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, 21 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-ec b/Documentation/ABI/testing/debugfs-ec
new file mode 100644
index 000000000..ab6099daa
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-ec
@@ -0,0 +1,21 @@
+What:		/sys/kernel/debug/ec/*/{gpe,use_global_lock,io}
+Date:		July 2010
+Contact:	Thomas Renninger <trenn@suse.de>
+Description:
+
+General information like which GPE is assigned to the EC and whether
+the global lock should get used.
+Knowing the EC GPE one can watch the amount of HW events related to
+the EC here (XY -> GPE number from `/sys/kernel/debug/ec/*/gpe`):
+/sys/firmware/acpi/interrupts/gpeXY
+
+The io file is binary and a userspace tool located here:
+ftp://ftp.suse.com/pub/people/trenn/sources/ec/
+should get used to read out the 256 Embedded Controller registers
+or writing to them.
+
+CAUTION:
+  Do not write to the Embedded Controller if you don't know
+  what you are doing! Rebooting afterwards also is a good idea.
+  This can influence the way your machine is cooled and fans may
+  not get switched on again after you did a wrong write.