sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 515 insertions, 0 deletions

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
new file mode 100644
index 000000000..0a4fdd8bd
--- /dev/null
+++ b/scripts/Makefile.lib
@@ -0,0 +1,515 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Finds the multi-part object the current object will be linked into.
+# If the object belongs to two or more multi-part objects, list them all.
+modname-multi = $(sort $(foreach m,$(multi-obj-ym),\
+		$(if $(filter $*.o, $(call suffix-search, $m, .o, -objs -y -m)),$(m:.o=))))
+
+__modname = $(or $(modname-multi),$(basetarget))
+
+modname = $(subst $(space),:,$(__modname))
+modfile = $(addprefix $(obj)/,$(__modname))
+
+# target with $(obj)/ and its suffix stripped
+target-stem = $(basename $(patsubst $(obj)/%,%,$@))
+
+# These flags are needed for modversions and compiling, so we define them here
+# $(modname_flags) defines KBUILD_MODNAME as the name of the module it will
+# end up in (or would, if it gets compiled in)
+name-fix-token = $(subst $(comma),_,$(subst -,_,$1))
+name-fix = $(call stringify,$(call name-fix-token,$1))
+basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget))
+modname_flags  = -DKBUILD_MODNAME=$(call name-fix,$(modname)) \
+		 -D__KBUILD_MODNAME=$(call name-fix-token,$(modname))
+modfile_flags  = -DKBUILD_MODFILE=$(call stringify,$(modfile))
+
+_c_flags       = $(filter-out $(CFLAGS_REMOVE_$(target-stem).o), \
+                     $(filter-out $(ccflags-remove-y), \
+                         $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) $(ccflags-y)) \
+                     $(CFLAGS_$(target-stem).o))
+_rust_flags    = $(filter-out $(RUSTFLAGS_REMOVE_$(target-stem).o), \
+                     $(filter-out $(rustflags-remove-y), \
+                         $(KBUILD_RUSTFLAGS) $(rustflags-y)) \
+                     $(RUSTFLAGS_$(target-stem).o))
+_a_flags       = $(filter-out $(AFLAGS_REMOVE_$(target-stem).o), \
+                     $(filter-out $(asflags-remove-y), \
+                         $(KBUILD_CPPFLAGS) $(KBUILD_AFLAGS) $(asflags-y)) \
+                     $(AFLAGS_$(target-stem).o))
+_cpp_flags     = $(KBUILD_CPPFLAGS) $(cppflags-y) $(CPPFLAGS_$(target-stem).lds)
+
+#
+# Enable gcov profiling flags for a file, directory or for all files depending
+# on variables GCOV_PROFILE_obj.o, GCOV_PROFILE and CONFIG_GCOV_PROFILE_ALL
+# (in this order)
+#
+ifeq ($(CONFIG_GCOV_KERNEL),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(GCOV_PROFILE_$(target-stem).o)$(GCOV_PROFILE)$(if $(is-kernel-object),$(CONFIG_GCOV_PROFILE_ALL))), \
+		$(CFLAGS_GCOV))
+endif
+
+#
+# Enable address sanitizer flags for kernel except some files or directories
+# we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)
+#
+ifeq ($(CONFIG_KASAN),y)
+ifneq ($(CONFIG_KASAN_HW_TAGS),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(KASAN_SANITIZE_$(target-stem).o)$(KASAN_SANITIZE)$(is-kernel-object)), \
