kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 170 insertions, 0 deletions

diff --git a/Documentation/driver-api/regulator.rst b/Documentation/driver-api/regulator.rst
new file mode 100644
index 000000000..b43c78eb2
--- /dev/null
+++ b/Documentation/driver-api/regulator.rst
@@ -0,0 +1,170 @@
+.. Copyright 2007-2008 Wolfson Microelectronics
+
+..   This documentation is free software; you can redistribute
+..   it and/or modify it under the terms of the GNU General Public
+..   License version 2 as published by the Free Software Foundation.
+
+=================================
+Voltage and current regulator API
+=================================
+
+:Author: Liam Girdwood
+:Author: Mark Brown
+
+Introduction
+============
+
+This framework is designed to provide a standard kernel interface to
+control voltage and current regulators.
+
+The intention is to allow systems to dynamically control regulator power
+output in order to save power and prolong battery life. This applies to
+both voltage regulators (where voltage output is controllable) and
+current sinks (where current limit is controllable).
+
+Note that additional (and currently more complete) documentation is
+available in the Linux kernel source under
+``Documentation/power/regulator``.
+
+Glossary
+--------
+
+The regulator API uses a number of terms which may not be familiar:
+
+Regulator
+
+    Electronic device that supplies power to other devices. Most regulators
+    can enable and disable their output and some can also control their
+    output voltage or current.
+
+Consumer
+
+    Electronic device which consumes power provided by a regulator. These
+    may either be static, requiring only a fixed supply, or dynamic,
+    requiring active management of the regulator at runtime.
+
+Power Domain
+
+    The electronic circuit supplied by a given regulator, including the
+    regulator and all consumer devices. The configuration of the regulator
+    is shared between all the components in the circuit.
+
+Power Management Integrated Circuit (PMIC)
+
+    An IC which contains numerous regulators and often also other
+    subsystems. In an embedded system the primary PMIC is often equivalent
+    to a combination of the PSU and southbridge in a desktop system.
+
+Consumer driver interface
+=========================
+
+This offers a similar API to the kernel clock framework. Consumer
+drivers use `get <#API-regulator-get>`__ and
+`put <#API-regulator-put>`__ operations to acquire and release
+regulators. Functions are provided to `enable <#API-regulator-enable>`__
+and `disable <#API-regulator-disable>`__ the regulator and to get and
+set the runtime parameters of the regulator.
+
+When requesting regulators consumers use symbolic names for their
+supplies, such as "Vcc", which are mapped into actual regulator devices
+by the machine interface.
+
+A stub version of this API is provided when the regulator framework is
+not in use in order to minimise the need to use ifdefs.
+
+Enabling and disabling
+----------------------
+
+The regulator API provides reference counted enabling and disabling of
+regulators. Consumer devices use the :c:func:`regulator_enable()` and
+:c:func:`regulator_disable()` functions to enable and disable
+regulators. Calls to the two functions must be balanced.
+
+Note that since multiple consumers may be using a regulator and machine
+constraints may not allow the regulator to be disabled there is no
+guarantee that calling :c:func:`regulator_disable()` will actually
+cause the supply provided by the regulator to be disabled. Consumer
+drivers should assume that the regulator may be enabled at all times.
+
+Configuration
+-------------
+
+Some consumer devices may need to be able to dynamically configure their
+supplies. For example, MMC drivers may need to select the correct
+operating voltage for their cards. This may be done while the regulator
+is enabled or disabled.
+
+The :c:func:`regulator_set_voltage()` and
+:c:func:`regulator_set_current_limit()` functions provide the primary
+interface for this. Both take ranges of voltages and currents, supporting
+drivers that do not require a specific value (eg, CPU frequency scaling
+normally permits the CPU to use a wider range of supply voltages at lower
+frequencies but does not require that the supply voltage be lowered). Where
+an exact value is required both minimum and maximum values should be
+identical.
+
+Callbacks
+---------
+
+Callbacks may also be registered for events such as regulation failures.
+
+Regulator driver interface
+==========================
+
+Drivers for regulator chips register the regulators with the regulator
+core, providing operations structures to the core. A notifier interface
+allows error conditions to be reported to the core.
+
+Registration should be triggered by explicit setup done by the platform,
+supplying a struct regulator_init_data for the regulator
+containing constraint and supply information.
+
+Machine interface
+=================
+
+This interface provides a way to define how regulators are connected to
+consumers on a given system and what the valid operating parameters are
+for the system.
+
+Supplies
+--------
+
+Regulator supplies are specified using struct
+:c:type:`regulator_consumer_supply`. This is done at driver registration
+time as part of the machine constraints.
+
+Constraints
+-----------
+
+As well as defining the connections the machine interface also provides
+constraints defining the operations that clients are allowed to perform
+and the parameters that may be set. This is required since generally
+regulator devices will offer more flexibility than it is safe to use on
+a given system, for example supporting higher supply voltages than the
+consumers are rated for.
+
+This is done at driver registration time` by providing a
+struct regulation_constraints.
+
+The constraints may also specify an initial configuration for the
+regulator in the constraints, which is particularly useful for use with
+static consumers.
+
+API reference
+=============
+
+Due to limitations of the kernel documentation framework and the
+existing layout of the source code the entire regulator API is
+documented here.
+
+.. kernel-doc:: include/linux/regulator/consumer.h
+   :internal:
+
+.. kernel-doc:: include/linux/regulator/machine.h
+   :internal:
+
+.. kernel-doc:: include/linux/regulator/driver.h
+   :internal:
+
+.. kernel-doc:: drivers/regulator/core.c
+   :export: