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, 35 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-net-grcan b/Documentation/ABI/testing/sysfs-class-net-grcan
new file mode 100644
index 000000000..f418c92ca
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-net-grcan
@@ -0,0 +1,35 @@
+
+What:		/sys/class/net/<iface>/grcan/enable0
+Date:		October 2012
+KernelVersion:	3.8
+Contact:	Andreas Larsson <andreas@gaisler.com>
+Description:
+		Hardware configuration of physical interface 0. This file reads
+		and writes the "Enable 0" bit of the configuration register.
+		Possible values: 0 or 1. See the GRCAN chapter of the GRLIB IP
+		core library documentation for details. The default value is 0
+		or set by the module parameter grcan.enable0 and can be read at
+		/sys/module/grcan/parameters/enable0.
+
+What:		/sys/class/net/<iface>/grcan/enable1
+Date:		October 2012
+KernelVersion:	3.8
+Contact:	Andreas Larsson <andreas@gaisler.com>
+Description:
+		Hardware configuration of physical interface 1. This file reads
+		and writes the "Enable 1" bit of the configuration register.
+		Possible values: 0 or 1. See the GRCAN chapter of the GRLIB IP
+		core library documentation for details. The default value is 0
+		or set by the module parameter grcan.enable1 and can be read at
+		/sys/module/grcan/parameters/enable1.
+
+What:		/sys/class/net/<iface>/grcan/select
+Date:		October 2012
+KernelVersion:	3.8
+Contact:	Andreas Larsson <andreas@gaisler.com>
+Description:
+		Configuration of which physical interface to be used. Possible
+		values: 0 or 1. See the GRCAN chapter of the GRLIB IP core
+		library documentation for details. The default value is 0 or is
+		set by the module parameter grcan.select and can be read at
+		/sys/module/grcan/parameters/select.