+		$(CFLAGS_KASAN), $(CFLAGS_KASAN_NOSANITIZE))
+_rust_flags += $(if $(patsubst n%,, \
+		$(KASAN_SANITIZE_$(target-stem).o)$(KASAN_SANITIZE)$(is-kernel-object)), \
+		$(RUSTFLAGS_KASAN))
+endif
+endif
+
+ifeq ($(CONFIG_KMSAN),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(KMSAN_SANITIZE_$(target-stem).o)$(KMSAN_SANITIZE)$(is-kernel-object)), \
+		$(CFLAGS_KMSAN))
+_c_flags += $(if $(patsubst n%,, \
+		$(KMSAN_ENABLE_CHECKS_$(target-stem).o)$(KMSAN_ENABLE_CHECKS)$(is-kernel-object)), \
+		, -mllvm -msan-disable-checks=1)
+endif
+
+ifeq ($(CONFIG_UBSAN),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(UBSAN_SANITIZE_$(target-stem).o)$(UBSAN_SANITIZE)$(is-kernel-object)), \
+		$(CFLAGS_UBSAN))
+_c_flags += $(if $(patsubst n%,, \
+		$(UBSAN_INTEGER_WRAP_$(target-stem).o)$(UBSAN_SANITIZE_$(target-stem).o)$(UBSAN_INTEGER_WRAP)$(UBSAN_SANITIZE)$(is-kernel-object)), \
+		$(CFLAGS_UBSAN_INTEGER_WRAP))
+endif
+
+ifeq ($(CONFIG_KCOV),y)
+_c_flags += $(if $(patsubst n%,, \
+	$(KCOV_INSTRUMENT_$(target-stem).o)$(KCOV_INSTRUMENT)$(if $(is-kernel-object),$(CONFIG_KCOV_INSTRUMENT_ALL))), \
+	$(CFLAGS_KCOV))
+_rust_flags += $(if $(patsubst n%,, \
+	$(KCOV_INSTRUMENT_$(target-stem).o)$(KCOV_INSTRUMENT)$(if $(is-kernel-object),$(CONFIG_KCOV_INSTRUMENT_ALL))), \
+	$(RUSTFLAGS_KCOV))
+endif
+
+#
+# Enable KCSAN flags except some files or directories we don't want to check
+# (depends on variables KCSAN_SANITIZE_obj.o, KCSAN_SANITIZE)
+#
+ifeq ($(CONFIG_KCSAN),y)
+_c_flags += $(if $(patsubst n%,, \
+	$(KCSAN_SANITIZE_$(target-stem).o)$(KCSAN_SANITIZE)$(is-kernel-object)), \
+	$(CFLAGS_KCSAN))
+# Some uninstrumented files provide implied barriers required to avoid false
+# positives: set KCSAN_INSTRUMENT_BARRIERS for barrier instrumentation only.
+_c_flags += $(if $(patsubst n%,, \
+	$(KCSAN_INSTRUMENT_BARRIERS_$(target-stem).o)$(KCSAN_INSTRUMENT_BARRIERS)n), \
+	-D__KCSAN_INSTRUMENT_BARRIERS__)
+endif
+
+#
+# Enable context analysis flags only where explicitly opted in.
+# (depends on variables CONTEXT_ANALYSIS_obj.o, CONTEXT_ANALYSIS)
+#
+ifeq ($(CONFIG_WARN_CONTEXT_ANALYSIS),y)
+_c_flags += $(if $(patsubst n%,, \
+		$(CONTEXT_ANALYSIS_$(target-stem).o)$(CONTEXT_ANALYSIS)$(if $(is-kernel-object),$(CONFIG_WARN_CONTEXT_ANALYSIS_ALL))), \
+		$(CFLAGS_CONTEXT_ANALYSIS))
+endif
+
+#
+# Enable AutoFDO build flags except some files or directories we don't want to
+# enable (depends on variables AUTOFDO_PROFILE_obj.o and AUTOFDO_PROFILE).
+#
+ifeq ($(CONFIG_AUTOFDO_CLANG),y)
+_c_flags += $(if $(patsubst n%,, \
+	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \
+	$(CFLAGS_AUTOFDO_CLANG))
+_rust_flags += $(if $(patsubst n%,, \
+	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(is-kernel-object)), \
+	$(RUSTFLAGS_AUTOFDO_CLANG))
+endif
+
+#
+# Enable Propeller build flags except some files or directories we don't want to
+# enable (depends on variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE).
