the usefulness but on the other hand avoid
+	the illegal configurations all over.
+
+	If "select" <symbol> is followed by "if" <expr>, <symbol> will be
+	selected by the logical AND of the value of the current menu symbol
+	and <expr>. This means, the lower limit can be downgraded due to the
+	presence of "if" <expr>. This behavior may seem weird, but we rely on
+	it. (The future of this behavior is undecided.)
+
+- weak reverse dependencies: "imply" <symbol> ["if" <expr>]
+
+  This is similar to "select" as it enforces a lower limit on another
+  symbol except that the "implied" symbol's value may still be set to n
+  from a direct dependency or with a visible prompt.
+
+  Given the following example::
+
+    config FOO
+	tristate "foo"
+	imply BAZ
+
+    config BAZ
+	tristate "baz"
+	depends on BAR
+
+  The following values are possible:
+
+	===		===		=============	==============
+	FOO		BAR		BAZ's default	choice for BAZ
+	===		===		=============	==============
+	n		y		n		N/m/y
+	m		y		m		M/y/n
+	y		y		y		Y/m/n
+	n		m		n		N/m
+	m		m		m		M/n
+	y		m		m		M/n
+	y		n		*		N
+	===		===		=============	==============
+
+  This is useful e.g. with multiple drivers that want to indicate their
+  ability to hook into a secondary subsystem while allowing the user to
+  configure that subsystem out without also having to unset these drivers.
+
+  Note: If the feature provided by BAZ is highly desirable for FOO,
+  FOO should imply not only BAZ, but also its dependency BAR::
+
+    config FOO
+	tristate "foo"
+	imply BAR
+	imply BAZ
+
+  Note: If "imply" <symbol> is followed by "if" <expr>, the default of <symbol>
+  will be the logical AND of the value of the current menu symbol and <expr>.
+  (The future of this behavior is undecided.)
+
+- limiting menu display: "visible if" <expr>
+
+  This attribute is only applicable to menu blocks, if the condition is
+  false, the menu block is not displayed to the user (the symbols
+  contained there can still be selected by other symbols, though). It is
+  similar to a conditional "prompt" attribute for individual menu
+  entries. Default value of "visible" is true.
+
+- numerical ranges: "range" <symbol> <symbol> ["if" <expr>]
+
+  This allows limiting the range of possible input values for int
+  and hex symbols. The user can only input a value which is larger than
+  or equal to the first symbol and smaller than or equal to the second
+  symbol.
+
+- help text: "help"
+
+  This defines a help text. The end of the help text is determined by
+  the indentation level, this means it ends at the first line which has
+  a smaller indentation than the first line of the help text.
+
+- module attribute: "modules"
+  This declares the symbol to be used as the MODULES symbol, which
+  enables the third modular state for all config symbols.
+  At most one symbol may have the "modules" option set.
+
+- transitional attribute: "transitional"
+  This declares the symbol as transitional, meaning it should be processed
+  during configuration but omitted from newly written .config files.
+  Transitional symbols are useful for backward compatibility during config
+  option migrations - they allow olddefconfig to process existing .config
+  files while ensuring the old option doesn't appear in new configurations.
+
+  A transitional symbol:
+  - Has no prompt (is not visible to users in menus)
+  - Is processed normally during configuration (values are read and used)
+  - Can be referenced in default expressions of other symbols
+  - Is not written to new .config files
+  - Cannot have any other properties (it is a pass-through option)
+
+  Example migration from OLD_NAME to NEW_NAME::
+
+    config NEW_NAME
+	bool "New option name"
+	default OLD_NAME
+	help
+	  This replaces the old CONFIG_OLD_NAME option.
+
+    config OLD_NAME
+	bool
+	transitional
+	help
+	  Transitional config for OLD_NAME to NEW_NAME migration.
+
+  With this setup, existing .config files with "CONFIG_OLD_NAME=y" will
+  result in "CONFIG_NEW_NAME=y" being set, while CONFIG_OLD_NAME will be
+  omitted from newly written .config files.
+
+Menu dependencies
+-----------------
+
+Dependencies define the visibility of a menu entry and can also reduce
+the input range of tristate symbols. The tristate logic used in the
+expressions uses one more state than normal boolean logic to express the
+module state. Dependency expressions have the following syntax::
+
+  <expr> ::= <symbol>                           (1)
+           <symbol> '=' <symbol>                (2)
+           <symbol> '!=' <symbol>               (3)
+           <symbol1> '<' <symbol2>              (4)
+           <symbol1> '>' <symbol2>              (4)
+           <symbol1> '<=' <symbol2>             (4)
+           <symbol1> '>=' <symbol2>             (4)
+           '(' <expr> ')'                       (5)
+           '!' <expr>                           (6)
+           <expr> '&&' <expr>                   (7)
+           <expr> '||' <expr>                   (8)
+
+Expressions are listed in decreasing order of precedence.
+
+(1) Convert the symbol into an expression. Boolean and tristate symbols
+    are simply converted into the respective expression values. All
+    other symbol types result in 'n'.
+(2) If the values of both symbols are equal, it returns 'y',
+    otherwise 'n'.
+(3) If the values of both symbols are equal, it returns 'n',
+    otherwise 'y'.
+(4) If value of <symbol1> is respectively lower, greater, lower-or-equal,
+    or greater-or-equal than value of <symbol2>, it returns 'y',
+    otherwise 'n'.
+(5) Returns the value of the expression. Used to override precedence.
+(6) Returns the result of (2-/expr/).
+(7) Returns the result of min(/expr/, /expr/).
+(8) Returns the result of max(/expr/, /expr/).
+
+An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
+respectively for calculations). A menu entry becomes visible when its
+expression evaluates to 'm' or 'y'.
+
+There are two types of symbols: constant and non-constant symbols.
+Non-constant symbols are the most common ones and are defined with the
+'config' statement. Non-constant symbols consist entirely of alphanumeric
+characters or underscores.
+Constant symbols are only part of expressions. Constant symbols are
+always surrounded by single or double quotes. Within the quote, any
+other character is allowed and the quotes can be escaped using '\'.
+
+Menu structure
+--------------
+
+The position of a menu entry in the tree is determined in two ways. First
+it can be specified explicitly::
+
+  menu "Network device support"
+	depends on NET
+
+  config NETDEVICES
+	...
+
+  endmenu
+
+All entries within the "menu" ... "endmenu" block become a submenu of
+"Network device support". All subentries inherit the dependencies from
+the menu entry, e.g. this means the dependency "NET" is added to the
+dependency list of the config option NETDEVICES.
+
+The other way to generate the menu structure is done by analyzing the
+dependencies. If a menu entry somehow depends on the previous entry, it
+can be made a submenu of it. First, the previous (parent) symbol must
+be part of the dependency list and then one of these two conditions
+must be true:
+
+- the child entry must become invisible, if the parent is set to 'n'
+- the child entry must only be visible, if the parent is visible::
+
+    config MODULES
+	bool "Enable loadable module support"
+
+    config MODVERSIONS
+	bool "Set version information on all module symbols"
+	depends on MODULES
+
+    comment "module support disabled"
+	depends on !MODULES
+
+MODVERSIONS directly depends on MODULES, this means it's only visible if
+MODULES is different from 'n'. The comment on the other hand is only
+visible when MODULES is set to 'n'.
+
+
+Kconfig syntax
+--------------
+
+The configuration file describes a series of menu entries, where every
+line starts with a keyword (except help texts). The following keywords
+end a menu entry:
+
+- config
+- menuconfig
+- choice/endchoice
+- comment
+- menu/endmenu
+- if/endif
+- source
+
+The first five also start the definition of a menu entry.
+
+config::
+
+	"config" <symbol>
+	<config options>
+
+This defines a config symbol <symbol> and accepts any of above
+attributes as options.
+
+menuconfig::
+
+	"menuconfig" <symbol>
+	<config options>
+
+This is similar to the simple config entry above, but it also gives a
+hint to front ends, that all suboptions should be displayed as a
+separate list of options. To make sure all the suboptions will really
+show up under the menuconfig entry and not outside of it, every item
+from the <config options> list must depend on the menuconfig symbol.
+In practice, this is achieved by using one of the next two constructs::
+
+  (1):
+  menuconfig M
+  if M
+      config C1
+      config C2
+  endif
+
+  (2):
+  menuconfig M
+  config C1
+      depends on M
+  config C2
+      depends on M
+
+In the following examples (3) and (4), C1 and C2 still have the M
+dependency, but will not appear under menuconfig M anymore, because
+of C0, which doesn't depend on M::
+
+  (3):
+  menuconfig M
+      config C0
+  if M
+      config C1
+      config C2
+  endif
+
+  (4):
+  menuconfig M
+  config C0
+  config C1
+      depends on M
+  config C2
+      depends on M
+
+choices::
+
+	"choice"
+	<choice options>
+	<choice block>
+	"endchoice"
+
+This defines a choice group and accepts "prompt", "default", "depends on", and
+"help" attributes as options.
+
+A choice only allows a single config entry to be selected.
+
+comment::
+
+	"comment" <prompt>
+	<comment options>
+
+This defines a comment which is displayed to the user during the
+configuration process and is also echoed to the output files. The only
+possible options are dependencies.
+
+menu::
+
+	"menu" <prompt>
+	<menu options>
+	<menu block>
+	"endmenu"
+
+This defines a menu block, see "Menu structure" above for more
+information. The only possible options are dependencies and "visible"
+attributes.
+
+if::
+
+	"if" <expr>
+	<if block>
+	"endif"
+
+This defines an if block. The dependency expression <expr> is appended
+to all enclosed menu entries.
+
+source::
+
+	"source" <prompt>
+
+This reads the specified configuration file. This file is always parsed.
+
+mainmenu::
+
+	"mainmenu" <prompt>
+
+This sets the config program's title bar if the config program chooses
+to use it. It should be placed at the top of the configuration, before any
+other statement.
+
+'#' Kconfig source file comment:
+
+An unquoted '#' character anywhere in a source file line indicates
+the beginning of a source file comment.  The remainder of that line
+is a comment.
+
+
+Kconfig hints
+-------------
+This is a collection of Kconfig tips, most of which aren't obvious at
+first glance and most of which have become idioms in several Kconfig
+files.
+
+Adding common features and make the usage configurable
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is a common idiom to implement a feature/functionality that are
+relevant for some architectures but not all.
+The recommended way to do so is to use a config variable named HAVE_*
+that is defined in a common Kconfig file and selected by the relevant
+architectures.
+An example is the generic IOMAP functionality.
+
+We would in lib/Kconfig see::
+
+  # Generic IOMAP is used to ...
+  config HAVE_GENERIC_IOMAP
+
+  config GENERIC_IOMAP
+	depends on HAVE_GENERIC_IOMAP && FOO
+
+And in lib/Makefile we would see::
+
+	obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
+
+For each architecture using the generic IOMAP functionality we would see::
+
+  config X86
+	select ...
+	select HAVE_GENERIC_IOMAP
+	select ...
+
+Note: we use the existing config option and avoid creating a new
+config variable to select HAVE_GENERIC_IOMAP.
+
+Note: the use of the internal config variable HAVE_GENERIC_IOMAP, it is
+introduced to overcome the limitation of select which will force a
+config option to 'y' no matter the dependencies.
+The dependencies are moved to the symbol GENERIC_IOMAP and we avoid the
+situation where select forces a symbol equals to 'y'.
+
+Adding features that need compiler support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+There are several features that need compiler support. The recommended way
+to describe the dependency on the compiler feature is to use "depends on"
+followed by a test macro::
+
+  config STACKPROTECTOR
+	bool "Stack Protector buffer overflow detection"
+	depends on $(cc-option,-fstack-protector)
+	...
+
+If you need to expose a compiler capability to makefiles and/or C source files,
+`CC_HAS_` is the recommended prefix for the config option::
+
+  config CC_HAS_FOO
+	def_bool $(success,$(srctree)/scripts/cc-check-foo.sh $(CC))
+
+Build as module only
+~~~~~~~~~~~~~~~~~~~~
+To restrict a component build to module-only, qualify its config symbol
+with "depends on m".  E.g.::
+
+  config FOO
+	depends on BAR && m
+
+limits FOO to module (=m) or disabled (=n).
+
+Compile-testing
+~~~~~~~~~~~~~~~
+If a config symbol has a dependency, but the code controlled by the config
+symbol can still be compiled if the dependency is not met, it is encouraged to
+increase build coverage by adding an "|| COMPILE_TEST" clause to the
+dependency. This is especially useful for drivers for more exotic hardware, as
+it allows continuous-integration systems to compile-test the code on a more
+common system, and detect bugs that way.
+Note that compile-tested code should avoid crashing when run on a system where
+the dependency is not met.
+
+Architecture and platform dependencies
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Due to the presence of stubs, most drivers can now be compiled on most
+architectures. However, this does not mean it makes sense to have all drivers
+available everywhere, as the actual hardware may only exist on specific
+architectures and platforms. This is especially true for on-SoC IP cores,
+which may be limited to a specific vendor or SoC family.
+
+To prevent asking the user about drivers that cannot be used on the system(s)
+the user is compiling a kernel for, and if it makes sense, config symbols
+controlling the compilation of a driver should contain proper dependencies,
+limiting the visibility of the symbol to (a superset of) the platform(s) the
+driver can be used on. The dependency can be an architecture (e.g. ARM) or
+platform (e.g. ARCH_OMAP4) dependency. This makes life simpler not only for
+distro config owners, but also for every single developer or user who
+configures a kernel.
+
+Such a dependency can be relaxed by combining it with the compile-testing rule
+above, leading to:
+
+  config FOO
+	bool "Support for foo hardware"
+	depends on ARCH_FOO_VENDOR || COMPILE_TEST
+
+Optional dependencies
+~~~~~~~~~~~~~~~~~~~~~
+
+Some drivers are able to optionally use a feature from another module
+or build cleanly with that module disabled, but cause a link failure
+when trying to use that loadable module from a built-in driver.
+
+The recommended way to express this optional dependency in Kconfig logic
+uses the conditional form::
+
+  config FOO
+	tristate "Support for foo hardware"
+	depends on BAR if BAR
+
+This slightly counterintuitive style is also widely used::
+
+  config FOO
+	tristate "Support for foo hardware"
+	depends on BAR || !BAR
+
+This means that there is either a dependency on BAR that disallows
+the combination of FOO=y with BAR=m, or BAR is completely disabled. The BAR
+module must provide all the stubs for !BAR case.
+
+For a more formalized approach if there are multiple drivers that have
+the same dependency, a helper symbol can be used, like::
+
+  config FOO
+	tristate "Support for foo hardware"
+	depends on BAR_OPTIONAL
+
+  config BAR_OPTIONAL
+	def_tristate BAR || !BAR
+
+Much less favorable way to express optional dependency is IS_REACHABLE() within
+the module code, useful for example when the module BAR does not provide
+!BAR stubs::
+
+	foo_init()
+	{
+		if (IS_REACHABLE(CONFIG_BAR))
+			bar_register(&foo);
+		...
+	}
+
+IS_REACHABLE() is generally discouraged, because the code will be silently
+discarded, when CONFIG_BAR=m and this code is built-in. This is not what users
+usually expect when enabling BAR as module.
+
+Kconfig recursive dependency limitations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you've hit the Kconfig error: "recursive dependency detected" you've run
+into a recursive dependency issue with Kconfig, a recursive dependency can be
+summarized as a circular dependency. The kconfig tools need to ensure that
+Kconfig files comply with specified configuration requirements. In order to do
+that kconfig must determine the values that are possible for all Kconfig
+symbols, this is currently not possible if there is a circular relation
+between two or more Kconfig symbols. For more details refer to the "Simple
+Kconfig recursive issue" subsection below. Kconfig does not do recursive
+dependency resolution; this has a few implications for Kconfig file writers.
+We'll first explain why this issues exists and then provide an example
+technical limitation which this brings upon Kconfig developers. Eager
+developers wishing to try to address this limitation should read the next
+subsections.
+
+Simple Kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Read: Documentation/kbuild/Kconfig.recursion-issue-01
+
+Test with::
+
+  make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-01 allnoconfig
+
+Cumulative Kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Read: Documentation/kbuild/Kconfig.recursion-issue-02
+
+Test with::
+
+  make KBUILD_KCONFIG=Documentation/kbuild/Kconfig.recursion-issue-02 allnoconfig
+
+Practical solutions to kconfig recursive issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Developers who run into the recursive Kconfig issue have two options
+at their disposal. We document them below and also provide a list of
+historical issues resolved through these different solutions.
+
+  a) Remove any superfluous "select FOO" or "depends on FOO"
+  b) Match dependency semantics:
+
+	b1) Swap all "select FOO" to "depends on FOO" or,
+
+	b2) Swap all "depends on FOO" to "select FOO"
+
+The resolution to a) can be tested with the sample Kconfig file
+Documentation/kbuild/Kconfig.recursion-issue-01 through the removal
+of the "select CORE" from CORE_BELL_A_ADVANCED as that is implicit already
+since CORE_BELL_A depends on CORE. At times it may not be possible to remove
+some dependency criteria, for such cases you can work with solution b).
+
+The two different resolutions for b) can be tested in the sample Kconfig file
+Documentation/kbuild/Kconfig.recursion-issue-02.
+
+Below is a list of examples of prior fixes for these types of recursive issues;
+all errors appear to involve one or more "select" statements and one or more
+"depends on".
+
+============    ===================================
+commit          fix
+============    ===================================
+06b718c01208    select A -> depends on A
+c22eacfe82f9    depends on A -> depends on B
+6a91e854442c    select A -> depends on A
+118c565a8f2e    select A -> select B
+f004e5594705    select A -> depends on A
+c7861f37b4c6    depends on A -> (null)
+80c69915e5fb    select A -> (null)              (1)
+c2218e26c0d0    select A -> depends on A        (1)
+d6ae99d04e1c    select A -> depends on A
+95ca19cf8cbf    select A -> depends on A
+8f057d7bca54    depends on A -> (null)
+8f057d7bca54    depends on A -> select A
+a0701f04846e    select A -> depends on A
+0c8b92f7f259    depends on A -> (null)
+e4e9e0540928    select A -> depends on A        (2)
+7453ea886e87    depends on A > (null)           (1)
+7b1fff7e4fdf    select A -> depends on A
+86c747d2a4f0    select A -> depends on A
+d9f9ab51e55e    select A -> depends on A
+0c51a4d8abd6    depends on A -> select A        (3)
+e98062ed6dc4    select A -> depends on A        (3)
+91e5d284a7f1    select A -> (null)
+============    ===================================
+
+(1) Partial (or no) quote of error.
+(2) That seems to be the gist of that fix.
+(3) Same error.
+
+Future kconfig work
+~~~~~~~~~~~~~~~~~~~
+
+Work on kconfig is welcomed on both areas of clarifying semantics and on
+evaluating the use of a full SAT solver for it. A full SAT solver can be
+desirable to enable more complex dependency mappings and / or queries,
+for instance one possible use case for a SAT solver could be that of handling
+the current known recursive dependency issues. It is not known if this would
+address such issues but such evaluation is desirable. If support for a full SAT
+solver proves too complex or that it cannot address recursive dependency issues
+Kconfig should have at least clear and well defined semantics which also
+addresses and documents limitations or requirements such as the ones dealing
+with recursive dependencies.
+
+Further work on both of these areas is welcomed on Kconfig. We elaborate
+on both of these in the next two subsections.
+
+Semantics of Kconfig
+~~~~~~~~~~~~~~~~~~~~
+
+The use of Kconfig is broad, Linux is now only one of Kconfig's users:
+one study has completed a broad analysis of Kconfig use in 12 projects [0]_.
+Despite its widespread use, and although this document does a reasonable job
+in documenting basic Kconfig syntax a more precise definition of Kconfig
+semantics is welcomed. One project deduced Kconfig semantics through
+the use of the xconfig configurator [1]_. Work should be done to confirm if
+the deduced semantics matches our intended Kconfig design goals.
+Another project formalized a denotational semantics of a core subset of
+the Kconfig language [10]_.
+
+Having well defined semantics can be useful for tools for practical
+evaluation of dependencies, for instance one such case was work to
+express in boolean abstraction of the inferred semantics of Kconfig to
+translate Kconfig logic into boolean formulas and run a SAT solver on this to
+find dead code / features (always inactive), 114 dead features were found in
+Linux using this methodology [1]_ (Section 8: Threats to validity).
+The kismet tool, based on the semantics in [10]_, finds abuses of reverse
+dependencies and has led to dozens of committed fixes to Linux Kconfig files [11]_.
+
+Confirming this could prove useful as Kconfig stands as one of the leading
+industrial variability modeling languages [1]_ [2]_. Its study would help
+evaluate practical uses of such languages, their use was only theoretical
+and real world requirements were not well understood. As it stands though
+only reverse engineering techniques have been used to deduce semantics from
+variability modeling languages such as Kconfig [3]_.
+
+.. [0] https://www.eng.uwaterloo.ca/~shshe/kconfig_semantics.pdf
+.. [1] https://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+.. [2] https://gsd.uwaterloo.ca/sites/default/files/ase241-berger_0.pdf
+.. [3] https://gsd.uwaterloo.ca/sites/default/files/icse2011.pdf
+
+Full SAT solver for Kconfig
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Although SAT solvers [4]_ haven't yet been used by Kconfig directly, as noted
+in the previous subsection, work has been done however to express in boolean
+abstraction the inferred semantics of Kconfig to translate Kconfig logic into
+boolean formulas and run a SAT solver on it [5]_. Another known related project
+is CADOS [6]_ (former VAMOS [7]_) and the tools, mainly undertaker [8]_, which
+has been introduced first with [9]_.  The basic concept of undertaker is to
+extract variability models from Kconfig and put them together with a
+propositional formula extracted from CPP #ifdefs and build-rules into a SAT
+solver in order to find dead code, dead files, and dead symbols. If using a SAT
+solver is desirable on Kconfig one approach would be to evaluate repurposing
+such efforts somehow on Kconfig. There is enough interest from mentors of
+existing projects to not only help advise how to integrate this work upstream
+but also help maintain it long term. Interested developers should visit:
+
+https://kernelnewbies.org/KernelProjects/kconfig-sat
+
+.. [4] https://www.cs.cornell.edu/~sabhar/chapters/SATSolvers-KR-Handbook.pdf
+.. [5] https://gsd.uwaterloo.ca/sites/default/files/vm-2013-berger.pdf
+.. [6] https://cados.cs.fau.de
+.. [7] https://vamos.cs.fau.de
+.. [8] https://undertaker.cs.fau.de
+.. [9] https://www4.cs.fau.de/Publications/2011/tartler_11_eurosys.pdf
+.. [10] https://paulgazzillo.com/papers/esecfse21.pdf
+.. [11] https://github.com/paulgazz/kmax
diff --git a/Documentation/kbuild/kconfig-macro-language.rst b/Documentation/kbuild/kconfig-macro-language.rst
new file mode 100644
index 000000000..6163467f6
--- /dev/null
+++ b/Documentation/kbuild/kconfig-macro-language.rst
@@ -0,0 +1,247 @@
+======================
+Kconfig macro language
+======================
+
+Concept
+-------
+
+The basic idea was inspired by Make. When we look at Make, we notice sort of
+two languages in one. One language describes dependency graphs consisting of
+targets and prerequisites. The other is a macro language for performing textual
+substitution.
+
+There is clear distinction between the two language stages. For example, you
+can write a makefile like follows::
+
+    APP := foo
+    SRC := foo.c
+    CC := gcc
+
+    $(APP): $(SRC)
+            $(CC) -o $(APP) $(SRC)
+
+The macro language replaces the variable references with their expanded form,
+and handles as if the source file were input like follows::
+
+    foo: foo.c
+            gcc -o foo foo.c
+
+Then, Make analyzes the dependency graph and determines the targets to be
+updated.
+
+The idea is quite similar in Kconfig - it is possible to describe a Kconfig
+file like this::
+
+    CC := gcc
+
+    config CC_HAS_FOO
+            def_bool $(shell, $(srctree)/scripts/gcc-check-foo.sh $(CC))
+
+The macro language in Kconfig processes the source file into the following
+intermediate::
+
+    config CC_HAS_FOO
+            def_bool y
+
+Then, Kconfig moves onto the evaluation stage to resolve inter-symbol
+dependency as explained in kconfig-language.rst.
+
+
+Variables
+---------
+
+Like in Make, a variable in Kconfig works as a macro variable.  A macro
+variable is expanded "in place" to yield a text string that may then be
+expanded further. To get the value of a variable, enclose the variable name in
+$( ). The parentheses are required even for single-letter variable names; $X is
+a syntax error. The curly brace form as in ${CC} is not supported either.
+
+There are two types of variables: simply expanded variables and recursively
+expanded variables.
+
+A simply expanded variable is defined using the := assignment operator. Its
+righthand side is expanded immediately upon reading the line from the Kconfig
+file.
+
+A recursively expanded variable is defined using the = assignment operator.
+Its righthand side is simply stored as the value of the variable without
+expanding it in any way. Instead, the expansion is performed when the variable
+is used.
+
+There is another type of assignment operator; += is used to append text to a
+variable. The righthand side of += is expanded immediately if the lefthand
+side was originally defined as a simple variable. Otherwise, its evaluation is
+deferred.
+
+The variable reference can take parameters, in the following form::
+
+  $(name,arg1,arg2,arg3)
+
+You can consider the parameterized reference as a function. (more precisely,
+"user-defined function" in contrast to "built-in function" listed below).
+
+Useful functions must be expanded when they are used since the same function is
+expanded differently if different parameters are passed. Hence, a user-defined
+function is defined using the = assignment operator. The parameters are
+referenced within the body definition with $(1), $(2), etc.
+
+In fact, recursively expanded variables and user-defined functions are the same
+internally. (In other words, "variable" is "function with zero argument".)
+When we say "variable" in a broad sense, it includes "user-defined function".
+
+
+Built-in functions
+------------------
+
+Like Make, Kconfig provides several built-in functions. Every function takes a
+particular number of arguments.
+
+In Make, every built-in function takes at least one argument. Kconfig allows
+zero argument for built-in functions, such as $(filename), $(lineno). You could
+consider those as "built-in variable", but it is just a matter of how we call
+it after all. Let's say "built-in function" here to refer to natively supported
+functionality.
+
+Kconfig currently supports the following built-in functions.
+
+ - $(shell,command)
+
+  The "shell" function accepts a single argument that is expanded and passed
+  to a subshell for execution. The standard output of the command is then read
+  and returned as the value of the function. Every newline in the output is
+  replaced with a space. Any trailing newlines are deleted. The standard error
+  is not returned, nor is any program exit status.
+
+ - $(info,text)
+
+  The "info" function takes a single argument and prints it to stdout.
+  It evaluates to an empty string.
+
+ - $(warning-if,condition,text)
+
+  The "warning-if" function takes two arguments. If the condition part is "y",
+  the text part is sent to stderr. The text is prefixed with the name of the
+  current Kconfig file and the current line number.
+
+ - $(error-if,condition,text)
+
+  The "error-if" function is similar to "warning-if", but it terminates the
+  parsing immediately if the condition part is "y".
+
+ - $(filename)
+
+  The 'filename' takes no argument, and $(filename) is expanded to the file
+  name being parsed.
+
+ - $(lineno)
+
+  The 'lineno' takes no argument, and $(lineno) is expanded to the line number
+  being parsed.
+
+
+Make vs Kconfig
+---------------
+
+Kconfig adopts Make-like macro language, but the function call syntax is
+slightly different.
+
+A function call in Make looks like this::
+
+  $(func-name arg1,arg2,arg3)
+
+The function name and the first argument are separated by at least one
+whitespace. Then, leading whitespaces are trimmed from the first argument,
+while whitespaces in the other arguments are kept. You need to use a kind of
+trick to start the first parameter with spaces. For example, if you want
+to make "info" function print "  hello", you can write like follows::
+
+  empty :=
+  space := $(empty) $(empty)
+  $(info $(space)$(space)hello)
+
+Kconfig uses only commas for delimiters, and keeps all whitespaces in the
+function call. Some people prefer putting a space after each comma delimiter::
+
+  $(func-name, arg1, arg2, arg3)
+
+In this case, "func-name" will receive " arg1", " arg2", " arg3". The presence
+of leading spaces may matter depending on the function. The same applies to
+Make - for example, $(subst .c, .o, $(sources)) is a typical mistake; it
+replaces ".c" with " .o".
+
+In Make, a user-defined function is referenced by using a built-in function,
+'call', like this::
+
+    $(call my-func,arg1,arg2,arg3)
+
+Kconfig invokes user-defined functions and built-in functions in the same way.
+The omission of 'call' makes the syntax shorter.
+
+In Make, some functions treat commas verbatim instead of argument separators.
+For example, $(shell echo hello, world) runs the command "echo hello, world".
+Likewise, $(info hello, world) prints "hello, world" to stdout. You could say
+this is _useful_ inconsistency.
+
+In Kconfig, for simpler implementation and grammatical consistency, commas that
+appear in the $( ) context are always delimiters. It means::
+
+  $(shell, echo hello, world)
+
+is an error because it is passing two parameters where the 'shell' function
+accepts only one. To pass commas in arguments, you can use the following trick::
+
+  comma := ,
+  $(shell, echo hello$(comma) world)
+
+
+Caveats
+-------
+
+A variable (or function) cannot be expanded across tokens. So, you cannot use
+a variable as a shorthand for an expression that consists of multiple tokens.
+The following works::
+
+    RANGE_MIN := 1
+    RANGE_MAX := 3
+
+    config FOO
+            int "foo"
+            range $(RANGE_MIN) $(RANGE_MAX)
+
+But, the following does not work::
+
+    RANGES := 1 3
+
+    config FOO
+            int "foo"
+            range $(RANGES)
+
+A variable cannot be expanded to any keyword in Kconfig.  The following does
+not work::
+
+    MY_TYPE := tristate
+
+    config FOO
+            $(MY_TYPE) "foo"
+            default y
+
+Obviously from the design, $(shell command) is expanded in the textual
+substitution phase. You cannot pass symbols to the 'shell' function.
+
+The following does not work as expected::
+
+    config ENDIAN_FLAG
+            string
+            default "-mbig-endian" if CPU_BIG_ENDIAN
+            default "-mlittle-endian" if CPU_LITTLE_ENDIAN
+
+    config CC_HAS_ENDIAN_FLAG
+            def_bool $(shell $(srctree)/scripts/gcc-check-flag ENDIAN_FLAG)
+
+Instead, you can do like follows so that any function call is statically
+expanded::
+
+    config CC_HAS_ENDIAN_FLAG
+            bool
+            default $(shell $(srctree)/scripts/gcc-check-flag -mbig-endian) if CPU_BIG_ENDIAN
+            default $(shell $(srctree)/scripts/gcc-check-flag -mlittle-endian) if CPU_LITTLE_ENDIAN
diff --git a/Documentation/kbuild/kconfig.rst b/Documentation/kbuild/kconfig.rst
new file mode 100644
index 000000000..e35dd1d5f
--- /dev/null
+++ b/Documentation/kbuild/kconfig.rst
@@ -0,0 +1,300 @@
+=================================
+Configuration targets and editors
+=================================
+
+This file contains some assistance for using ``make *config``.
+
+Use ``make help`` to list all of the possible configuration targets.
+
+The xconfig ('qconf'), menuconfig ('mconf'), and nconfig ('nconf')
+programs also have embedded help text.  Be sure to check that for
+navigation, search, and other general help text.
+
+The gconfig ('gconf') program has limited help text.
+
+
+General
+=======
+
+New kernel releases often introduce new config symbols.  Often more
+important, new kernel releases may rename config symbols.  When
+this happens, using a previously working .config file and running
+"make oldconfig" won't necessarily produce a working new kernel
+for you, so you may find that you need to see what NEW kernel
+symbols have been introduced.
+
+To see a list of new config symbols, use::
+
+    cp user/some/old.config .config
+    make listnewconfig
+
+and the config program will list any new symbols, one per line.
