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, 89 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-led-flash b/Documentation/ABI/testing/sysfs-class-led-flash
new file mode 100644
index 000000000..11e5677c3
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-led-flash
@@ -0,0 +1,89 @@
+What:		/sys/class/leds/<led>/flash_brightness
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read/write
+		Set the brightness of this LED in the flash strobe mode, in
+		microamperes. The file is created only for the flash LED devices
+		that support setting flash brightness.
+
+		The value is between 0 and
+		/sys/class/leds/<led>/max_flash_brightness.
+
+What:		/sys/class/leds/<led>/max_flash_brightness
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read only
+		Maximum brightness level for this LED in the flash strobe mode,
+		in microamperes.
+
+What:		/sys/class/leds/<led>/flash_timeout
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read/write
+		Hardware timeout for flash, in microseconds. The flash strobe
+		is stopped after this period of time has passed from the start
+		of the strobe. The file is created only for the flash LED
+		devices that support setting flash timeout.
+
+What:		/sys/class/leds/<led>/max_flash_timeout
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read only
+		Maximum flash timeout for this LED, in microseconds.
+
+What:		/sys/class/leds/<led>/flash_strobe
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read/write
+		Flash strobe state. When written with 1 it triggers flash strobe
+		and when written with 0 it turns the flash off.
+
+		On read 1 means that flash is currently strobing and 0 means
+		that flash is off.
+
+What:		/sys/class/leds/<led>/flash_fault
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	Jacek Anaszewski <j.anaszewski@samsung.com>
+Description:	read only
+		Space separated list of flash faults that may have occurred.
+		Flash faults are re-read after strobing the flash. Possible
+		flash faults:
+
+		* led-over-voltage
+			flash controller voltage to the flash LED
+			has exceeded the limit specific to the flash controller
+		* flash-timeout-exceeded
+			the flash strobe was still on when
+			the timeout set by the user has expired; not all flash
+			controllers may set this in all such conditions
+		* controller-over-temperature
+			the flash controller has
+			overheated
+		* controller-short-circuit
+			the short circuit protection
+			of the flash controller has been triggered
+		* led-power-supply-over-current
+			current in the LED power
+			supply has exceeded the limit specific to the flash
+			controller
+		* indicator-led-fault
+			the flash controller has detected
+			a short or open circuit condition on the indicator LED
+		* led-under-voltage
+			flash controller voltage to the flash
+			LED has been below the minimum limit specific to
+			the flash
+		* controller-under-voltage
+			the input voltage of the flash
+			controller is below the limit under which strobing the
+			flash at full current will not be possible;
+			the condition persists until this flag is no longer set
+		* led-over-temperature
+			the temperature of the LED has exceeded
+			its allowed upper limit