+#
+ifdef CONFIG_PROPELLER_CLANG
+_c_flags += $(if $(patsubst n%,, \
+	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(PROPELLER_PROFILE))$(is-kernel-object), \
+	$(CFLAGS_PROPELLER_CLANG))
+endif
+
+# $(src) for including checkin headers from generated source files
+# $(obj) for including generated headers from checkin source files
+ifdef building_out_of_srctree
+_c_flags   += $(addprefix -I, $(src) $(obj))
+_a_flags   += $(addprefix -I, $(src) $(obj))
+_cpp_flags += $(addprefix -I, $(src) $(obj))
+endif
+
+# If $(is-kernel-object) is 'y', this object will be linked to vmlinux or modules
+is-kernel-object = $(or $(part-of-builtin),$(part-of-module))
+
+part-of-builtin = $(if $(filter $(basename $@).o, $(real-obj-y) $(lib-y)),y)
+part-of-module = $(if $(filter $(basename $@).o, $(real-obj-m)),y)
+quiet_modtag = $(if $(part-of-module),[M],   )
+
+modkern_cflags =                                          \
+	$(if $(part-of-module),                           \
+		$(KBUILD_CFLAGS_MODULE) $(CFLAGS_MODULE), \
+		$(KBUILD_CFLAGS_KERNEL) $(CFLAGS_KERNEL) $(modfile_flags))
+
+modkern_rustflags =                                              \
+	$(if $(part-of-module),                                   \
+		$(KBUILD_RUSTFLAGS_MODULE) $(RUSTFLAGS_MODULE), \
+		$(KBUILD_RUSTFLAGS_KERNEL) $(RUSTFLAGS_KERNEL))
+
+modkern_aflags = $(if $(part-of-module),				\
+			$(KBUILD_AFLAGS_MODULE) $(AFLAGS_MODULE),	\
+			$(KBUILD_AFLAGS_KERNEL) $(AFLAGS_KERNEL) $(modfile_flags))
+
+c_flags        = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
+		 -include $(srctree)/include/linux/compiler_types.h       \
+		 $(_c_flags) $(modkern_cflags)                           \
+		 $(basename_flags) $(modname_flags)
+
+rust_flags     = $(_rust_flags) $(modkern_rustflags) @$(objtree)/include/generated/rustc_cfg
+
+a_flags        = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
+		 $(_a_flags) $(modkern_aflags) $(modname_flags)
+
+cpp_flags      = -Wp,-MMD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
+		 $(_cpp_flags)
+
+ld_flags       = $(KBUILD_LDFLAGS) $(ldflags-y) $(LDFLAGS_$(@F))
+
+ifdef CONFIG_OBJTOOL
+
+objtool := $(objtree)/tools/objtool/objtool
+
+objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)		+= --hacks=jump_label
+objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)		+= --hacks=noinstr
+objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)	+= --hacks=skylake
+objtool-args-$(CONFIG_X86_KERNEL_IBT)			+= --ibt
+objtool-args-$(CONFIG_CALL_PADDING)			+= --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
+ifdef CONFIG_CALL_PADDING
+objtool-args-$(CONFIG_CFI)				+= --cfi
+objtool-args-$(CONFIG_FINEIBT)				+= --fineibt
+endif
+objtool-args-$(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL)	+= --mcount
+ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
+objtool-args-$(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT)		+= --mnop
+endif
+objtool-args-$(CONFIG_UNWINDER_ORC)			+= --orc
+objtool-args-$(CONFIG_MITIGATION_RETPOLINE)		+= --retpoline
+objtool-args-$(CONFIG_MITIGATION_RETHUNK)		+= --rethunk
+objtool-args-$(CONFIG_MITIGATION_SLS)			+= --sls
+objtool-args-$(CONFIG_STACK_VALIDATION)			+= --stackval
+objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE)		+= --static-call
+objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION)		+= --uaccess
+objtool-args-$(or $(CONFIG_GCOV_KERNEL),$(CONFIG_KCOV))	+= --no-unreachable
+objtool-args-$(CONFIG_OBJTOOL_WERROR)			+= --werror
+
+objtool-args = $(objtool-args-y)					\
+	$(if $(delay-objtool), --link)					\
+	$(if $(part-of-module), --module)
+
+delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT),$(CONFIG_KLP_BUILD))
+
+cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool-args) $@)
+cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
+
+objtool-enabled := y
+
+endif # CONFIG_OBJTOOL
+
+# Useful for describing the dependency of composite objects
+# Usage:
+#   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
+define multi_depend
+$(foreach m, $1, \
+	$(eval $m: \
+	$(addprefix $(obj)/, $(call suffix-search, $(patsubst $(obj)/%,%,$m), $2, $3))))
+endef
+
+# Remove ".." and "." from a path, without using "realpath"
+# Usage:
+#   $(call normalize_path,path/to/../file)
+define normalize_path
+$(strip $(eval elements :=) \
+$(foreach elem,$(subst /, ,$1), \
+	$(if $(filter-out .,$(elem)), \
+	     $(if $(filter ..,$(elem)), \
+		  $(eval elements := $(wordlist 2,$(words $(elements)),x $(elements))), \
+		  $(eval elements := $(elements) $(elem))))) \
+$(subst $(space),/,$(elements)))
+endef
+
+# Build commands
+# ===========================================================================
+# These are shared by some Makefile.* files.
+
+ifdef CONFIG_LTO_CLANG
+# Run $(LD) here to convert LLVM IR to ELF in the following cases:
+#  - when this object needs objtool processing, as objtool cannot process LLVM IR
+#  - when this is a single-object module, as modpost cannot process LLVM IR
+cmd_ld_single = $(if $(objtool-enabled)$(is-single-obj-m), ; $(LD) $(ld_flags) -r -o $(tmp-target) $@; mv $(tmp-target) $@)
+endif
+
+ifdef CONFIG_LTO_CLANG_THIN_DIST
+# Save the _c_flags, sliently.
+quiet_cmd_save_c_flags =
+      saved_c_flags = $(_c_flags) $(modkern_cflags)
+      cmd_save_c_flags = printf '\n%s\n' 'saved_c_flags_$@ := $(call escsq,$(saved_c_flags))' >> $(dot-target).cmd
+endif
+
+quiet_cmd_cc_o_c = CC $(quiet_modtag)  $@
+      cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $< \
+		$(cmd_ld_single) \
+		$(cmd_objtool)
+
+define rule_cc_o_c
+	$(call cmd_and_fixdep,cc_o_c)
+	$(call cmd,save_c_flags)
+	$(call cmd,checksrc)
+	$(call cmd,checkdoc)
+	$(call cmd,gen_objtooldep)
+	$(call cmd,gen_symversions_c)
+	$(call cmd,record_mcount)
+	$(call cmd,warn_shared_object)
+endef
+
+quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
+      cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $< $(cmd_objtool)
+
+define rule_as_o_S
+	$(call cmd_and_fixdep,as_o_S)
+	$(call cmd,gen_objtooldep)
+	$(call cmd,gen_symversions_S)
+	$(call cmd,warn_shared_object)
+endef
+
+# Copy a file
+# ===========================================================================
+# 'cp' preserves permissions. If you use it to copy a file in read-only srctree,
+# the copy would be read-only as well, leading to an error when executing the
+# rule next time. Use 'cat' instead in order to generate a writable file.
+quiet_cmd_copy = COPY    $@
+      cmd_copy = cat $< > $@
+
+$(obj)/%: $(src)/%_shipped
+	$(call cmd,copy)
+
+# Touch a file
+# ===========================================================================
+quiet_cmd_touch = TOUCH   $(call normalize_path,$@)
+      cmd_touch = touch $@
+
+# Commands useful for building a boot image
+# ===========================================================================
+#
+#	Use as following:
+#
+#	target: source(s) FORCE
+#		$(if_changed,ld/objcopy/gzip)
+#
+#	and add target to 'targets' so that we know we have to
+#	read in the saved command line
+
+# Linking
+# ---------------------------------------------------------------------------
+
+quiet_cmd_ld = LD      $@
+      cmd_ld = $(LD) $(ld_flags) $(real-prereqs) -o $@
+
+# Archive
+# ---------------------------------------------------------------------------
+
+quiet_cmd_ar = AR      $@
+      cmd_ar = rm -f $@; $(AR) cDPrsT $@ $(real-prereqs)
+
+# Objcopy
+# ---------------------------------------------------------------------------
+
+quiet_cmd_objcopy = OBJCOPY $@
+cmd_objcopy = $(OBJCOPY) $(OBJCOPYFLAGS) $(OBJCOPYFLAGS_$(@F)) $< $@
+
+# Gzip
+# ---------------------------------------------------------------------------
+
+quiet_cmd_gzip = GZIP    $@
+      cmd_gzip = cat $(real-prereqs) | $(KGZIP) -n -f -9 > $@
+
+# Bzip2
+# ---------------------------------------------------------------------------
+
+# Bzip2 and LZMA do not include size in file... so we have to fake that;
+# append the size as a 32-bit littleendian number as gzip does.
