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, 64 insertions, 0 deletions

diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h
new file mode 100644
index 000000000..4d72c5fa5
--- /dev/null
+++ b/tools/perf/util/mmap.h
@@ -0,0 +1,64 @@
+#ifndef __PERF_MMAP_H
+#define __PERF_MMAP_H 1
+
+#include <internal/mmap.h>
+#include <linux/types.h>
+#include <linux/bitops.h>
+#include <perf/cpumap.h>
+#ifdef HAVE_AIO_SUPPORT
+#include <aio.h>
+#endif
+#include "auxtrace.h"
+#include "util/compress.h"
+
+struct aiocb;
+
+struct mmap_cpu_mask {
+	unsigned long *bits;
+	size_t nbits;
+};
+
+#define MMAP_CPU_MASK_BYTES(m) \
+	(BITS_TO_LONGS(((struct mmap_cpu_mask *)m)->nbits) * sizeof(unsigned long))
+
+/**
+ * struct mmap - perf's ring buffer mmap details
+ *
+ * @refcnt - e.g. code using PERF_EVENT_IOC_SET_OUTPUT to share this
+ */
+struct mmap {
+	struct perf_mmap	core;
+	struct auxtrace_mmap auxtrace_mmap;
+#ifdef HAVE_AIO_SUPPORT
+	struct {
+		void		 **data;
+		struct aiocb	 *cblocks;
+		struct aiocb	 **aiocb;
+		int		 nr_cblocks;
+	} aio;
+#endif
+	struct mmap_cpu_mask	affinity_mask;
+	void		*data;
+	struct perf_data_file *file;
+	struct zstd_data      zstd_data;
+};
+
+struct mmap_params {
+	struct perf_mmap_param core;
+	int nr_cblocks, affinity, flush, comp_level;
+	struct auxtrace_mmap_params auxtrace_mp;
+};
+
+int mmap__mmap(struct mmap *map, struct mmap_params *mp, int fd, struct perf_cpu cpu);
+void mmap__munmap(struct mmap *map);
+
+union perf_event *perf_mmap__read_forward(struct mmap *map);
+
+int perf_mmap__push(struct mmap *md, void *to,
+		    int push(struct mmap *map, void *to, void *buf, size_t size));
+
+size_t mmap__mmap_len(struct mmap *map);
+
+void mmap_cpu_mask__scnprintf(struct mmap_cpu_mask *mask, const char *tag);
+
+#endif /*__PERF_MMAP_H */