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, 91 insertions, 0 deletions

diff --git a/tools/perf/util/compress.h b/tools/perf/util/compress.h
new file mode 100644
index 000000000..6cfecfca1
--- /dev/null
+++ b/tools/perf/util/compress.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef PERF_COMPRESS_H
+#define PERF_COMPRESS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <linux/compiler.h>
+#ifdef HAVE_ZSTD_SUPPORT
+#include <zstd.h>
+#endif
+
+#ifdef HAVE_ZLIB_SUPPORT
+int gzip_decompress_to_file(const char *input, int output_fd);
+bool gzip_is_compressed(const char *input);
+#endif
+
+#ifdef HAVE_LZMA_SUPPORT
+int lzma_decompress_stream_to_file(FILE *input, int output_fd);
+int lzma_decompress_to_file(const char *input, int output_fd);
+bool lzma_is_compressed(const char *input);
+#else
+static inline
+int lzma_decompress_stream_to_file(FILE *input __maybe_unused,
+				   int output_fd __maybe_unused)
+{
+	return -1;
+}
+static inline
+int lzma_decompress_to_file(const char *input __maybe_unused,
+			    int output_fd __maybe_unused)
+{
+	return -1;
+}
+static inline int lzma_is_compressed(const char *input __maybe_unused)
+{
+	return false;
+}
+#endif
+
+struct zstd_data {
+#ifdef HAVE_ZSTD_SUPPORT
+	ZSTD_CStream	*cstream;
+	ZSTD_DStream	*dstream;
+	int comp_level;
+#endif
+};
+
+#ifdef HAVE_ZSTD_SUPPORT
+
+int zstd_init(struct zstd_data *data, int level);
+int zstd_fini(struct zstd_data *data);
+
+ssize_t zstd_compress_stream_to_records(struct zstd_data *data, void *dst, size_t dst_size,
+				       void *src, size_t src_size, size_t max_record_size,
+				       size_t process_header(void *record, size_t increment));
+
+size_t zstd_decompress_stream(struct zstd_data *data, void *src, size_t src_size,
+			      void *dst, size_t dst_size);
+#else /* !HAVE_ZSTD_SUPPORT */
+
+static inline int zstd_init(struct zstd_data *data __maybe_unused, int level __maybe_unused)
+{
+	return 0;
+}
+
+static inline int zstd_fini(struct zstd_data *data __maybe_unused)
+{
+	return 0;
+}
+
+static inline
+ssize_t zstd_compress_stream_to_records(struct zstd_data *data __maybe_unused,
+				       void *dst __maybe_unused, size_t dst_size __maybe_unused,
+				       void *src __maybe_unused, size_t src_size __maybe_unused,
+				       size_t max_record_size __maybe_unused,
+				       size_t process_header(void *record, size_t increment) __maybe_unused)
+{
+	return 0;
+}
+
+static inline size_t zstd_decompress_stream(struct zstd_data *data __maybe_unused, void *src __maybe_unused,
+					    size_t src_size __maybe_unused, void *dst __maybe_unused,
+					    size_t dst_size __maybe_unused)
+{
+	return 0;
+}
+#endif
+
+#endif /* PERF_COMPRESS_H */