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, 20 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/procfs-attr-exec b/Documentation/ABI/testing/procfs-attr-exec
new file mode 100644
index 000000000..34593866a
--- /dev/null
+++ b/Documentation/ABI/testing/procfs-attr-exec
@@ -0,0 +1,20 @@
+What:		/proc/*/attr/exec
+Contact:	linux-security-module@vger.kernel.org,
+		selinux@vger.kernel.org,
+		apparmor@lists.ubuntu.com
+Description:	The security information to be used on the process
+		by a Linux security module (LSM) active on the system
+		after a subsequent exec() call.
+		The details of permissions required to read from
+		this interface and hence obtain the security state
+		of the task identified is LSM dependent.
+		A process cannot write to this interface unless it
+		refers to itself.
+		The other details of permissions required to write to
+		this interface and hence change the security state of
+		the task identified are LSM dependent.
+		The format of the data used by this interface is LSM
+		dependent.
+		SELinux and AppArmor provide this interface.
+Users:		SELinux user-space
+		AppArmor user-space