+
+Alternatively, you can use the brute force method::
+
+    make oldconfig
+    scripts/diffconfig .config.old .config | less
+
+
+Environment variables
+=====================
+
+Environment variables for ``*config``:
+
+``KCONFIG_CONFIG``
+    This environment variable can be used to specify a default kernel config
+    file name to override the default name of ".config".
+
+``KCONFIG_DEFCONFIG_LIST``
+    This environment variable specifies a list of config files which can be
+    used as a base configuration in case the .config does not exist yet.
+    Entries in the list are separated with whitespaces to each other, and
+    the first one that exists is used.
+
+``KCONFIG_OVERWRITECONFIG``
+    If you set KCONFIG_OVERWRITECONFIG in the environment, Kconfig will not
+    break symlinks when .config is a symlink to somewhere else.
+
+``KCONFIG_WARN_UNKNOWN_SYMBOLS``
+    This environment variable makes Kconfig warn about all unrecognized
+    symbols in the config input.
+
+``KCONFIG_WARN_CHANGED_INPUT``
+    If set to a non-blank value, Kconfig prints optional warnings for
+    user-provided values that change after Kconfig resolves dependencies
+    or applies other constraints such as ranges.
+
+``KCONFIG_WERROR``
+    If set, Kconfig treats warnings as errors.
+
+``CONFIG_``
+    If you set ``CONFIG_`` in the environment, Kconfig will prefix all symbols
+    with its value when saving the configuration, instead of using the
+    default, ``CONFIG_``.
+
+Environment variables for ``{allyes/allmod/allno/alldef/rand}config``:
+
+``KCONFIG_ALLCONFIG``
+    The allyesconfig/allmodconfig/alldefconfig/allnoconfig/randconfig variants
+    can also use the environment variable KCONFIG_ALLCONFIG as a flag or a
+    filename that contains config symbols that the user requires to be set to a
+    specific value.  If KCONFIG_ALLCONFIG is used without a filename where
+    KCONFIG_ALLCONFIG == "" or KCONFIG_ALLCONFIG == "1", ``make *config``
+    checks for a file named "all{yes/mod/no/def/random}.config"
+    (corresponding to the ``*config`` command that was used) for symbol values
+    that are to be forced.  If this file is not found, it checks for a
+    file named "all.config" to contain forced values.
+
+    This enables you to create "miniature" config (miniconfig) or custom
+    config files containing just the config symbols that you are interested
+    in.  Then the kernel config system generates the full .config file,
+    including symbols of your miniconfig file.
+
+    This ``KCONFIG_ALLCONFIG`` file is a config file which contains
+    (usually a subset of all) preset config symbols.  These variable
+    settings are still subject to normal dependency checks.
+
+    Examples::
+
+        KCONFIG_ALLCONFIG=custom-notebook.config make allnoconfig
+
+    or::
+
+        KCONFIG_ALLCONFIG=mini.config make allnoconfig
+
+    or::
+
+        make KCONFIG_ALLCONFIG=mini.config allnoconfig
+
+    These examples will disable most options (allnoconfig) but enable or
+    disable the options that are explicitly listed in the specified
+    mini-config files.
+
+Environment variables for ``randconfig``:
+
+``KCONFIG_SEED``
+    You can set this to the integer value used to seed the RNG, if you want
+    to somehow debug the behaviour of the kconfig parser/frontends.
+    If not set, the current time will be used.
+
+``KCONFIG_PROBABILITY``
+    This variable can be used to skew the probabilities. This variable can
+    be unset or empty, or set to three different formats:
+
+    =======================     ==================  =====================
+    KCONFIG_PROBABILITY         y:n split           y:m:n split
+    =======================     ==================  =====================
+    unset or empty              50  : 50            33  : 33  : 34
+    N                            N  : 100-N         N/2 : N/2 : 100-N
+    [1] N:M                     N+M : 100-(N+M)      N  :  M  : 100-(N+M)
+    [2] N:M:L                    N  : 100-N          M  :  L  : 100-(M+L)
+    =======================     ==================  =====================
+
+where N, M and L are integers (in base 10) in the range [0,100], and so
+that:
+
+    [1] N+M is in the range [0,100]
+
+    [2] M+L is in the range [0,100]
+
+Examples::
+
+    KCONFIG_PROBABILITY=10
+        10% of booleans will be set to 'y', 90% to 'n'
+        5% of tristates will be set to 'y', 5% to 'm', 90% to 'n'
+    KCONFIG_PROBABILITY=15:25
+        40% of booleans will be set to 'y', 60% to 'n'
+        15% of tristates will be set to 'y', 25% to 'm', 60% to 'n'
+    KCONFIG_PROBABILITY=10:15:15
+        10% of booleans will be set to 'y', 90% to 'n'
+        15% of tristates will be set to 'y', 15% to 'm', 70% to 'n'
+
+Environment variables for ``syncconfig``:
+
+``KCONFIG_NOSILENTUPDATE``
+    If this variable has a non-blank value, it prevents silent kernel
+    config updates (requires explicit updates).
+
+``KCONFIG_AUTOCONFIG``
+    This environment variable can be set to specify the path & name of the
+    "auto.conf" file.  Its default value is "include/config/auto.conf".
+
+``KCONFIG_AUTOHEADER``
+    This environment variable can be set to specify the path & name of the
+    "autoconf.h" (header) file.
+    Its default value is "include/generated/autoconf.h".
+
+
+menuconfig
+==========
+
+Searching in menuconfig:
+
+    The Search function searches for kernel configuration symbol
+    names, so you have to know something close to what you are
+    looking for.
+
+    Example::
+
+        /hotplug
+        This lists all config symbols that contain "hotplug",
+        e.g., HOTPLUG_CPU, MEMORY_HOTPLUG.
+
+    For search help, enter / followed by TAB-TAB (to highlight
+    <Help>) and Enter.  This will tell you that you can also use
+    regular expressions (regexes) in the search string, so if you
+    are not interested in MEMORY_HOTPLUG, you could try::
+
+        /^hotplug
+
+    When searching, symbols are sorted thus:
+
+    - first, exact matches, sorted alphabetically (an exact match
+      is when the search matches the complete symbol name);
+    - then, other matches, sorted alphabetically.
+
+    For example, ^ATH.K matches:
+
+        ATH5K ATH9K ATH5K_AHB ATH5K_DEBUG [...] ATH6KL ATH6KL_DEBUG
+        [...] ATH9K_AHB ATH9K_BTCOEX_SUPPORT ATH9K_COMMON [...]
+
+    of which only ATH5K and ATH9K match exactly and so are sorted
+    first (and in alphabetical order), then come all other symbols,
+    sorted in alphabetical order.
+
+    In this menu, pressing the key in the (#) prefix will jump
+    directly to that location. You will be returned to the current
+    search results after exiting this new menu.
+
+User interface options for 'menuconfig':
+
+``MENUCONFIG_COLOR``
+    It is possible to select different color themes using the variable
+    MENUCONFIG_COLOR.  To select a theme use::
+
+        make MENUCONFIG_COLOR=<theme> menuconfig
+
+    Available themes are::
+
+      - mono       => selects colors suitable for monochrome displays
+      - blackbg    => selects a color scheme with black background
+      - classic    => theme with blue background. The classic look
+      - bluetitle  => a LCD friendly version of classic. (default)
+
+``MENUCONFIG_MODE``
+    This mode shows all sub-menus in one large tree.
+
+    Example::
+
+        make MENUCONFIG_MODE=single_menu menuconfig
+
+
+nconfig
+=======
+
+nconfig is an alternate text-based configurator.  It lists function
+keys across the bottom of the terminal (window) that execute commands.
+You can also just use the corresponding numeric key to execute the
+commands unless you are in a data entry window.  E.g., instead of F6
+for Save, you can just press 6.
+
+Use F1 for Global help or F3 for the Short help menu.
+
+Searching in nconfig:
+
+    You can search either in the menu entry "prompt" strings
+    or in the configuration symbols.
+
+    Use / to begin a search through the menu entries.  This does
+    not support regular expressions.  Use <Down> or <Up> for
+    Next hit and Previous hit, respectively.  Use <Esc> to
+    terminate the search mode.
+
+    F8 (SymSearch) searches the configuration symbols for the
+    given string or regular expression (regex).
+
+    In the SymSearch, pressing the key in the (#) prefix will
+    jump directly to that location. You will be returned to the
+    current search results after exiting this new menu.
+
+Environment variables:
+
+``NCONFIG_MODE``
+    This mode shows all sub-menus in one large tree.
+
+    Example::
+
+        make NCONFIG_MODE=single_menu nconfig
+
+
+xconfig
+=======
+
+Searching in xconfig:
+
+    The Search function searches for kernel configuration symbol
+    names, so you have to know something close to what you are
+    looking for.
+
+    Example::
+
+        Ctrl-F hotplug
+
+    or::
+
+        Menu: File, Search, hotplug
+
+    lists all config symbol entries that contain "hotplug" in
+    the symbol name.  In this Search dialog, you may change the
+    config setting for any of the entries that are not grayed out.
+    You can also enter a different search string without having
+    to return to the main menu.
+
+
+gconfig
+=======
+
+Searching in gconfig:
+
+    There is no search command in gconfig.  However, gconfig does
+    have several different viewing choices, modes, and options.
diff --git a/Documentation/kbuild/llvm.rst b/Documentation/kbuild/llvm.rst
new file mode 100644
index 000000000..441d8786f
--- /dev/null
+++ b/Documentation/kbuild/llvm.rst
@@ -0,0 +1,221 @@
+.. _kbuild_llvm:
+
+==============================
+Building Linux with Clang/LLVM
+==============================
+
+This document covers how to build the Linux kernel with Clang and LLVM
+utilities.
+
+About
+-----
+
+The Linux kernel has always traditionally been compiled with GNU toolchains
+such as GCC and binutils. Ongoing work has allowed for `Clang
+<https://clang.llvm.org/>`_ and `LLVM <https://llvm.org/>`_ utilities to be
+used as viable substitutes. Distributions such as `Android
+<https://www.android.com/>`_, `ChromeOS
+<https://www.chromium.org/chromium-os>`_, `OpenMandriva
+<https://www.openmandriva.org/>`_, and `Chimera Linux
+<https://chimera-linux.org/>`_ use Clang built kernels. Google's and Meta's
+datacenter fleets also run kernels built with Clang.
+
+`LLVM is a collection of toolchain components implemented in terms of C++
+objects <https://www.aosabook.org/en/llvm.html>`_. Clang is a front-end to LLVM
+that supports C and the GNU C extensions required by the kernel, and is
+pronounced "klang," not "see-lang."
+
+Building with LLVM
+------------------
+
+Invoke ``make`` via::
+
+	make LLVM=1
+
+to compile for the host target. For cross compiling::
+
+	make LLVM=1 ARCH=arm64
+
+The LLVM= argument
+------------------
+
+LLVM has substitutes for GNU binutils utilities. They can be enabled
+individually. The full list of supported make variables::
+
+	make CC=clang LD=ld.lld AR=llvm-ar NM=llvm-nm STRIP=llvm-strip \
+	  OBJCOPY=llvm-objcopy OBJDUMP=llvm-objdump READELF=llvm-readelf \
+	  HOSTCC=clang HOSTCXX=clang++ HOSTAR=llvm-ar HOSTLD=ld.lld
+
+``LLVM=1`` expands to the above.
+
+If your LLVM tools are not available in your PATH, you can supply their
+location using the LLVM variable with a trailing slash::
+
+	make LLVM=/path/to/llvm/
+
+which will use ``/path/to/llvm/clang``, ``/path/to/llvm/ld.lld``, etc. The
+following may also be used::
+
+	PATH=/path/to/llvm:$PATH make LLVM=1
+
+If your LLVM tools have a version suffix and you want to test with that
+explicit version rather than the unsuffixed executables like ``LLVM=1``, you
+can pass the suffix using the ``LLVM`` variable::
+
+	make LLVM=-14
+
+which will use ``clang-14``, ``ld.lld-14``, etc.
+
+To support combinations of out of tree paths with version suffixes, we
+recommend::
+
+	PATH=/path/to/llvm/:$PATH make LLVM=-14
+
+The same value used for ``LLVM=`` should be set for each invocation of ``make``
+if configuring and building via distinct commands. ``LLVM=`` should also be set
+as an environment variable when running scripts that will eventually run
+``make``.
+
+Cross Compiling
+---------------
+
+A single Clang compiler binary (and corresponding LLVM utilities) will
+typically contain all supported back ends, which can help simplify cross
+compiling especially when ``LLVM=1`` is used. If you use only LLVM tools,
+``CROSS_COMPILE`` or target-triple-prefixes become unnecessary. Example::
+
+	make LLVM=1 ARCH=arm64
+
+As an example of mixing LLVM and GNU utilities, for a target like ``ARCH=s390``
+which does not yet have ``ld.lld`` or ``llvm-objcopy`` support, you could
+invoke ``make`` via::
+
+	make LLVM=1 ARCH=s390 LD=s390x-linux-gnu-ld.bfd \
+	  OBJCOPY=s390x-linux-gnu-objcopy
+
+This example will invoke ``s390x-linux-gnu-ld.bfd`` as the linker and
+``s390x-linux-gnu-objcopy``, so ensure those are reachable in your ``$PATH``.
+
+``CROSS_COMPILE`` is not used to prefix the Clang compiler binary (or
+corresponding LLVM utilities) as is the case for GNU utilities when ``LLVM=1``
+is not set.
+
+The LLVM_IAS= argument
+----------------------
+
+Clang can assemble assembler code. You can pass ``LLVM_IAS=0`` to disable this
+behavior and have Clang invoke the corresponding non-integrated assembler
+instead. Example::
+
+	make LLVM=1 LLVM_IAS=0
+
+``CROSS_COMPILE`` is necessary when cross compiling and ``LLVM_IAS=0``
+is used in order to set ``--prefix=`` for the compiler to find the
+corresponding non-integrated assembler (typically, you don't want to use the
+system assembler when targeting another architecture). Example::
+
+	make LLVM=1 ARCH=arm LLVM_IAS=0 CROSS_COMPILE=arm-linux-gnueabi-
+
+
+Ccache
+------
+
+``ccache`` can be used with ``clang`` to improve subsequent builds, (though
+KBUILD_BUILD_TIMESTAMP_ should be set to a deterministic value between builds
+in order to avoid 100% cache misses, see Reproducible_builds_ for more info)::
+
+	KBUILD_BUILD_TIMESTAMP='' make LLVM=1 CC="ccache clang"
+
+.. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp
+.. _Reproducible_builds: reproducible-builds.html#timestamps
+
+Supported Architectures
+-----------------------
+
+LLVM does not target all of the architectures that Linux supports and
+just because a target is supported in LLVM does not mean that the kernel
+will build or work without any issues. Below is a general summary of
+architectures that currently work with ``CC=clang`` or ``LLVM=1``. Level
+of support corresponds to "S" values in the MAINTAINERS files. If an
+architecture is not present, it either means that LLVM does not target
+it or there are known issues. Using the latest stable version of LLVM or
+even the development tree will generally yield the best results.
+An architecture's ``defconfig`` is generally expected to work well,
+certain configurations may have problems that have not been uncovered
+yet. Bug reports are always welcome at the issue tracker below!
