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, 57 insertions, 0 deletions

diff --git a/tools/perf/util/capstone.h b/tools/perf/util/capstone.h
new file mode 100644
index 000000000..7c0baaa01
--- /dev/null
+++ b/tools/perf/util/capstone.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_CAPSTONE_H
+#define __PERF_CAPSTONE_H
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/compiler.h>
+#include <linux/types.h>
+
+struct annotate_args;
+struct machine;
+struct symbol;
+struct thread;
+
+#ifdef HAVE_LIBCAPSTONE_SUPPORT
+ssize_t capstone__fprintf_insn_asm(struct machine *machine, struct thread *thread, u8 cpumode,
+				   bool is64bit, const uint8_t *code, size_t code_size,
+				   uint64_t ip, int *lenp, int print_opts, FILE *fp);
+int symbol__disassemble_capstone(const char *filename, struct symbol *sym,
+				 struct annotate_args *args);
+int symbol__disassemble_capstone_powerpc(const char *filename, struct symbol *sym,
+					 struct annotate_args *args);
+
+#else /* !HAVE_LIBCAPSTONE_SUPPORT */
+static inline ssize_t capstone__fprintf_insn_asm(struct machine *machine __maybe_unused,
+						 struct thread *thread __maybe_unused,
+						 u8 cpumode __maybe_unused,
+						 bool is64bit __maybe_unused,
+						 const uint8_t *code __maybe_unused,
+						 size_t code_size __maybe_unused,
+						 uint64_t ip __maybe_unused,
+						 int *lenp __maybe_unused,
+						 int print_opts __maybe_unused,
+						 FILE *fp __maybe_unused)
+{
+	return -1;
+}
+
+static inline int symbol__disassemble_capstone(const char *filename __maybe_unused,
+					       struct symbol *sym __maybe_unused,
+					       struct annotate_args *args __maybe_unused)
+{
+	return -1;
+}
+
+static inline int symbol__disassemble_capstone_powerpc(const char *filename __maybe_unused,
+						       struct symbol *sym __maybe_unused,
+						       struct annotate_args *args __maybe_unused)
+{
+	return -1;
+}
+
+#endif /* HAVE_LIBCAPSTONE_SUPPORT */
+
+#endif /* __PERF_CAPSTONE_H */