+size_append = printf $(shell						\
+dec_size=0;								\
+for F in $(real-prereqs); do					\
+	fsize=$$($(CONFIG_SHELL) $(srctree)/scripts/file-size.sh $$F);	\
+	dec_size=$$(expr $$dec_size + $$fsize);				\
+done;									\
+printf "%08x\n" $$dec_size |						\
+	sed 's/\(..\)/\1 /g' | {					\
+		read ch0 ch1 ch2 ch3;					\
+		for ch in $$ch3 $$ch2 $$ch1 $$ch0; do			\
+			printf '%s%03o' '\\' $$((0x$$ch)); 		\
+		done;							\
+	}								\
+)
+
+quiet_cmd_file_size = GEN     $@
+      cmd_file_size = $(size_append) > $@
+
+quiet_cmd_bzip2 = BZIP2   $@
+      cmd_bzip2 = cat $(real-prereqs) | $(KBZIP2) -9 > $@
+
+quiet_cmd_bzip2_with_size = BZIP2   $@
+      cmd_bzip2_with_size = { cat $(real-prereqs) | $(KBZIP2) -9; $(size_append); } > $@
+
+# Lzma
+# ---------------------------------------------------------------------------
+
+quiet_cmd_lzma = LZMA    $@
+      cmd_lzma = cat $(real-prereqs) | $(LZMA) -9 > $@
+
+quiet_cmd_lzma_with_size = LZMA    $@
+      cmd_lzma_with_size = { cat $(real-prereqs) | $(LZMA) -9; $(size_append); } > $@
+
+quiet_cmd_lzo = LZO     $@
+      cmd_lzo = cat $(real-prereqs) | $(KLZOP) -9 > $@
+
+quiet_cmd_lzo_with_size = LZO     $@
+      cmd_lzo_with_size = { cat $(real-prereqs) | $(KLZOP) -9; $(size_append); } > $@
+
+quiet_cmd_lz4 = LZ4     $@
+      cmd_lz4 = cat $(real-prereqs) | $(LZ4) -l -9 - - > $@
+
+quiet_cmd_lz4_with_size = LZ4     $@
+      cmd_lz4_with_size = { cat $(real-prereqs) | $(LZ4) -l -9 - -; \
+                  $(size_append); } > $@
+
+# U-Boot mkimage
+# ---------------------------------------------------------------------------
+
+MKIMAGE := $(srctree)/scripts/mkuboot.sh
+
+# SRCARCH just happens to match slightly more than ARCH (on sparc), so reduces
+# the number of overrides in arch makefiles
+UIMAGE_ARCH ?= $(SRCARCH)
+UIMAGE_COMPRESSION ?= $(or $(2),none)
+UIMAGE_OPTS-y ?=
+UIMAGE_TYPE ?= kernel
+UIMAGE_LOADADDR ?= arch_must_set_this
+UIMAGE_ENTRYADDR ?= $(UIMAGE_LOADADDR)
+UIMAGE_NAME ?= Linux-$(KERNELRELEASE)
+
+quiet_cmd_uimage = UIMAGE  $@
+      cmd_uimage = $(BASH) $(MKIMAGE) -A $(UIMAGE_ARCH) -O linux \
+			-C $(UIMAGE_COMPRESSION) $(UIMAGE_OPTS-y) \
+			-T $(UIMAGE_TYPE) \
+			-a $(UIMAGE_LOADADDR) -e $(UIMAGE_ENTRYADDR) \
+			-n '$(UIMAGE_NAME)' -d $< $@
+
+# Flat Image Tree (FIT)
+# This allows for packaging of a kernel and all devicetrees files, using
+# compression.
+# ---------------------------------------------------------------------------
+
+MAKE_FIT := $(srctree)/scripts/make_fit.py
+
+# Use this to override the compression algorithm
+FIT_COMPRESSION ?= gzip
+
+quiet_cmd_fit = FIT     $@
+      cmd_fit = $(MAKE_FIT) -o $@ --arch $(UIMAGE_ARCH) --os linux \
+		--name '$(UIMAGE_NAME)' $(FIT_EXTRA_ARGS) \
+		$(if $(findstring 1,$(KBUILD_VERBOSE)),-v) \
+		$(if $(FIT_DECOMPOSE_DTBS),--decompose-dtbs) \
+		--compress $(FIT_COMPRESSION) -k $< @$(word 2,$^)
+
+# XZ
+# ---------------------------------------------------------------------------
+# Use xzkern or xzkern_with_size to compress the kernel image and xzmisc to
+# compress other things.