+
+.. list-table::
+   :widths: 10 10 10
+   :header-rows: 1
+
+   * - Architecture
+     - Level of support
+     - ``make`` command
+   * - arm
+     - Supported
+     - ``LLVM=1``
+   * - arm64
+     - Supported
+     - ``LLVM=1``
+   * - hexagon
+     - Maintained
+     - ``LLVM=1``
+   * - loongarch
+     - Maintained
+     - ``LLVM=1``
+   * - mips
+     - Maintained
+     - ``LLVM=1``
+   * - powerpc
+     - Maintained
+     - ``LLVM=1``
+   * - riscv
+     - Supported
+     - ``LLVM=1``
+   * - s390
+     - Maintained
+     - ``LLVM=1`` (LLVM >= 18.1.0), ``CC=clang`` (LLVM < 18.1.0)
+   * - sparc (sparc64 only)
+     - Maintained
+     - ``CC=clang LLVM_IAS=0`` (LLVM >= 20)
+   * - um (User Mode)
+     - Maintained
+     - ``LLVM=1``
+   * - x86
+     - Supported
+     - ``LLVM=1``
+
+Getting Help
+------------
+
+- `Website <https://clangbuiltlinux.github.io/>`_
+- `Mailing List <https://lore.kernel.org/llvm/>`_: <llvm@lists.linux.dev>
+- `Old Mailing List Archives <https://groups.google.com/g/clang-built-linux>`_
+- `Issue Tracker <https://github.com/ClangBuiltLinux/linux/issues>`_
+- IRC: #clangbuiltlinux on irc.libera.chat
+- `Telegram <https://t.me/ClangBuiltLinux>`_: @ClangBuiltLinux
+- `Wiki <https://github.com/ClangBuiltLinux/linux/wiki>`_
+- `Beginner Bugs <https://github.com/ClangBuiltLinux/linux/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22>`_
+
+.. _getting_llvm:
+
+Getting LLVM
+-------------
+
+We provide prebuilt stable versions of LLVM on `kernel.org
+<https://kernel.org/pub/tools/llvm/>`_. These have been optimized with profile
+data for building Linux kernels, which should improve kernel build times
+relative to other distributions of LLVM.
+
+Below are links that may be useful for building LLVM from source or procuring
+it through a distribution's package manager.
+
+- https://releases.llvm.org/download.html
+- https://github.com/llvm/llvm-project
+- https://llvm.org/docs/GettingStarted.html
+- https://llvm.org/docs/CMake.html
+- https://apt.llvm.org/
+- https://www.archlinux.org/packages/extra/x86_64/llvm/
+- https://github.com/ClangBuiltLinux/tc-build
+- https://github.com/ClangBuiltLinux/linux/wiki/Building-Clang-from-source
+- https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/
diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst
new file mode 100644
index 000000000..7521cae7d
--- /dev/null
+++ b/Documentation/kbuild/makefiles.rst
@@ -0,0 +1,1723 @@
+======================
+Linux Kernel Makefiles
+======================
+
+This document describes the Linux kernel Makefiles.
+
+Overview
+========
+
+The Makefiles have five parts::
+
+	Makefile                    the top Makefile.
+	.config                     the kernel configuration file.
+	arch/$(SRCARCH)/Makefile    the arch Makefile.
+	scripts/Makefile.*          common rules etc. for all kbuild Makefiles.
+	kbuild Makefiles            exist in every subdirectory
+
+The top Makefile reads the .config file, which comes from the kernel
+configuration process.
+
+The top Makefile is responsible for building two major products: vmlinux
+(the resident kernel image) and modules (any module files).
+It builds these goals by recursively descending into the subdirectories of
+the kernel source tree.
+
+The list of subdirectories which are visited depends upon the kernel
+configuration. The top Makefile textually includes an arch Makefile
+with the name arch/$(SRCARCH)/Makefile. The arch Makefile supplies
+architecture-specific information to the top Makefile.
+
+Each subdirectory has a kbuild Makefile which carries out the commands
+passed down from above. The kbuild Makefile uses information from the
+.config file to construct various file lists used by kbuild to build
+any built-in or modular targets.
+
+scripts/Makefile.* contains all the definitions/rules etc. that
+are used to build the kernel based on the kbuild makefiles.
+
+Who does what
+=============
+
+People have four different relationships with the kernel Makefiles.
+
+*Users* are people who build kernels.  These people type commands such as
+``make menuconfig`` or ``make``.  They usually do not read or edit
+any kernel Makefiles (or any other source files).
+
+*Normal developers* are people who work on features such as device
+drivers, file systems, and network protocols.  These people need to
+maintain the kbuild Makefiles for the subsystem they are
+working on.  In order to do this effectively, they need some overall
+knowledge about the kernel Makefiles, plus detailed knowledge about the
+public interface for kbuild.
+
+*Arch developers* are people who work on an entire architecture, such
+as sparc or x86.  Arch developers need to know about the arch Makefile
+as well as kbuild Makefiles.
+
+*Kbuild developers* are people who work on the kernel build system itself.
+These people need to know about all aspects of the kernel Makefiles.
+
+This document is aimed towards normal developers and arch developers.
+
+
+The kbuild files
+================
+
+Most Makefiles within the kernel are kbuild Makefiles that use the
+kbuild infrastructure. This chapter introduces the syntax used in the
+kbuild makefiles.
+
+The preferred name for the kbuild files are ``Makefile`` but ``Kbuild`` can
+be used and if both a ``Makefile`` and a ``Kbuild`` file exists, then the ``Kbuild``
+file will be used.
+
+Section `Goal definitions`_ is a quick intro; further chapters provide
+more details, with real examples.
+
+Goal definitions
+----------------
+
+Goal definitions are the main part (heart) of the kbuild Makefile.
+These lines define the files to be built, any special compilation
+options, and any subdirectories to be entered recursively.
+
+The most simple kbuild makefile contains one line:
+
+Example::
+
+  obj-y += foo.o
+
+This tells kbuild that there is one object in that directory, named
+foo.o. foo.o will be built from foo.c or foo.S.
+
+If foo.o shall be built as a module, the variable obj-m is used.
+Therefore the following pattern is often used:
+
+Example::
+
+  obj-$(CONFIG_FOO) += foo.o
+
+$(CONFIG_FOO) evaluates to either y (for built-in) or m (for module).
+If CONFIG_FOO is neither y nor m, then the file will not be compiled
+nor linked.
+
+Built-in object goals - obj-y
+-----------------------------
+
+The kbuild Makefile specifies object files for vmlinux
+in the $(obj-y) lists.  These lists depend on the kernel
+configuration.
+
+Kbuild compiles all the $(obj-y) files.  It then calls
+``$(AR) rcSTP`` to merge these files into one built-in.a file.
+This is a thin archive without a symbol table. It will be later
+linked into vmlinux by scripts/link-vmlinux.sh
+
+The order of files in $(obj-y) is significant.  Duplicates in
+the lists are allowed: the first instance will be linked into
+built-in.a and succeeding instances will be ignored.
+
+Link order is significant, because certain functions
+(module_init() / __initcall) will be called during boot in the
+order they appear. So keep in mind that changing the link
+order may e.g. change the order in which your SCSI
+controllers are detected, and thus your disks are renumbered.
+
+Example::
+
+  #drivers/isdn/i4l/Makefile
+  # Makefile for the kernel ISDN subsystem and device drivers.
+  # Each configuration option enables a list of files.
+  obj-$(CONFIG_ISDN_I4L)         += isdn.o
+  obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+Loadable module goals - obj-m
+-----------------------------
+
+$(obj-m) specifies object files which are built as loadable
+kernel modules.
+
+A module may be built from one source file or several source
+files. In the case of one source file, the kbuild makefile
+simply adds the file to $(obj-m).
+
+Example::
+
+  #drivers/isdn/i4l/Makefile
+  obj-$(CONFIG_ISDN_PPP_BSDCOMP) += isdn_bsdcomp.o
+
+Note: In this example $(CONFIG_ISDN_PPP_BSDCOMP) evaluates to "m"
+
+If a kernel module is built from several source files, you specify
+that you want to build a module in the same way as above; however,
+kbuild needs to know which object files you want to build your
+module from, so you have to tell it by setting a $(<module_name>-y)
+variable.
+
+Example::
+
+  #drivers/isdn/i4l/Makefile
+  obj-$(CONFIG_ISDN_I4L) += isdn.o
+  isdn-y := isdn_net_lib.o isdn_v110.o isdn_common.o
+
+In this example, the module name will be isdn.o. Kbuild will
+compile the objects listed in $(isdn-y) and then run
+``$(LD) -r`` on the list of these files to generate isdn.o.
+
+Due to kbuild recognizing $(<module_name>-y) for composite objects,
+you can use the value of a ``CONFIG_`` symbol to optionally include an
+object file as part of a composite object.
+
+Example::
+
+  #fs/ext2/Makefile
+  obj-$(CONFIG_EXT2_FS) += ext2.o
+  ext2-y := balloc.o dir.o file.o ialloc.o inode.o ioctl.o \
+    namei.o super.o symlink.o
+  ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o xattr_user.o \
+    xattr_trusted.o
+
+In this example, xattr.o, xattr_user.o and xattr_trusted.o are only
+part of the composite object ext2.o if $(CONFIG_EXT2_FS_XATTR)
+evaluates to "y".
+
+Note: Of course, when you are building objects into the kernel,
+the syntax above will also work. So, if you have CONFIG_EXT2_FS=y,
+kbuild will build an ext2.o file for you out of the individual
+parts and then link this into built-in.a, as you would expect.
+
+Library file goals - lib-y
+--------------------------
+
+Objects listed with obj-* are used for modules, or
+combined in a built-in.a for that specific directory.
+There is also the possibility to list objects that will
+be included in a library, lib.a.
+All objects listed with lib-y are combined in a single
+library for that directory.
+Objects that are listed in obj-y and additionally listed in
+lib-y will not be included in the library, since they will
+be accessible anyway.
+For consistency, objects listed in lib-m will be included in lib.a.
+
+Note that the same kbuild makefile may list files to be built-in
+and to be part of a library. Therefore the same directory
+may contain both a built-in.a and a lib.a file.
+
+Example::
+
+  #arch/x86/lib/Makefile
+  lib-y    := delay.o
+
+This will create a library lib.a based on delay.o. For kbuild to
+actually recognize that there is a lib.a being built, the directory
+shall be listed in libs-y.
+
+See also `List directories to visit when descending`_.
+
+Use of lib-y is normally restricted to ``lib/`` and ``arch/*/lib``.
+
+Descending down in directories
+------------------------------
+
+A Makefile is only responsible for building objects in its own
+directory. Files in subdirectories should be taken care of by
+Makefiles in these subdirs. The build system will automatically
+invoke make recursively in subdirectories, provided you let it know of
+them.
+
+To do so, obj-y and obj-m are used.
+ext2 lives in a separate directory, and the Makefile present in fs/
+tells kbuild to descend down using the following assignment.
+
+Example::
+
+  #fs/Makefile
+  obj-$(CONFIG_EXT2_FS) += ext2/
+
+If CONFIG_EXT2_FS is set to either "y" (built-in) or "m" (modular)
+the corresponding obj- variable will be set, and kbuild will descend
+down in the ext2 directory.
+
+Kbuild uses this information not only to decide that it needs to visit
+the directory, but also to decide whether or not to link objects from
+the directory into vmlinux.
+
+When Kbuild descends into the directory with "y", all built-in objects
+from that directory are combined into the built-in.a, which will be
+eventually linked into vmlinux.
+
+When Kbuild descends into the directory with "m", in contrast, nothing
+from that directory will be linked into vmlinux. If the Makefile in
+that directory specifies obj-y, those objects will be left orphan.
+It is very likely a bug of the Makefile or of dependencies in Kconfig.
+
+Kbuild also supports dedicated syntax, subdir-y and subdir-m, for
+descending into subdirectories. It is a good fit when you know they
+do not contain kernel-space objects at all. A typical usage is to let
+Kbuild descend into subdirectories to build tools.
+
+Examples::
+
+  # scripts/Makefile
+  subdir-$(CONFIG_GCC_PLUGINS) += gcc-plugins
+  subdir-$(CONFIG_MODVERSIONS) += genksyms
+  subdir-$(CONFIG_SECURITY_SELINUX) += selinux
+
+Unlike obj-y/m, subdir-y/m does not need the trailing slash since this
+syntax is always used for directories.
+
+It is good practice to use a ``CONFIG_`` variable when assigning directory
+names. This allows kbuild to totally skip the directory if the
+corresponding ``CONFIG_`` option is neither "y" nor "m".
+
+Non-builtin vmlinux targets - extra-y
+-------------------------------------
+
+extra-y specifies targets which are needed for building vmlinux,
+but not combined into built-in.a.
+
+Examples are:
+
+1) vmlinux linker script
+
+   The linker script for vmlinux is located at
+   arch/$(SRCARCH)/kernel/vmlinux.lds
+
+Example::
+
+  # arch/x86/kernel/Makefile
+  extra-y	+= vmlinux.lds
+
+extra-y is now deprecated because this is equivalent to:
+
+  always-$(KBUILD_BUILTIN) += vmlinux.lds
+
+$(extra-y) should only contain targets needed for vmlinux.
+
+Kbuild skips extra-y when vmlinux is apparently not a final goal.
+(e.g. ``make modules``, or building external modules)
+
+If you intend to build targets unconditionally, always-y (explained
+in the next section) is the correct syntax to use.
+
+Always built goals - always-y
+-----------------------------
+
+always-y specifies targets which are literally always built when
+Kbuild visits the Makefile.
+
+Example::
+
+  # ./Kbuild
+  offsets-file := include/generated/asm-offsets.h
+  always-y += $(offsets-file)
+
+Compilation flags
+-----------------
+
+ccflags-y, asflags-y and ldflags-y
+  These three flags apply only to the kbuild makefile in which they
+  are assigned. They are used for all the normal cc, as and ld
+  invocations happening during a recursive build.
+
+  ccflags-y specifies options for compiling with $(CC).
+
+  Example::
+
+    # drivers/acpi/acpica/Makefile
+    ccflags-y				:= -Os -D_LINUX -DBUILDING_ACPICA
+    ccflags-$(CONFIG_ACPI_DEBUG)	+= -DACPI_DEBUG_OUTPUT
+
+  This variable is necessary because the top Makefile owns the
+  variable $(KBUILD_CFLAGS) and uses it for compilation flags for the
+  entire tree.
+
+  asflags-y specifies assembler options.
+
+  Example::
+
+    #arch/sparc/kernel/Makefile
+    asflags-y := -ansi
+
+  ldflags-y specifies options for linking with $(LD).
+
+  Example::
+
+    #arch/cris/boot/compressed/Makefile
+    ldflags-y += -T $(src)/decompress_$(arch-y).lds
+
+subdir-ccflags-y, subdir-asflags-y
+  The two flags listed above are similar to ccflags-y and asflags-y.
+  The difference is that the subdir- variants have effect for the kbuild
+  file where they are present and all subdirectories.
+  Options specified using subdir-* are added to the commandline before
+  the options specified using the non-subdir variants.
+
+  Example::
+
+    subdir-ccflags-y := -Werror
+
+ccflags-remove-y, asflags-remove-y
+  These flags are used to remove particular flags for the compiler,
+  assembler invocations.
+
+  Example::
+
+    ccflags-remove-$(CONFIG_MCOUNT) += -pg
+
+CFLAGS_$@, AFLAGS_$@
+  CFLAGS_$@ and AFLAGS_$@ only apply to commands in current
+  kbuild makefile.
+
+  $(CFLAGS_$@) specifies per-file options for $(CC).  The $@
+  part has a literal value which specifies the file that it is for.
+
+  CFLAGS_$@ has the higher priority than ccflags-remove-y; CFLAGS_$@
+  can re-add compiler flags that were removed by ccflags-remove-y.
+
+  Example::
+
+    # drivers/scsi/Makefile
+    CFLAGS_aha152x.o =   -DAHA152X_STAT -DAUTOCONF
+
+  This line specify compilation flags for aha152x.o.
+
+  $(AFLAGS_$@) is a similar feature for source files in assembly
+  languages.
+
+  AFLAGS_$@ has the higher priority than asflags-remove-y; AFLAGS_$@
+  can re-add assembler flags that were removed by asflags-remove-y.
+
+  Example::
+
+    # arch/arm/kernel/Makefile
+    AFLAGS_head.o        := -DTEXT_OFFSET=$(TEXT_OFFSET)
+    AFLAGS_crunch-bits.o := -Wa,-mcpu=ep9312
+    AFLAGS_iwmmxt.o      := -Wa,-mcpu=iwmmxt
+
+Dependency tracking
+-------------------
+
+Kbuild tracks dependencies on the following:
+
+1) All prerequisite files (both ``*.c`` and ``*.h``)
+2) ``CONFIG_`` options used in all prerequisite files
+3) Command-line used to compile target
+
+Thus, if you change an option to $(CC) all affected files will
+be re-compiled.
