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/include/scsi/scsicam.h b/include/scsi/scsicam.h
new file mode 100644
index 000000000..1131f51ed
--- /dev/null
+++ b/include/scsi/scsicam.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * scsicam.h - SCSI CAM support functions, use for HDIO_GETGEO, etc.
+ *
+ * Copyright 1993, 1994 Drew Eckhardt
+ *      Visionary Computing 
+ *      (Unix and Linux consulting and custom programming)
+ *      drew@Colorado.EDU
+ *	+1 (303) 786-7975
+ *
+ * For more information, please consult the SCSI-CAM draft.
+ */
+
+#ifndef SCSICAM_H
+#define SCSICAM_H
+struct gendisk;
+int scsicam_bios_param(struct gendisk *disk, sector_t capacity, int *ip);
+bool scsi_partsize(struct gendisk *disk, sector_t capacity, int geom[3]);
+unsigned char *scsi_bios_ptable(struct gendisk *disk);
+#endif /* def SCSICAM_H */