+#
+# xzkern uses a big LZMA2 dictionary since it doesn't increase memory usage
+# of the kernel decompressor. A BCJ filter is used if it is available for
+# the target architecture.
+#
+# xzkern_with_size also appends uncompressed size of the data using
+# size_append. The .xz format has the size information available at the end
+# of the file too, but it's in more complex format and it's good to avoid
+# changing the part of the boot code that reads the uncompressed size.
+# Note that the bytes added by size_append will make the xz tool think that
+# the file is corrupt. This is expected.
+#
+# xzmisc doesn't use size_append, so it can be used to create normal .xz
+# files. xzmisc uses smaller LZMA2 dictionary than xzkern, because a very
+# big dictionary would increase the memory usage too much in the multi-call
+# decompression mode. A BCJ filter isn't used either.
+quiet_cmd_xzkern = XZKERN  $@
+      cmd_xzkern = cat $(real-prereqs) | sh $(srctree)/scripts/xz_wrap.sh > $@
+
+quiet_cmd_xzkern_with_size = XZKERN  $@
+      cmd_xzkern_with_size = { cat $(real-prereqs) | sh $(srctree)/scripts/xz_wrap.sh; \
+                     $(size_append); } > $@
+
+quiet_cmd_xzmisc = XZMISC  $@
+      cmd_xzmisc = cat $(real-prereqs) | $(XZ) --check=crc32 --lzma2=dict=1MiB > $@
+
+# ZSTD
+# ---------------------------------------------------------------------------
+# Appends the uncompressed size of the data using size_append. The .zst
+# format has the size information available at the beginning of the file too,
+# but it's in a more complex format and it's good to avoid changing the part
+# of the boot code that reads the uncompressed size.
+#
+# Note that the bytes added by size_append will make the zstd tool think that
+# the file is corrupt. This is expected.
+#
+# zstd uses a maximum window size of 8 MB. zstd22 uses a maximum window size of
+# 128 MB. zstd22 is used for kernel compression because it is decompressed in a
+# single pass, so zstd doesn't need to allocate a window buffer. When streaming
+# decompression is used, like initramfs decompression, zstd22 should likely not
+# be used because it would require zstd to allocate a 128 MB buffer.
+
+quiet_cmd_zstd = ZSTD    $@
+      cmd_zstd = cat $(real-prereqs) | $(ZSTD) -19 > $@
+
+quiet_cmd_zstd22 = ZSTD22  $@
+      cmd_zstd22 = cat $(real-prereqs) | $(ZSTD) -22 --ultra > $@
+
+quiet_cmd_zstd22_with_size = ZSTD22  $@
+      cmd_zstd22_with_size = { cat $(real-prereqs) | $(ZSTD) -22 --ultra; $(size_append); } > $@
+
+# ASM offsets
+# ---------------------------------------------------------------------------
+
+# Default sed regexp - multiline due to syntax constraints
+#
+# Use [:space:] because LLVM's integrated assembler inserts <tab> around
+# the .ascii directive whereas GCC keeps the <space> as-is.
+define sed-offsets
+	's:^[[:space:]]*\.ascii[[:space:]]*"\(.*\)".*:\1:; \
+	/^->/{s:->#\(.*\):/* \1 */:; \
+	s:^->\([^ ]*\) [\$$#]*\([^ ]*\) \(.*\):#define \1 \2 /* \3 */:; \
+	s:->::; p;}'
+endef
+
+# Use filechk to avoid rebuilds when a header changes, but the resulting file
+# does not
+define filechk_offsets
+	 echo "#ifndef $2"; \
+	 echo "#define $2"; \
+	 echo "/*"; \
+	 echo " * DO NOT MODIFY."; \
+	 echo " *"; \
+	 echo " * This file was generated by Kbuild"; \
+	 echo " */"; \
+	 echo ""; \
+	 sed -ne $(sed-offsets) < $<; \
+	 echo ""; \
+	 echo "#endif"
+endef