+
+Custom Rules
+------------
+
+Custom rules are used when the kbuild infrastructure does
+not provide the required support. A typical example is
+header files generated during the build process.
+Another example are the architecture-specific Makefiles which
+need custom rules to prepare boot images etc.
+
+Custom rules are written as normal Make rules.
+Kbuild is not executing in the directory where the Makefile is
+located, so all custom rules shall use a relative
+path to prerequisite files and target files.
+
+Two variables are used when defining custom rules:
+
+$(src)
+  $(src) is the directory where the Makefile is located. Always use $(src) when
+  referring to files located in the src tree.
+
+$(obj)
+  $(obj) is the directory where the target is saved. Always use $(obj) when
+  referring to generated files. Use $(obj) for pattern rules that need to work
+  for both generated files and real sources (VPATH will help to find the
+  prerequisites not only in the object tree but also in the source tree).
+
+  Example::
+
+    #drivers/scsi/Makefile
+    $(obj)/53c8xx_d.h: $(src)/53c7,8xx.scr $(src)/script_asm.pl
+    $(CPP) -DCHIP=810 - < $< | ... $(src)/script_asm.pl
+
+  This is a custom rule, following the normal syntax
+  required by make.
+
+  The target file depends on two prerequisite files. References
+  to the target file are prefixed with $(obj), references
+  to prerequisites are referenced with $(src) (because they are not
+  generated files).
+
+$(srcroot)
+  $(srcroot) refers to the root of the source you are building, which can be
+  either the kernel source or the external modules source, depending on whether
+  KBUILD_EXTMOD is set. This can be either a relative or an absolute path, but
+  if KBUILD_ABS_SRCTREE=1 is set, it is always an absolute path.
+
+$(srctree)
+  $(srctree) refers to the root of the kernel source tree. When building the
+  kernel, this is the same as $(srcroot).
+
+$(objtree)
+  $(objtree) refers to the root of the kernel object tree. It is ``.`` when
+  building the kernel, but it is different when building external modules.
+
+$(kecho)
+  echoing information to user in a rule is often a good practice
+  but when execution ``make -s`` one does not expect to see any output
+  except for warnings/errors.
+  To support this kbuild defines $(kecho) which will echo out the
+  text following $(kecho) to stdout except if ``make -s`` is used.
+
+  Example::
+
+    # arch/arm/Makefile
+    $(BOOT_TARGETS): vmlinux
+            $(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@
+            @$(kecho) '  Kernel: $(boot)/$@ is ready'
+
+  When kbuild is executing with KBUILD_VERBOSE unset, then only a shorthand
+  of a command is normally displayed.
+  To enable this behaviour for custom commands kbuild requires
+  two variables to be set::
+
+    quiet_cmd_<command> - what shall be echoed
+          cmd_<command> - the command to execute
+
+  Example::
+
+    # lib/Makefile
+    quiet_cmd_crc32 = GEN     $@
+          cmd_crc32 = $< > $@
+
+    $(obj)/crc32table.h: $(obj)/gen_crc32table
+            $(call cmd,crc32)
+
+  When updating the $(obj)/crc32table.h target, the line::
+
+    GEN     lib/crc32table.h
+
+  will be displayed with ``make KBUILD_VERBOSE=``.
+
+Command change detection
+------------------------
+
+When the rule is evaluated, timestamps are compared between the target
+and its prerequisite files. GNU Make updates the target when any of the
+prerequisites is newer than that.
+
+The target should be rebuilt also when the command line has changed
+since the last invocation. This is not supported by Make itself, so
+Kbuild achieves this by a kind of meta-programming.
+
+if_changed is the macro used for this purpose, in the following form::
+
+  quiet_cmd_<command> = ...
+        cmd_<command> = ...
+
+  <target>: <source(s)> FORCE
+          $(call if_changed,<command>)
+
+Any target that utilizes if_changed must be listed in $(targets),
+otherwise the command line check will fail, and the target will
+always be built.
+
+If the target is already listed in the recognized syntax such as
+obj-y/m, lib-y/m, extra-y/m, always-y/m, hostprogs, userprogs, Kbuild
+automatically adds it to $(targets). Otherwise, the target must be
+explicitly added to $(targets).
+
+Assignments to $(targets) are without $(obj)/ prefix. if_changed may be
+used in conjunction with custom rules as defined in `Custom Rules`_.
+
+Note: It is a typical mistake to forget the FORCE prerequisite.
+Another common pitfall is that whitespace is sometimes significant; for
+instance, the below will fail (note the extra space after the comma)::
+
+  target: source(s) FORCE
+
+**WRONG!**	$(call if_changed, objcopy)
+
+Note:
+  if_changed should not be used more than once per target.
+  It stores the executed command in a corresponding .cmd
+  file and multiple calls would result in overwrites and
+  unwanted results when the target is up to date and only the
+  tests on changed commands trigger execution of commands.
+
+$(CC) support functions
+-----------------------
+
+The kernel may be built with several different versions of
+$(CC), each supporting a unique set of features and options.
+kbuild provides basic support to check for valid options for $(CC).
+$(CC) is usually the gcc compiler, but other alternatives are
+available.
+
+as-option
+  as-option is used to check if $(CC) -- when used to compile
+  assembler (``*.S``) files -- supports the given option. An optional
+  second option may be specified if the first option is not supported.
+
+  Example::
+
+    #arch/sh/Makefile
+    cflags-y += $(call as-option,-Wa$(comma)-isa=$(isa-y),)
+
+  In the above example, cflags-y will be assigned the option
+  -Wa$(comma)-isa=$(isa-y) if it is supported by $(CC).
+  The second argument is optional, and if supplied will be used
+  if first argument is not supported.
+
+as-instr
+  as-instr checks if the assembler reports a specific instruction
+  and then outputs either option1 or option2
+  C escapes are supported in the test instruction
+  Note: as-instr-option uses KBUILD_AFLAGS for assembler options
+
+cc-option
+  cc-option is used to check if $(CC) supports a given option, and if
+  not supported to use an optional second option.
+
+  Example::
+
+    #arch/x86/Makefile
+    cflags-y += $(call cc-option,-march=pentium-mmx,-march=i586)
+
+  In the above example, cflags-y will be assigned the option
+  -march=pentium-mmx if supported by $(CC), otherwise -march=i586.
+  The second argument to cc-option is optional, and if omitted,
+  cflags-y will be assigned no value if first option is not supported.
+  Note: cc-option uses KBUILD_CFLAGS for $(CC) options
+
+cc-option-yn
+  cc-option-yn is used to check if $(CC) supports a given option
+  and return "y" if supported, otherwise "n".
+
+  Example::
+
+    #arch/ppc/Makefile
+    biarch := $(call cc-option-yn, -m32)
+    aflags-$(biarch) += -a32
+    cflags-$(biarch) += -m32
+
+  In the above example, $(biarch) is set to y if $(CC) supports the -m32
+  option. When $(biarch) equals "y", the expanded variables $(aflags-y)
+  and $(cflags-y) will be assigned the values -a32 and -m32,
+  respectively.
+
+  Note: cc-option-yn uses KBUILD_CFLAGS for $(CC) options
+
+cc-disable-warning
+  cc-disable-warning checks if $(CC) supports a given warning and returns
+  the commandline switch to disable it. This special function is needed,
+  because gcc 4.4 and later accept any unknown -Wno-* option and only
+  warn about it if there is another warning in the source file.
+
+  Example::
+
+    KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
+
+  In the above example, -Wno-unused-but-set-variable will be added to
+  KBUILD_CFLAGS only if $(CC) really accepts it.
+
+gcc-min-version
+  gcc-min-version tests if the value of $(CONFIG_GCC_VERSION) is greater than
+  or equal to the provided value and evaluates to y if so.
+
+  Example::
+
+    cflags-$(call gcc-min-version, 110100) := -foo
+
+  In this example, cflags-y will be assigned the value -foo if $(CC) is gcc and
+  $(CONFIG_GCC_VERSION) is >= 11.1.
+
+clang-min-version
+  clang-min-version tests if the value of $(CONFIG_CLANG_VERSION) is greater
+  than or equal to the provided value and evaluates to y if so.
+
+  Example::
+
+    cflags-$(call clang-min-version, 110000) := -foo
+
+  In this example, cflags-y will be assigned the value -foo if $(CC) is clang
+  and $(CONFIG_CLANG_VERSION) is >= 11.0.0.
+
+cc-cross-prefix
+  cc-cross-prefix is used to check if there exists a $(CC) in path with
+  one of the listed prefixes. The first prefix where there exist a
+  prefix$(CC) in the PATH is returned - and if no prefix$(CC) is found
+  then nothing is returned.
+
+  Additional prefixes are separated by a single space in the
+  call of cc-cross-prefix.
+
+  This functionality is useful for architecture Makefiles that try
+  to set CROSS_COMPILE to well-known values but may have several
+  values to select between.
+
+  It is recommended only to try to set CROSS_COMPILE if it is a cross
+  build (host arch is different from target arch). And if CROSS_COMPILE
+  is already set then leave it with the old value.
+
+  Example::
+
+    #arch/m68k/Makefile
+    ifneq ($(SUBARCH),$(ARCH))
+            ifeq ($(CROSS_COMPILE),)
+                    CROSS_COMPILE := $(call cc-cross-prefix, m68k-linux-gnu-)
+            endif
+    endif
+
+$(RUSTC) support functions
+--------------------------
+
+rustc-min-version
+  rustc-min-version tests if the value of $(CONFIG_RUSTC_VERSION) is greater
+  than or equal to the provided value and evaluates to y if so.
+
+  Example::
+
+    rustflags-$(call rustc-min-version, 108500) := -Cfoo
+
+  In this example, rustflags-y will be assigned the value -Cfoo if
+  $(CONFIG_RUSTC_VERSION) is >= 1.85.0.
+
+$(LD) support functions
+-----------------------
+
+ld-option
+  ld-option is used to check if $(LD) supports the supplied option.
+  ld-option takes two options as arguments.
+
+  The second argument is an optional option that can be used if the
+  first option is not supported by $(LD).
+
+  Example::
+
+    #Makefile
+    LDFLAGS_vmlinux += $(call ld-option, -X)
+
+Script invocation
+-----------------
+
+Make rules may invoke scripts to build the kernel. The rules shall
+always provide the appropriate interpreter to execute the script. They
+shall not rely on the execute bits being set, and shall not invoke the
+script directly. For the convenience of manual script invocation, such
+as invoking ./scripts/checkpatch.pl, it is recommended to set execute
+bits on the scripts nonetheless.
+
+Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL),
+and $(PYTHON3) to refer to interpreters for the respective
+scripts.
+
+Example::
+
+  #Makefile
+  cmd_depmod = $(CONFIG_SHELL) $(srctree)/scripts/depmod.sh $(DEPMOD) \
+          $(KERNELRELEASE)
+
+Host Program support
+====================
+
+Kbuild supports building executables on the host for use during the
+compilation stage.
+
+Two steps are required in order to use a host executable.
+
+The first step is to tell kbuild that a host program exists. This is
+done utilising the variable ``hostprogs``.
+
+The second step is to add an explicit dependency to the executable.
+This can be done in two ways. Either add the dependency in a rule,
+or utilise the variable ``always-y``.
+Both possibilities are described in the following.
+
+Simple Host Program
+-------------------
+
+In some cases there is a need to compile and run a program on the
+computer where the build is running.
+
+The following line tells kbuild that the program bin2hex shall be
+built on the build host.
+
+Example::
+
+  hostprogs := bin2hex
+
+Kbuild assumes in the above example that bin2hex is made from a single
+c-source file named bin2hex.c located in the same directory as
+the Makefile.
+
+Composite Host Programs
+-----------------------
+
+Host programs can be made up based on composite objects.
+The syntax used to define composite objects for host programs is
+similar to the syntax used for kernel objects.
+$(<executable>-objs) lists all objects used to link the final
+executable.
+
+Example::
+
+  #scripts/lxdialog/Makefile
+  hostprogs     := lxdialog
+  lxdialog-objs := checklist.o lxdialog.o
+
+Objects with extension .o are compiled from the corresponding .c
+files. In the above example, checklist.c is compiled to checklist.o
+and lxdialog.c is compiled to lxdialog.o.
+
+Finally, the two .o files are linked to the executable, lxdialog.
+Note: The syntax <executable>-y is not permitted for host-programs.
+
+Using C++ for host programs
+---------------------------
+
+kbuild offers support for host programs written in C++. This was
+introduced solely to support kconfig, and is not recommended
+for general use.
+
+Example::
+
+  #scripts/kconfig/Makefile
+  hostprogs     := qconf
+  qconf-cxxobjs := qconf.o
+
+In the example above the executable is composed of the C++ file
+qconf.cc - identified by $(qconf-cxxobjs).
+
+If qconf is composed of a mixture of .c and .cc files, then an
+additional line can be used to identify this.
+
+Example::
+
+  #scripts/kconfig/Makefile
+  hostprogs     := qconf
+  qconf-cxxobjs := qconf.o
+  qconf-objs    := check.o
+
+Using Rust for host programs
+----------------------------
+
+Kbuild offers support for host programs written in Rust. However,
+since a Rust toolchain is not mandatory for kernel compilation,
+it may only be used in scenarios where Rust is required to be
+available (e.g. when  ``CONFIG_RUST`` is enabled).
+
+Example::
+
+  hostprogs     := target
+  target-rust   := y
+
+Kbuild will compile ``target`` using ``target.rs`` as the crate root,
+located in the same directory as the ``Makefile``. The crate may
+consist of several source files (see ``samples/rust/hostprogs``).
+
+Controlling compiler options for host programs
+----------------------------------------------
+
+When compiling host programs, it is possible to set specific flags.
+The programs will always be compiled utilising $(HOSTCC) passed
+the options specified in $(KBUILD_HOSTCFLAGS).
+
+To set flags that will take effect for all host programs created
+in that Makefile, use the variable HOST_EXTRACFLAGS.
+
+Example::
+
+  #scripts/lxdialog/Makefile
+  HOST_EXTRACFLAGS += -I/usr/include/ncurses
+
+To set specific flags for a single file the following construction
+is used:
+
+Example::
+
+  #arch/ppc64/boot/Makefile
+  HOSTCFLAGS_piggyback.o := -DKERNELBASE=$(KERNELBASE)
+
+It is also possible to specify additional options to the linker.
+
+Example::
+
+  #scripts/kconfig/Makefile
+  HOSTLDLIBS_qconf := -L$(QTDIR)/lib
+
+When linking qconf, it will be passed the extra option
+``-L$(QTDIR)/lib``.
+
+When host programs are actually built
+-------------------------------------
+
+Kbuild will only build host-programs when they are referenced
+as a prerequisite.
+
+This is possible in two ways:
+
+(1) List the prerequisite explicitly in a custom rule.
+
+    Example::
+
+      #drivers/pci/Makefile
+      hostprogs := gen-devlist
+      $(obj)/devlist.h: $(src)/pci.ids $(obj)/gen-devlist
+      ( cd $(obj); ./gen-devlist ) < $<
+
+    The target $(obj)/devlist.h will not be built before
+    $(obj)/gen-devlist is updated. Note that references to
+    the host programs in custom rules must be prefixed with $(obj).
+
+(2) Use always-y
+
+    When there is no suitable custom rule, and the host program
+    shall be built when a makefile is entered, the always-y
+    variable shall be used.
+
+    Example::
+
+      #scripts/lxdialog/Makefile
+      hostprogs     := lxdialog
+      always-y      := $(hostprogs)
+
+    Kbuild provides the following shorthand for this::
+
+      hostprogs-always-y := lxdialog
+
+    This will tell kbuild to build lxdialog even if not referenced in
+    any rule.
+
+Userspace Program support
+=========================
+
+Just like host programs, Kbuild also supports building userspace executables
+for the target architecture (i.e. the same architecture as you are building
+the kernel for).
+
+The syntax is quite similar. The difference is to use ``userprogs`` instead of
+``hostprogs``.
+
+Simple Userspace Program
+------------------------
+
+The following line tells kbuild that the program bpf-direct shall be
+built for the target architecture.
