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, 82 insertions, 0 deletions

diff --git a/tools/perf/util/libbfd.h b/tools/perf/util/libbfd.h
new file mode 100644
index 000000000..953886f3d
--- /dev/null
+++ b/tools/perf/util/libbfd.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_LIBBFD_H
+#define __PERF_LIBBFD_H
+
+#include <linux/compiler.h>
+#include <linux/types.h>
+#include <stdbool.h>
+#include <stddef.h>
+
+struct annotate_args;
+struct build_id;
+struct dso;
+struct inline_node;
+struct symbol;
+
+#ifdef HAVE_LIBBFD_SUPPORT
+int libbfd__addr2line(const char *dso_name, u64 addr,
+		char **file, unsigned int *line, struct dso *dso,
+		bool unwind_inlines, struct inline_node *node,
+		struct symbol *sym);
+
+
+void dso__free_a2l_libbfd(struct dso *dso);
+
+int symbol__disassemble_libbfd(const char *filename, struct symbol *sym,
+			     struct annotate_args *args);
+
+int libbfd__read_build_id(const char *filename, struct build_id *bid);
+
+int libbfd_filename__read_debuglink(const char *filename, char *debuglink, size_t size);
+
+int symbol__disassemble_bpf_libbfd(struct symbol *sym, struct annotate_args *args);
+
+#else // !defined(HAVE_LIBBFD_SUPPORT)
+#include "annotate.h"
+
+static inline int libbfd__addr2line(const char *dso_name __always_unused,
+				u64 addr __always_unused,
+				char **file __always_unused,
+				unsigned int *line __always_unused,
+				struct dso *dso __always_unused,
+				bool unwind_inlines __always_unused,
+				struct inline_node *node __always_unused,
+				struct symbol *sym __always_unused)
+{
+	return -1;
+}
+
+
+static inline void dso__free_a2l_libbfd(struct dso *dso __always_unused)
+{
+}
+
+static inline int symbol__disassemble_libbfd(const char *filename __always_unused,
+					struct symbol *sym __always_unused,
+					struct annotate_args *args __always_unused)
+{
+	return -1;
+}
+
+static inline int libbfd__read_build_id(const char *filename __always_unused,
+					struct build_id *bid __always_unused)
+{
+	return -1;
+}
+
+static inline int libbfd_filename__read_debuglink(const char *filename __always_unused,
+						char *debuglink __always_unused,
+						size_t size __always_unused)
+{
+	return -1;
+}
+
+static inline int symbol__disassemble_bpf_libbfd(struct symbol *sym __always_unused,
+						 struct annotate_args *args __always_unused)
+{
+	return SYMBOL_ANNOTATE_ERRNO__NO_LIBOPCODES_FOR_BPF;
+}
+
+#endif // defined(HAVE_LIBBFD_SUPPORT)
+
+#endif /* __PERF_LIBBFD_H */