+
+Example::
+
+  userprogs := bpf-direct
+
+Kbuild assumes in the above example that bpf-direct is made from a
+single C source file named bpf-direct.c located in the same directory
+as the Makefile.
+
+Composite Userspace Programs
+----------------------------
+
+Userspace programs can be made up based on composite objects.
+The syntax used to define composite objects for userspace programs is
+similar to the syntax used for kernel objects.
+$(<executable>-objs) lists all objects used to link the final
+executable.
+
+Example::
+
+  #samples/seccomp/Makefile
+  userprogs      := bpf-fancy
+  bpf-fancy-objs := bpf-fancy.o bpf-helper.o
+
+Objects with extension .o are compiled from the corresponding .c
+files. In the above example, bpf-fancy.c is compiled to bpf-fancy.o
+and bpf-helper.c is compiled to bpf-helper.o.
+
+Finally, the two .o files are linked to the executable, bpf-fancy.
+Note: The syntax <executable>-y is not permitted for userspace programs.
+
+Controlling compiler options for userspace programs
+---------------------------------------------------
+
+When compiling userspace programs, it is possible to set specific flags.
+The programs will always be compiled utilising $(CC) passed
+the options specified in $(KBUILD_USERCFLAGS).
+
+To set flags that will take effect for all userspace programs created
+in that Makefile, use the variable userccflags.
+
+Example::
+
+  # samples/seccomp/Makefile
+  userccflags += -I usr/include
+
+To set specific flags for a single file the following construction
+is used:
+
+Example::
+
+  bpf-helper-userccflags += -I user/include
+
+It is also possible to specify additional options to the linker.
+
+Example::
+
+  # net/bpfilter/Makefile
+  bpfilter_umh-userldflags += -static
+
+To specify libraries linked to a userspace program, you can use
+``<executable>-userldlibs``. The ``userldlibs`` syntax specifies libraries
+linked to all userspace programs created in the current Makefile.
+
+When linking bpfilter_umh, it will be passed the extra option -static.
+
+From command line, :ref:`USERCFLAGS and USERLDFLAGS <userkbuildflags>` will also be used.
+
+When userspace programs are actually built
+------------------------------------------
+
+Kbuild builds userspace programs only when told to do so.
+There are two ways to do this.
+
+(1) Add it as the prerequisite of another file
+
+    Example::
+
+      #net/bpfilter/Makefile
+      userprogs := bpfilter_umh
+      $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh
+
+    $(obj)/bpfilter_umh is built before $(obj)/bpfilter_umh_blob.o
+
+(2) Use always-y
+
+    Example::
+
+      userprogs := binderfs_example
+      always-y := $(userprogs)
+
+    Kbuild provides the following shorthand for this::
+
+      userprogs-always-y := binderfs_example
+
+    This will tell Kbuild to build binderfs_example when it visits this
+    Makefile.
+
+Kbuild clean infrastructure
+===========================
+
+``make clean`` deletes most generated files in the obj tree where the kernel
+is compiled. This includes generated files such as host programs.
+Kbuild knows targets listed in $(hostprogs), $(always-y), $(always-m),
+$(always-), $(extra-y), $(extra-) and $(targets). They are all deleted
+during ``make clean``. Files matching the patterns ``*.[oas]``, ``*.ko``, plus
+some additional files generated by kbuild are deleted all over the kernel
+source tree when ``make clean`` is executed.
+
+Additional files or directories can be specified in kbuild makefiles by use of
+$(clean-files).
+
+Example::
+
+  #lib/Makefile
+  clean-files := crc32table.h
+
+When executing ``make clean``, the file ``crc32table.h`` will be deleted.
+Kbuild will assume files to be in the same relative directory as the
+Makefile.
+
+To exclude certain files or directories from make clean, use the
+$(no-clean-files) variable.
+
+Usually kbuild descends down in subdirectories due to ``obj-* := dir/``,
+but in the architecture makefiles where the kbuild infrastructure
+is not sufficient this sometimes needs to be explicit.
+
+Example::
+
+  #arch/x86/boot/Makefile
+  subdir- := compressed
+
+The above assignment instructs kbuild to descend down in the
+directory compressed/ when ``make clean`` is executed.
+
+Note 1: arch/$(SRCARCH)/Makefile cannot use ``subdir-``, because that file is
+included in the top level makefile. Instead, arch/$(SRCARCH)/Kbuild can use
+``subdir-``.
+
+Note 2: All directories listed in core-y, libs-y, drivers-y and net-y will
+be visited during ``make clean``.
+
+Architecture Makefiles
+======================
+
+The top level Makefile sets up the environment and does the preparation,
+before starting to descend down in the individual directories.
+
+The top level makefile contains the generic part, whereas
+arch/$(SRCARCH)/Makefile contains what is required to set up kbuild
+for said architecture.
+
+To do so, arch/$(SRCARCH)/Makefile sets up a number of variables and defines
+a few targets.
+
+When kbuild executes, the following steps are followed (roughly):
+
+1) Configuration of the kernel => produce .config
+
+2) Store kernel version in include/linux/version.h
+
+3) Updating all other prerequisites to the target prepare:
+
+   - Additional prerequisites are specified in arch/$(SRCARCH)/Makefile
+
+4) Recursively descend down in all directories listed in
+   init-* core* drivers-* net-* libs-* and build all targets.
+
+   - The values of the above variables are expanded in arch/$(SRCARCH)/Makefile.
+
+5) All object files are then linked and the resulting file vmlinux is
+   located at the root of the obj tree.
+   The very first objects linked are listed in scripts/head-object-list.txt.
+
+6) Finally, the architecture-specific part does any required post processing
+   and builds the final bootimage.
+
+   - This includes building boot records
+   - Preparing initrd images and the like
+
+Set variables to tweak the build to the architecture
+----------------------------------------------------
+
+KBUILD_LDFLAGS
+  Generic $(LD) options
+
+  Flags used for all invocations of the linker.
+  Often specifying the emulation is sufficient.
+
+  Example::
+
+    #arch/s390/Makefile
+    KBUILD_LDFLAGS         := -m elf_s390
+
+  Note: ldflags-y can be used to further customise
+  the flags used. See `Non-builtin vmlinux targets - extra-y`_.
+
+LDFLAGS_vmlinux
+  Options for $(LD) when linking vmlinux
+
+  LDFLAGS_vmlinux is used to specify additional flags to pass to
+  the linker when linking the final vmlinux image.
+
+  LDFLAGS_vmlinux uses the LDFLAGS_$@ support.
+
+  Example::
+
+    #arch/x86/Makefile
+    LDFLAGS_vmlinux := -e stext
+
+OBJCOPYFLAGS
+  objcopy flags
+
+  When $(call if_changed,objcopy) is used to translate a .o file,
+  the flags specified in OBJCOPYFLAGS will be used.
+
+  $(call if_changed,objcopy) is often used to generate raw binaries on
+  vmlinux.
+
+  Example::
+
+    #arch/s390/Makefile
+    OBJCOPYFLAGS := -O binary
+
+    #arch/s390/boot/Makefile
+    $(obj)/image: vmlinux FORCE
+            $(call if_changed,objcopy)
+
+  In this example, the binary $(obj)/image is a binary version of
+  vmlinux. The usage of $(call if_changed,xxx) will be described later.
+
+KBUILD_AFLAGS
+  Assembler flags
+
+  Default value - see top level Makefile.
+
+  Append or modify as required per architecture.
+
+  Example::
+
+    #arch/sparc64/Makefile
+    KBUILD_AFLAGS += -m64 -mcpu=ultrasparc
+
+KBUILD_CFLAGS
+  $(CC) compiler flags
+
+  Default value - see top level Makefile.
+
+  Append or modify as required per architecture.
+
+  Often, the KBUILD_CFLAGS variable depends on the configuration.
+
+  Example::
+
+    #arch/x86/boot/compressed/Makefile
+    cflags-$(CONFIG_X86_32) := -march=i386
+    cflags-$(CONFIG_X86_64) := -mcmodel=small
+    KBUILD_CFLAGS += $(cflags-y)
+
+  Many arch Makefiles dynamically run the target C compiler to
+  probe supported options::
+
+    #arch/x86/Makefile
+
+    ...
+    cflags-$(CONFIG_MPENTIUMII)     += $(call cc-option,\
+						-march=pentium2,-march=i686)
+    ...
+    # Disable unit-at-a-time mode ...
+    KBUILD_CFLAGS += $(call cc-option,-fno-unit-at-a-time)
+    ...
+
+
+  The first example utilises the trick that a config option expands
+  to "y" when selected.
+
+KBUILD_RUSTFLAGS
+  $(RUSTC) compiler flags
+
+  Default value - see top level Makefile.
+
+  Append or modify as required per architecture.
+
+  Often, the KBUILD_RUSTFLAGS variable depends on the configuration.
+
+  Note that target specification file generation (for ``--target``)
+  is handled in ``scripts/generate_rust_target.rs``.
+
+KBUILD_AFLAGS_KERNEL
+  Assembler options specific for built-in
+
+  $(KBUILD_AFLAGS_KERNEL) contains extra C compiler flags used to compile
+  resident kernel code.
+
+KBUILD_AFLAGS_MODULE
+  Assembler options specific for modules
+
+  $(KBUILD_AFLAGS_MODULE) is used to add arch-specific options that
+  are used for assembler.
+
+  From commandline AFLAGS_MODULE shall be used (see kbuild.rst).
+
+KBUILD_CFLAGS_KERNEL
+  $(CC) options specific for built-in
+
+  $(KBUILD_CFLAGS_KERNEL) contains extra C compiler flags used to compile
+  resident kernel code.
+
+KBUILD_CFLAGS_MODULE
+  Options for $(CC) when building modules
+
+  $(KBUILD_CFLAGS_MODULE) is used to add arch-specific options that
+  are used for $(CC).
+
+  From commandline CFLAGS_MODULE shall be used (see kbuild.rst).
+
+KBUILD_RUSTFLAGS_KERNEL
+  $(RUSTC) options specific for built-in
+
+  $(KBUILD_RUSTFLAGS_KERNEL) contains extra Rust compiler flags used to
+  compile resident kernel code.
+
+KBUILD_RUSTFLAGS_MODULE
+  Options for $(RUSTC) when building modules
+
+  $(KBUILD_RUSTFLAGS_MODULE) is used to add arch-specific options that
+  are used for $(RUSTC).
+
+  From commandline RUSTFLAGS_MODULE shall be used (see kbuild.rst).
+
+KBUILD_LDFLAGS_MODULE
+  Options for $(LD) when linking modules
+
+  $(KBUILD_LDFLAGS_MODULE) is used to add arch-specific options
+  used when linking modules. This is often a linker script.
+
+  From commandline LDFLAGS_MODULE shall be used (see kbuild.rst).
+
+KBUILD_LDS
+  The linker script with full path. Assigned by the top-level Makefile.
+
+KBUILD_VMLINUX_OBJS
+  All object files for vmlinux. They are linked to vmlinux in the same
+  order as listed in KBUILD_VMLINUX_OBJS.
+
+  The objects listed in scripts/head-object-list.txt are exceptions;
+  they are placed before the other objects.
+
+KBUILD_VMLINUX_LIBS
+  All .a ``lib`` files for vmlinux. KBUILD_VMLINUX_OBJS and
+  KBUILD_VMLINUX_LIBS together specify all the object files used to
+  link vmlinux.
+
+Add prerequisites to archheaders
+--------------------------------
+
+The archheaders: rule is used to generate header files that
+may be installed into user space by ``make headers_install``.
+
+It is run before ``make archprepare`` when run on the
+architecture itself.
+
+Add prerequisites to archprepare
+--------------------------------
+
+The archprepare: rule is used to list prerequisites that need to be
+built before starting to descend down in the subdirectories.
+
+This is usually used for header files containing assembler constants.
+
+Example::
+
+  #arch/arm/Makefile
+  archprepare: maketools
+
+In this example, the file target maketools will be processed
+before descending down in the subdirectories.
+
+Generating offset header files
+------------------------------
+
+The ``include/generated/asm-offsets.h`` header exposes C structure
+member offsets and other compile-time constants to assembly code. It
+is generated from ``arch/$(SRCARCH)/kernel/asm-offsets.c``.
+
+The source file uses ``DEFINE()``, ``OFFSET()``, ``BLANK()`` and
+``COMMENT()`` from ``<linux/kbuild.h>``. These emit marker strings
+through inline asm that Kbuild extracts from the compiled assembly
+output.
+
+Example::
+
+  #include <linux/kbuild.h>
+  #include <linux/sched.h>
+
+  int main(void)
+  {
+          OFFSET(TSK_ACTIVE_MM, task_struct, active_mm);
+          DEFINE(THREAD_SIZE, THREAD_SIZE);
+          BLANK();
+          return 0;
+  }
+
+The rules are defined in the top-level ``Kbuild`` and
+``scripts/Makefile.lib``. The header is built during Kbuild's
+``prepare`` phase, after ``archprepare`` and before descending into
+subdirectories.
+
+The same mechanism generates ``include/generated/bounds.h`` from
+``kernel/bounds.c`` and ``include/generated/rq-offsets.h`` from
+``kernel/sched/rq-offsets.c``.
+
+List directories to visit when descending
+-----------------------------------------
+
+An arch Makefile cooperates with the top Makefile to define variables
+which specify how to build the vmlinux file.  Note that there is no
+corresponding arch-specific section for modules; the module-building
+machinery is all architecture-independent.
+
+core-y, libs-y, drivers-y
+  $(libs-y) lists directories where a lib.a archive can be located.
+
+  The rest list directories where a built-in.a object file can be
+  located.
+
+  Then the rest follows in this order:
+
+    $(core-y), $(libs-y), $(drivers-y)
+
+  The top level Makefile defines values for all generic directories,
+  and arch/$(SRCARCH)/Makefile only adds architecture-specific
+  directories.
+
+  Example::
+
+    # arch/sparc/Makefile
+    core-y                 += arch/sparc/
+
+    libs-y                 += arch/sparc/prom/
+    libs-y                 += arch/sparc/lib/
+
+    drivers-$(CONFIG_PM) += arch/sparc/power/
+
+Architecture-specific boot images
+---------------------------------
+
+An arch Makefile specifies goals that take the vmlinux file, compress
+it, wrap it in bootstrapping code, and copy the resulting files
+somewhere. This includes various kinds of installation commands.
+The actual goals are not standardized across architectures.
+
+It is common to locate any additional processing in a boot/
+directory below arch/$(SRCARCH)/.
+
+Kbuild does not provide any smart way to support building a
+target specified in boot/. Therefore arch/$(SRCARCH)/Makefile shall
+call make manually to build a target in boot/.
+
+The recommended approach is to include shortcuts in
+arch/$(SRCARCH)/Makefile, and use the full path when calling down
+into the arch/$(SRCARCH)/boot/Makefile.
+
+Example::
+
+  #arch/x86/Makefile
+  boot := arch/x86/boot
+  bzImage: vmlinux
+          $(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
+
+``$(Q)$(MAKE) $(build)=<dir>`` is the recommended way to invoke
+make in a subdirectory.
+
+There are no rules for naming architecture-specific targets,
+but executing ``make help`` will list all relevant targets.
+To support this, $(archhelp) must be defined.
+
+Example::
+
+  #arch/x86/Makefile
+  define archhelp
+    echo  '* bzImage      - Compressed kernel image (arch/x86/boot/bzImage)'
+  endif
+
+When make is executed without arguments, the first goal encountered
+will be built. In the top level Makefile the first goal present
+is all:.
+
+An architecture shall always, per default, build a bootable image.
+In ``make help``, the default goal is highlighted with a ``*``.
+
+Add a new prerequisite to all: to select a default goal different
+from vmlinux.
+
+Example::
+
+  #arch/x86/Makefile
+  all: bzImage
+
+When ``make`` is executed without arguments, bzImage will be built.
+
+Commands useful for building a boot image
+-----------------------------------------
+
+Kbuild provides a few macros that are useful when building a
+boot image.
+
+ld
+  Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
+
+  Example::
+
+    #arch/x86/boot/Makefile
+    LDFLAGS_bootsect := -Ttext 0x0 -s --oformat binary
+    LDFLAGS_setup    := -Ttext 0x0 -s --oformat binary -e begtext
+
+    targets += setup setup.o bootsect bootsect.o
+    $(obj)/setup $(obj)/bootsect: %: %.o FORCE
+            $(call if_changed,ld)
+
+  In this example, there are two possible targets, requiring different
+  options to the linker. The linker options are specified using the
+  LDFLAGS_$@ syntax - one for each potential target.
+
+  $(targets) are assigned all potential targets, by which kbuild knows
+  the targets and will:
+
+  1) check for commandline changes
+  2) delete target during make clean
+
+  The ``: %: %.o`` part of the prerequisite is a shorthand that
+  frees us from listing the setup.o and bootsect.o files.
+
+  Note:
+  It is a common mistake to forget the ``targets :=`` assignment,
+  resulting in the target file being recompiled for no
+  obvious reason.
+
+objcopy
+  Copy binary. Uses OBJCOPYFLAGS usually specified in
+  arch/$(SRCARCH)/Makefile.
+
+  OBJCOPYFLAGS_$@ may be used to set additional options.
+
+gzip
+  Compress target. Use maximum compression to compress target.
+
+  Example::
+
+    #arch/x86/boot/compressed/Makefile
+    $(obj)/vmlinux.bin.gz: $(vmlinux.bin.all-y) FORCE
+            $(call if_changed,gzip)
+
+dtc
+  Create flattened device tree blob object suitable for linking
+  into vmlinux. Device tree blobs linked into vmlinux are placed
+  in an init section in the image. Platform code *must* copy the
+  blob to non-init memory prior to calling unflatten_device_tree().
+
+  To use this command, simply add ``*.dtb`` into obj-y or targets, or make
+  some other target depend on ``%.dtb``
+
+  A central rule exists to create ``$(obj)/%.dtb`` from ``$(src)/%.dts``;
+  architecture Makefiles do no need to explicitly write out that rule.
+
+  Example::
+
+    targets += $(dtb-y)
+    DTC_FLAGS ?= -p 1024
+
+Preprocessing linker scripts
+----------------------------
+
+When the vmlinux image is built, the linker script
+arch/$(SRCARCH)/kernel/vmlinux.lds is used.
+
+The script is a preprocessed variant of the file vmlinux.lds.S
+located in the same directory.
+
+kbuild knows .lds files and includes a rule ``*lds.S`` -> ``*lds``.
+
+Example::
+
+  #arch/x86/kernel/Makefile
+  extra-y := vmlinux.lds
+
+The assignment to extra-y is used to tell kbuild to build the
+target vmlinux.lds.
+
+The assignment to $(CPPFLAGS_vmlinux.lds) tells kbuild to use the
+specified options when building the target vmlinux.lds.
+
+When building the ``*.lds`` target, kbuild uses the variables::
+
+  KBUILD_CPPFLAGS      : Set in top-level Makefile
+  cppflags-y           : May be set in the kbuild makefile
+  CPPFLAGS_$(@F)       : Target-specific flags.
+                         Note that the full filename is used in this
+                         assignment.
+
+The kbuild infrastructure for ``*lds`` files is used in several
+architecture-specific files.
+
+Generic header files
+--------------------
+
+The directory include/asm-generic contains the header files
+that may be shared between individual architectures.
+
+The recommended approach how to use a generic header file is
+to list the file in the Kbuild file.
+
+See `generic-y`_ for further info on syntax etc.
+
+Post-link pass
+--------------
+
+If the file arch/xxx/Makefile.postlink exists, this makefile
+will be invoked for post-link objects (vmlinux and modules.ko)
+for architectures to run post-link passes on. Must also handle
+the clean target.
+
+This pass runs after kallsyms generation. If the architecture
+needs to modify symbol locations, rather than manipulate the
+kallsyms, it may be easier to add another postlink target for
+.tmp_vmlinux? targets to be called from link-vmlinux.sh.
+
+For example, powerpc uses this to check relocation sanity of
+the linked vmlinux file.
+
+Kbuild syntax for exported headers
+==================================
+
+The kernel includes a set of headers that is exported to userspace.
+Many headers can be exported as-is but other headers require a
+minimal pre-processing before they are ready for user-space.
+
+The pre-processing does:
+
+- drop kernel-specific annotations
+- drop include of compiler.h
+- drop all sections that are kernel internal (guarded by ``ifdef __KERNEL__``)
+
+All headers under include/uapi/, include/generated/uapi/,
+arch/<arch>/include/uapi/ and arch/<arch>/include/generated/uapi/
+are exported.
+
+A Kbuild file may be defined under arch/<arch>/include/uapi/asm/ and
+arch/<arch>/include/asm/ to list asm files coming from asm-generic.
+
+See subsequent chapter for the syntax of the Kbuild file.
+
+no-export-headers
+-----------------
+
+no-export-headers is essentially used by include/uapi/linux/Kbuild to
+avoid exporting specific headers (e.g. kvm.h) on architectures that do
+not support it. It should be avoided as much as possible.
+
+generic-y
+---------
+
+If an architecture uses a verbatim copy of a header from
+include/asm-generic then this is listed in the file
+arch/$(SRCARCH)/include/asm/Kbuild like this:
+
+Example::
+
+  #arch/x86/include/asm/Kbuild
+  generic-y += termios.h
+  generic-y += rtc.h
+
+During the prepare phase of the build a wrapper include
+file is generated in the directory::
+
+  arch/$(SRCARCH)/include/generated/asm
+
+When a header is exported where the architecture uses
+the generic header a similar wrapper is generated as part
+of the set of exported headers in the directory::
+
+  usr/include/asm
+
+The generated wrapper will in both cases look like the following:
+
+Example: termios.h::
+
+  #include <asm-generic/termios.h>
+
+generated-y
+-----------
+
+If an architecture generates other header files alongside generic-y
+wrappers, generated-y specifies them.
+
+This prevents them being treated as stale asm-generic wrappers and
+removed.
+
+Example::
+
+  #arch/x86/include/asm/Kbuild
+  generated-y += syscalls_32.h
+
+mandatory-y
+-----------
+
+mandatory-y is essentially used by include/(uapi/)asm-generic/Kbuild
+to define the minimum set of ASM headers that all architectures must have.
+
+This works like optional generic-y. If a mandatory header is missing
+in arch/$(SRCARCH)/include/(uapi/)/asm, Kbuild will automatically
+generate a wrapper of the asm-generic one.
+
+Kbuild Variables
+================
+
+The top Makefile exports the following variables:
+
+VERSION, PATCHLEVEL, SUBLEVEL, EXTRAVERSION
+  These variables define the current kernel version.  A few arch
+  Makefiles actually use these values directly; they should use
+  $(KERNELRELEASE) instead.
+
+  $(VERSION), $(PATCHLEVEL), and $(SUBLEVEL) define the basic
+  three-part version number, such as "2", "4", and "0".  These three
+  values are always numeric.
+
+  $(EXTRAVERSION) defines an even tinier sublevel for pre-patches
+  or additional patches.	It is usually some non-numeric string
+  such as "-pre4", and is often blank.
+
+KERNELRELEASE
+  $(KERNELRELEASE) is a single string such as "2.4.0-pre4", suitable
+  for constructing installation directory names or showing in
+  version strings.  Some arch Makefiles use it for this purpose.
+
+ARCH
+  This variable defines the target architecture, such as "i386",
+  "arm", or "sparc". Some kbuild Makefiles test $(ARCH) to
+  determine which files to compile.
+
+  By default, the top Makefile sets $(ARCH) to be the same as the
+  host system architecture.  For a cross build, a user may
+  override the value of $(ARCH) on the command line::
+
+    make ARCH=m68k ...
+
+SRCARCH
+  This variable specifies the directory in arch/ to build.
+
+  ARCH and SRCARCH may not necessarily match. A couple of arch
+  directories are biarch, that is, a single ``arch/*/`` directory supports
+  both 32-bit and 64-bit.
+
+  For example, you can pass in ARCH=i386, ARCH=x86_64, or ARCH=x86.
+  For all of them, SRCARCH=x86 because arch/x86/ supports both i386 and
+  x86_64.
+
+INSTALL_PATH
+  This variable defines a place for the arch Makefiles to install
+  the resident kernel image and System.map file.
+  Use this for architecture-specific install targets.
+
+INSTALL_MOD_PATH, MODLIB
+  $(INSTALL_MOD_PATH) specifies a prefix to $(MODLIB) for module
+  installation.  This variable is not defined in the Makefile but
+  may be passed in by the user if desired.
+
+  $(MODLIB) specifies the directory for module installation.
+  The top Makefile defines $(MODLIB) to
+  $(INSTALL_MOD_PATH)/lib/modules/$(KERNELRELEASE).  The user may
+  override this value on the command line if desired.
+
+INSTALL_MOD_STRIP
+  If this variable is specified, it will cause modules to be stripped
+  after they are installed.  If INSTALL_MOD_STRIP is "1", then the
+  default option --strip-debug will be used.  Otherwise, the
+  INSTALL_MOD_STRIP value will be used as the option(s) to the strip
+  command.
+
+INSTALL_DTBS_PATH
+  This variable specifies a prefix for relocations required by build
+  roots. It defines a place for installing the device tree blobs. Like
+  INSTALL_MOD_PATH, it isn't defined in the Makefile, but can be passed
+  by the user if desired. Otherwise it defaults to the kernel install
+  path.
+
+Makefile language
+=================
+
+The kernel Makefiles are designed to be run with GNU Make.  The Makefiles
+use only the documented features of GNU Make, but they do use many
+GNU extensions.
+
+GNU Make supports elementary list-processing functions.  The kernel
+Makefiles use a novel style of list building and manipulation with few
+``if`` statements.
+
+GNU Make has two assignment operators, ``:=`` and ``=``.  ``:=`` performs
+immediate evaluation of the right-hand side and stores an actual string
+into the left-hand side.  ``=`` is like a formula definition; it stores the
+right-hand side in an unevaluated form and then evaluates this form each
+time the left-hand side is used.
+
+There are some cases where ``=`` is appropriate.  Usually, though, ``:=``
+is the right choice.
+
+Credits
+=======
+
+- Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net>
+- Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de>
+- Updates by Sam Ravnborg <sam@ravnborg.org>
+- Language QA by Jan Engelhardt <jengelh@gmx.de>
diff --git a/Documentation/kbuild/modules.rst b/Documentation/kbuild/modules.rst
new file mode 100644
index 000000000..b3a26a36e
--- /dev/null
+++ b/Documentation/kbuild/modules.rst
@@ -0,0 +1,513 @@
+=========================
+Building External Modules
+=========================
+
+This document describes how to build an out-of-tree kernel module.
+
+Introduction
+============
+
+"kbuild" is the build system used by the Linux kernel. Modules must use
+kbuild to stay compatible with changes in the build infrastructure and
+to pick up the right flags to the compiler. Functionality for building modules
+both in-tree and out-of-tree is provided. The method for building
+either is similar, and all modules are initially developed and built
+out-of-tree.
+
+Covered in this document is information aimed at developers interested
+in building out-of-tree (or "external") modules. The author of an
+external module should supply a makefile that hides most of the
+complexity, so one only has to type "make" to build the module. This is
+easily accomplished, and a complete example will be presented in
+section `Creating a Kbuild File for an External Module`_.
+
+
+How to Build External Modules
+=============================
+
+To build external modules, you must have a prebuilt kernel available
+that contains the configuration and header files used in the build.
+Also, the kernel must have been built with modules enabled. If you are
+using a distribution kernel, there will be a package for the kernel you
+are running provided by your distribution.
+
+An alternative is to use the "make" target "modules_prepare." This will
+make sure the kernel contains the information required. The target
+exists solely as a simple way to prepare a kernel source tree for
+building external modules.
+
+NOTE: "modules_prepare" will not build Module.symvers even if
+CONFIG_MODVERSIONS is set; therefore, a full kernel build needs to be
+executed to make module versioning work.
+
+Command Syntax
+--------------
+
+	The command to build an external module is::
+
+		$ make -C <path_to_kernel_dir> M=$PWD
+
+	The kbuild system knows that an external module is being built
+	due to the "M=<dir>" option given in the command.
+
+	To build against the running kernel use::
+
+		$ make -C /lib/modules/`uname -r`/build M=$PWD
+
+	Then to install the module(s) just built, add the target
+	"modules_install" to the command::
+
+		$ make -C /lib/modules/`uname -r`/build M=$PWD modules_install
+
+	Starting from Linux 6.13, you can use the -f option instead of -C. This
+	will avoid unnecessary change of the working directory. The external
+	module will be output to the directory where you invoke make.
+
+		$ make -f /lib/modules/`uname -r`/build/Makefile M=$PWD
+
+Options
+-------
+
+	($KDIR refers to the path of the kernel source directory, or the path
+	of the kernel output directory if the kernel was built in a separate
+	build directory.)
+
+	You can optionally pass MO= option if you want to build the modules in
+	a separate directory.
+
+	make -C $KDIR M=$PWD [MO=$BUILD_DIR]
+
+	-C $KDIR
+		The directory that contains the kernel and relevant build
+		artifacts used for building an external module.
+		"make" will actually change to the specified directory
+		when executing and will change back when finished.
+
+	M=$PWD
+		Informs kbuild that an external module is being built.
+		The value given to "M" is the absolute path of the
+		directory where the external module (kbuild file) is
+		located.
+
+	MO=$BUILD_DIR
+		Specifies a separate output directory for the external module.
+
+Targets
+-------
+
+	When building an external module, only a subset of the "make"
+	targets are available.
+
+	make -C $KDIR M=$PWD [target]
+
+	The default will build the module(s) located in the current
+	directory, so a target does not need to be specified. All
+	output files will also be generated in this directory. No
+	attempts are made to update the kernel source, and it is a
+	precondition that a successful "make" has been executed for the
+	kernel.
+
+	modules
+		The default target for external modules. It has the
+		same functionality as if no target was specified. See
+		description above.
+
+	modules_install
+		Install the external module(s). The default location is
+		/lib/modules/<kernel_release>/updates/, but a prefix may
+		be added with INSTALL_MOD_PATH (discussed in section
+		`Module Installation`_).
+
+	clean
+		Remove all generated files in the module directory only.
+
+	help
+		List the available targets for external modules.
+
+Building Separate Files
+-----------------------
+
+	It is possible to build single files that are part of a module.
+	This works equally well for the kernel, a module, and even for
+	external modules.
+
+	Example (The module foo.ko, consist of bar.o and baz.o)::
+
+		make -C $KDIR M=$PWD bar.lst
+		make -C $KDIR M=$PWD baz.o
+		make -C $KDIR M=$PWD foo.ko
+		make -C $KDIR M=$PWD ./
+
+
+Creating a Kbuild File for an External Module
+=============================================
+
+In the last section we saw the command to build a module for the
+running kernel. The module is not actually built, however, because a
+build file is required. Contained in this file will be the name of
+the module(s) being built, along with the list of requisite source
+files. The file may be as simple as a single line::
+
+	obj-m := <module_name>.o
+
+The kbuild system will build <module_name>.o from <module_name>.c,
+and, after linking, will result in the kernel module <module_name>.ko.
+The above line can be put in either a "Kbuild" file or a "Makefile."
+When the module is built from multiple sources, an additional line is
+needed listing the files::
+
+	<module_name>-y := <src1>.o <src2>.o ...
+
+NOTE: Further documentation describing the syntax used by kbuild is
+located in Documentation/kbuild/makefiles.rst.
+
+The examples below demonstrate how to create a build file for the
+module 8123.ko, which is built from the following files::
+
+	8123_if.c
+	8123_if.h
+	8123_pci.c
+
+Shared Makefile
+---------------
+
+	An external module always includes a wrapper makefile that
+	supports building the module using "make" with no arguments.
+	This target is not used by kbuild; it is only for convenience.
+	Additional functionality, such as test targets, can be included
+	but should be filtered out from kbuild due to possible name
+	clashes.
+
+	Example 1::
+
+		--> filename: Makefile
+		ifneq ($(KERNELRELEASE),)
+		# kbuild part of makefile
+		obj-m  := 8123.o
+		8123-y := 8123_if.o 8123_pci.o
+
+		else
+		# normal makefile
+		KDIR ?= /lib/modules/`uname -r`/build
+
+		default:
+			$(MAKE) -C $(KDIR) M=$$PWD
+
+		endif
+
+	The check for KERNELRELEASE is used to separate the two parts
+	of the makefile. In the example, kbuild will only see the two
+	assignments, whereas "make" will see everything except these
+	two assignments. This is due to two passes made on the file:
+	the first pass is by the "make" instance run on the command
+	line; the second pass is by the kbuild system, which is
+	initiated by the parameterized "make" in the default target.
+
+Separate Kbuild File and Makefile
+---------------------------------
+
+	Kbuild will first look for a file named "Kbuild", and if it is not
+	found, it will then look for "Makefile". Utilizing a "Kbuild" file
+	allows us to split up the "Makefile" from example 1 into two files:
+
+	Example 2::
+
+		--> filename: Kbuild
+		obj-m  := 8123.o
+		8123-y := 8123_if.o 8123_pci.o
+
+		--> filename: Makefile
+		KDIR ?= /lib/modules/`uname -r`/build
+
+		default:
+			$(MAKE) -C $(KDIR) M=$$PWD
+
+	The split in example 2 is questionable due to the simplicity of
+	each file; however, some external modules use makefiles
+	consisting of several hundred lines, and here it really pays
+	off to separate the kbuild part from the rest.
+
+	Linux 6.13 and later support another way. The external module Makefile
+	can include the kernel Makefile directly, rather than invoking sub Make.
+
+	Example 3::
+
+		--> filename: Kbuild
+		obj-m  := 8123.o
+		8123-y := 8123_if.o 8123_pci.o
+
+		--> filename: Makefile
+		KDIR ?= /lib/modules/$(shell uname -r)/build
+		export KBUILD_EXTMOD := $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
+		include $(KDIR)/Makefile
+
+
+Building Multiple Modules
+-------------------------
+
+	kbuild supports building multiple modules with a single build
+	file. For example, if you wanted to build two modules, foo.ko
+	and bar.ko, the kbuild lines would be::
+
+		obj-m := foo.o bar.o
+		foo-y := <foo_srcs>
+		bar-y := <bar_srcs>
+
+	It is that simple!
+
+
+Include Files
+=============
+
+Within the kernel, header files are kept in standard locations
+according to the following rule:
+
+	* If the header file only describes the internal interface of a
+	  module, then the file is placed in the same directory as the
+	  source files.
+	* If the header file describes an interface used by other parts
+	  of the kernel that are located in different directories, then
+	  the file is placed in include/linux/.
+
+	  NOTE:
+	      There are two notable exceptions to this rule: larger
+	      subsystems have their own directory under include/, such as
+	      include/scsi; and architecture specific headers are located
+	      under arch/$(SRCARCH)/include/.
+
+Kernel Includes
+---------------
+
+	To include a header file located under include/linux/, simply
+	use::
+
+		#include <linux/module.h>
+
+	kbuild will add options to the compiler so the relevant directories
+	are searched.
+
+Single Subdirectory
+-------------------
+
+	External modules tend to place header files in a separate
+	include/ directory where their source is located, although this
+	is not the usual kernel style. To inform kbuild of the
+	directory, use either ccflags-y or CFLAGS_<filename>.o.
+
+	Using the example from section 3, if we moved 8123_if.h to a
+	subdirectory named include, the resulting kbuild file would
+	look like::
+
+		--> filename: Kbuild
+		obj-m := 8123.o
+
+		ccflags-y := -I $(src)/include
+		8123-y := 8123_if.o 8123_pci.o
+
+Several Subdirectories
+----------------------
+
+	kbuild can handle files that are spread over several directories.
+	Consider the following example::
+
+		.
+		|__ src
+		|   |__ complex_main.c
+		|   |__ hal
+		|	|__ hardwareif.c
+		|	|__ include
+		|	    |__ hardwareif.h
+		|__ include
+			|__ complex.h
+
+	To build the module complex.ko, we then need the following
+	kbuild file::
+
+		--> filename: Kbuild
+		obj-m := complex.o
+		complex-y := src/complex_main.o
+		complex-y += src/hal/hardwareif.o
+
+		ccflags-y := -I$(src)/include
+		ccflags-y += -I$(src)/src/hal/include
+
+	As you can see, kbuild knows how to handle object files located
+	in other directories. The trick is to specify the directory
+	relative to the kbuild file's location. That being said, this
+	is NOT recommended practice.
+
+	For the header files, kbuild must be explicitly told where to
+	look. When kbuild executes, the current directory is always the
+	root of the kernel tree (the argument to "-C") and therefore an
+	absolute path is needed. $(src) provides the absolute path by
+	pointing to the directory where the currently executing kbuild
+	file is located.
+
+
+Module Installation
+===================
+
+Modules which are included in the kernel are installed in the
+directory:
+
+	/lib/modules/$(KERNELRELEASE)/kernel/
+
+And external modules are installed in:
+
+	/lib/modules/$(KERNELRELEASE)/updates/
+
+INSTALL_MOD_PATH
+----------------
+
+	Above are the default directories but as always some level of
+	customization is possible. A prefix can be added to the
+	installation path using the variable INSTALL_MOD_PATH::
+
+		$ make INSTALL_MOD_PATH=/frodo modules_install
+		=> Install dir: /frodo/lib/modules/$(KERNELRELEASE)/kernel/
+
+	INSTALL_MOD_PATH may be set as an ordinary shell variable or,
+	as shown above, can be specified on the command line when
+	calling "make." This has effect when installing both in-tree
+	and out-of-tree modules.
+
+INSTALL_MOD_DIR
+---------------
+
+	External modules are by default installed to a directory under
+	/lib/modules/$(KERNELRELEASE)/updates/, but you may wish to
+	locate modules for a specific functionality in a separate
+	directory. For this purpose, use INSTALL_MOD_DIR to specify an
+	alternative name to "updates."::
+
+		$ make INSTALL_MOD_DIR=gandalf -C $KDIR \
+		       M=$PWD modules_install
+		=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf/
+
+
+Module Versioning
+=================
+
+Module versioning is enabled by the CONFIG_MODVERSIONS tag, and is used
+as a simple ABI consistency check. A CRC value of the full prototype
+for an exported symbol is created. When a module is loaded/used, the
+CRC values contained in the kernel are compared with similar values in
+the module; if they are not equal, the kernel refuses to load the
+module.
+
+Module.symvers contains a list of all exported symbols from a kernel
+build.
+
+Symbols From the Kernel (vmlinux + modules)
+-------------------------------------------
+
+	During a kernel build, a file named Module.symvers will be
+	generated. Module.symvers contains all exported symbols from
+	the kernel and compiled modules. For each symbol, the
+	corresponding CRC value is also stored.
+
+	The syntax of the Module.symvers file is::
+
+		<CRC>       <Symbol>         <Module>                         <Export Type>     <Namespace>
+
+		0xe1cc2a05  usb_stor_suspend drivers/usb/storage/usb-storage  EXPORT_SYMBOL_GPL USB_STORAGE
+
+	The fields are separated by tabs and values may be empty (e.g.
+	if no namespace is defined for an exported symbol).
+
+	For a kernel build without CONFIG_MODVERSIONS enabled, the CRC
+	would read 0x00000000.
+
+	Module.symvers serves two purposes:
+
+	1) It lists all exported symbols from vmlinux and all modules.
+	2) It lists the CRC if CONFIG_MODVERSIONS is enabled.
+
+Version Information Formats
+---------------------------
+
+	Exported symbols have information stored in the __ksymtab and
+	__kflagstab sections. Symbol names and namespaces are stored in
+	__ksymtab_strings section, using a format similar to the string
+	table used for ELF. If CONFIG_MODVERSIONS is enabled, the CRCs
+	corresponding to exported symbols will be added to the
+	__kcrctab section.
+
+	If CONFIG_BASIC_MODVERSIONS is enabled (default with
+	CONFIG_MODVERSIONS), imported symbols will have their symbol name and
+	CRC stored in the __versions section of the importing module. This
+	mode only supports symbols of length up to 64 bytes.
+
+	If CONFIG_EXTENDED_MODVERSIONS is enabled (required to enable both
+	CONFIG_MODVERSIONS and CONFIG_RUST at the same time), imported symbols
+	will have their symbol name recorded in the __version_ext_names
+	section as a series of concatenated, null-terminated strings. CRCs for
+	these symbols will be recorded in the __version_ext_crcs section.
+
+Symbols and External Modules
+----------------------------
+
+	When building an external module, the build system needs access
+	to the symbols from the kernel to check if all external symbols
+	are defined. This is done in the MODPOST step. modpost obtains
+	the symbols by reading Module.symvers from the kernel source
+	tree. During the MODPOST step, a new Module.symvers file will be
+	written containing all exported symbols from that external module.
+
+Symbols From Another External Module
+------------------------------------
+
+	Sometimes, an external module uses exported symbols from
+	another external module. Kbuild needs to have full knowledge of
+	all symbols to avoid spitting out warnings about undefined
+	symbols. Two solutions exist for this situation.
+
+	NOTE: The method with a top-level kbuild file is recommended
+	but may be impractical in certain situations.
+
+	Use a top-level kbuild file
+		If you have two modules, foo.ko and bar.ko, where
+		foo.ko needs symbols from bar.ko, you can use a
+		common top-level kbuild file so both modules are
+		compiled in the same build. Consider the following
+		directory layout::
+
+			./foo/ <= contains foo.ko
+			./bar/ <= contains bar.ko
+
+		The top-level kbuild file would then look like::
+
+			#./Kbuild (or ./Makefile):
+				obj-m := foo/ bar/
+
+		And executing::
+
+			$ make -C $KDIR M=$PWD
+
+		will then do the expected and compile both modules with
+		full knowledge of symbols from either module.
+
+	Use "make" variable KBUILD_EXTRA_SYMBOLS
+		If it is impractical to add a top-level kbuild file,
+		you can assign a space separated list
+		of files to KBUILD_EXTRA_SYMBOLS in your build file.
+		These files will be loaded by modpost during the
+		initialization of its symbol tables.
+
+
+Tips & Tricks
+=============
+
+Testing for CONFIG_FOO_BAR
+--------------------------
+
+	Modules often need to check for certain `CONFIG_` options to
+	decide if a specific feature is included in the module. In
+	kbuild this is done by referencing the `CONFIG_` variable
+	directly::
+
+		#fs/ext2/Makefile
+		obj-$(CONFIG_EXT2_FS) += ext2.o
+
+		ext2-y := balloc.o bitmap.o dir.o
+		ext2-$(CONFIG_EXT2_FS_XATTR) += xattr.o
diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
new file mode 100644
index 000000000..bc1eb8221
--- /dev/null
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -0,0 +1,143 @@
+===================
+Reproducible builds
+===================
+
+It is generally desirable that building the same source code with
+the same set of tools is reproducible, i.e. the output is always
+exactly the same.  This makes it possible to verify that the build
+infrastructure for a binary distribution or embedded system has not
+been subverted.  This can also make it easier to verify that a source
+or tool change does not make any difference to the resulting binaries.
+
+The `Reproducible Builds project`_ has more information about this
+general topic.  This document covers the various reasons why building
+the kernel may be unreproducible, and how to avoid them.
+
+Timestamps
+----------
+
+The kernel embeds timestamps in three places:
+
+* The version string exposed by ``uname()`` and included in
+  ``/proc/version``
+
+* File timestamps in the embedded initramfs
+
+* If enabled via ``CONFIG_IKHEADERS``, file timestamps of kernel
+  headers embedded in the kernel or respective module,
+  exposed via ``/sys/kernel/kheaders.tar.xz``
+
+By default the timestamp is the current time and in the case of
+``kheaders`` the various files' modification times. This must
+be overridden using the `KBUILD_BUILD_TIMESTAMP`_ variable.
+If you are building from a git commit, you could use its commit date.
+
+The kernel does *not* use the ``__DATE__`` and ``__TIME__`` macros,
+and enables warnings if they are used.  If you incorporate external
+code that does use these, you must override the timestamp they
+correspond to by setting the `SOURCE_DATE_EPOCH`_ environment
+variable.
+
+User, host
+----------
+
+The kernel embeds the building user and host names in
+``/proc/version``.  These must be overridden using the
+`KBUILD_BUILD_USER and KBUILD_BUILD_HOST`_ variables.  If you are
+building from a git commit, you could use its committer address.
+
+Absolute filenames
+------------------
+
+When the kernel is built out-of-tree, debug information may include
+absolute filenames for the source files and build directory.  These must
+be overridden by including a ``-fdebug-prefix-map`` option for each in
+the `KCFLAGS`_ and `KAFLAGS`_ variables to cover both ``.c`` and ``.S``
+files.
+
+Depending on the compiler used, the ``__FILE__`` macro may also expand
+to an absolute filename in an out-of-tree build.  Kbuild automatically
+uses the ``-fmacro-prefix-map`` option to prevent this, if it is
+supported.
+
+The Reproducible Builds web site has more information about these
+`prefix-map options`_.
+
+Some CONFIG options such as `CONFIG_DEBUG_EFI` embed absolute paths in
+object files. Such options should be disabled.
+
+Generated files in source packages
+----------------------------------
+
+The build processes for some programs under the ``tools/``
+subdirectory do not completely support out-of-tree builds.  This may
+cause a later source package build using e.g. ``make rpm-pkg`` to
+include generated files.  You should ensure the source tree is
+pristine by running ``make mrproper`` or ``git clean -d -f -x`` before
+building a source package.
+
+Module signing
+--------------
+
+If you enable ``CONFIG_MODULE_SIG_ALL``, the default behaviour is to
+generate a different temporary key for each build, resulting in the
+modules being unreproducible.  However, including a signing key with
+your source would presumably defeat the purpose of signing modules.
+
+One approach to this is to divide up the build process so that the
+unreproducible parts can be treated as sources:
+
+1. Generate a persistent signing key.  Add the certificate for the key
+   to the kernel source.
+
+2. Set the ``CONFIG_SYSTEM_TRUSTED_KEYS`` symbol to include the
+   signing key's certificate, set ``CONFIG_MODULE_SIG_KEY`` to an
+   empty string, and disable ``CONFIG_MODULE_SIG_ALL``.
+   Build the kernel and modules.
+
+3. Create detached signatures for the modules, and publish them as
+   sources.
+
+4. Perform a second build that attaches the module signatures.  It
+   can either rebuild the modules or use the output of step 2.
+
+Structure randomisation
+-----------------------
+
+If you enable ``CONFIG_RANDSTRUCT``, you will need to pre-generate
+the random seed in ``scripts/basic/randstruct.seed`` so the same
+value is used by each build. See ``scripts/gen-randstruct-seed.sh``
+for details.
+
+Debug info conflicts
+--------------------
+
+This is not a problem of unreproducibility, but of generated files
+being *too* reproducible.
+
+Once you set all the necessary variables for a reproducible build, a
+vDSO's debug information may be identical even for different kernel
+versions.  This can result in file conflicts between debug information
+packages for the different kernel versions.
+
+To avoid this, you can make the vDSO different for different
+kernel versions by including an arbitrary string of "salt" in it.
+This is specified by the Kconfig symbol ``CONFIG_BUILD_SALT``.
+
+Git
+---
+
+Uncommitted changes or different commit ids in git can also lead
+to different compilation results. For example, after executing
+``git reset HEAD^``, even if the code is the same, the
+``include/config/kernel.release`` generated during compilation
+will be different, which will eventually lead to binary differences.
+See ``scripts/setlocalversion`` for details.
+
+.. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp
+.. _KBUILD_BUILD_USER and KBUILD_BUILD_HOST: kbuild.html#kbuild-build-user-kbuild-build-host
+.. _KCFLAGS: kbuild.html#kcflags
+.. _KAFLAGS: kbuild.html#kaflags
+.. _prefix-map options: https://reproducible-builds.org/docs/build-path/
+.. _Reproducible Builds project: https://reproducible-builds.org/
+.. _SOURCE_DATE_EPOCH: https://reproducible-builds.org/docs/source-date-epoch/