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, 225 insertions, 0 deletions

diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
new file mode 100644
index 000000000..86b1a7202
--- /dev/null
+++ b/tools/perf/util/header.h
@@ -0,0 +1,225 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_HEADER_H
+#define __PERF_HEADER_H
+
+#include <linux/stddef.h>
+#include <linux/perf_event.h>
+#include <sys/types.h>
+#include <stdio.h> // FILE
+#include <stdbool.h>
+#include <linux/bitmap.h>
+#include <linux/types.h>
+#include "env.h"
+#include <perf/cpumap.h>
+
+struct evlist;
+union perf_event;
+struct perf_header;
+struct perf_session;
+struct perf_tool;
+
+enum {
+	HEADER_RESERVED		= 0,	/* always cleared */
+	HEADER_FIRST_FEATURE	= 1,
+	HEADER_TRACING_DATA	= 1,
+	HEADER_BUILD_ID,
+
+	HEADER_HOSTNAME,
+	HEADER_OSRELEASE,
+	HEADER_VERSION,
+	HEADER_ARCH,
+	HEADER_NRCPUS,
+	HEADER_CPUDESC,
+	HEADER_CPUID,
+	HEADER_TOTAL_MEM,
+	HEADER_CMDLINE,
+	HEADER_EVENT_DESC,
+	HEADER_CPU_TOPOLOGY,
+	HEADER_NUMA_TOPOLOGY,
+	HEADER_BRANCH_STACK,
+	HEADER_PMU_MAPPINGS,
+	HEADER_GROUP_DESC,
+	HEADER_AUXTRACE,
+	HEADER_STAT,
+	HEADER_CACHE,
+	HEADER_SAMPLE_TIME,
+	HEADER_MEM_TOPOLOGY,
+	HEADER_CLOCKID,
+	HEADER_DIR_FORMAT,
+	HEADER_BPF_PROG_INFO,
+	HEADER_BPF_BTF,
+	HEADER_COMPRESSED,
+	HEADER_CPU_PMU_CAPS,
+	HEADER_CLOCK_DATA,
+	HEADER_HYBRID_TOPOLOGY,
+	HEADER_PMU_CAPS,
+	HEADER_CPU_DOMAIN_INFO,
+	HEADER_E_MACHINE,
+	HEADER_CLN_SIZE,
+	HEADER_LAST_FEATURE,
+	HEADER_FEAT_BITS	= 256,
+};
+
+enum perf_header_version {
+	PERF_HEADER_VERSION_1,
+	PERF_HEADER_VERSION_2,
+};
+
+struct perf_file_section {
+	u64 offset;
+	u64 size;
+};
+
+/**
+ * struct perf_file_header: Header representation on disk.
+ */
+struct perf_file_header {
+	/** @magic: Holds "PERFILE2". */
+	u64				magic;
+	/** @size: Size of this header - sizeof(struct perf_file_header). */
+	u64				size;
+	/**
+	 * @attr_size: Size of attrs entries - sizeof(struct perf_event_attr) +
+	 * sizeof(struct perf_file_section).
+	 */
+	u64				attr_size;
+	/** @attrs: Offset and size of file section holding attributes. */
+	struct perf_file_section	attrs;
+	/** @data: Offset and size of file section holding regular event data. */
+	struct perf_file_section	data;
+	/** @event_types: Ignored. */
+	struct perf_file_section	event_types;
+	/**
+	 * @adds_features: Bitmap of features. The features are immediately after the data section.
+	 */
+	DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
+};
+
+struct perf_pipe_file_header {
+	u64				magic;
+	u64				size;
+};
+
+int perf_file_header__read(struct perf_file_header *header,
+			   struct perf_header *ph, int fd);
+
+struct perf_header {
+	enum perf_header_version	version;
+	bool				needs_swap;
+	u64				data_offset;
+	u64				data_size;
+	u64				feat_offset;
+	DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
+	int				last_feat;
+	struct perf_env 	env;
+};
+
+struct feat_fd {
+	struct perf_header *ph;
+	int		   fd;
+	void		   *buf;	/* Either buf != NULL or fd >= 0 */
+	ssize_t		   offset;
+	size_t		   size;
+	struct evsel	   *events;
+};
+
+struct perf_header_feature_ops {
+	int	   (*write)(struct feat_fd *ff, struct evlist *evlist);
+	void	   (*print)(struct feat_fd *ff, FILE *fp);
+	int	   (*process)(struct feat_fd *ff, void *data);
+	const char *name;
+	bool	   full_only;
+	bool	   synthesize;
+};
+
+extern const char perf_version_string[];
+
+const char *header_feat__name(unsigned int id);
+
+int perf_session__read_header(struct perf_session *session);
+int perf_session__write_header(struct perf_session *session,
+			       struct evlist *evlist,
+			       int fd, bool at_exit);
+int perf_header__write_pipe(int fd);
+
+/* feat_writer writes a feature section to output */
+struct feat_writer {
+	int (*write)(struct feat_writer *fw, void *buf, size_t sz);
+};
+
+/* feat_copier copies a feature section using feat_writer to output */
+struct feat_copier {
+	int (*copy)(struct feat_copier *fc, int feat, struct feat_writer *fw);
+};
+
+int perf_session__inject_header(struct perf_session *session,
+				struct evlist *evlist,
+				int fd,
+				struct feat_copier *fc,
+				bool write_attrs_after_data);
+
+size_t perf_session__data_offset(const struct evlist *evlist);
+
+void perf_header__set_feat(struct perf_header *header, int feat);
+void perf_header__clear_feat(struct perf_header *header, int feat);
+bool perf_header__has_feat(const struct perf_header *header, int feat);
+
+int perf_header__set_cmdline(int argc, const char **argv);
+
+int perf_header__process_sections(struct perf_header *header, int fd,
+				  void *data,
+				  int (*process)(struct perf_file_section *section,
+				  struct perf_header *ph,
+				  int feat, int fd, void *data));
+
+int perf_header__fprintf_info(struct perf_session *s, FILE *fp, bool full);
+
+int perf_event__process_feature(const struct perf_tool *tool,
+				struct perf_session *session,
+				union perf_event *event);
+int perf_event__process_attr(const struct perf_tool *tool, union perf_event *event,
+			     struct evlist **pevlist);
+int perf_event__process_event_update(const struct perf_tool *tool,
+				     union perf_event *event,
+				     struct evlist **pevlist);
+size_t perf_event__fprintf_attr(union perf_event *event, FILE *fp);
+size_t perf_event__fprintf_event_update(union perf_event *event, FILE *fp);
+#ifdef HAVE_LIBTRACEEVENT
+int perf_event__process_tracing_data(const struct perf_tool *tool,
+				     struct perf_session *session,
+				     union perf_event *event);
+#endif
+int perf_event__process_build_id(const struct perf_tool *tool,
+				 struct perf_session *session,
+				 union perf_event *event);
+bool is_perf_magic(u64 magic);
+
+#define NAME_ALIGN 64
+
+struct feat_fd;
+
+int do_write(struct feat_fd *fd, const void *buf, size_t size);
+
+int write_padded(struct feat_fd *fd, const void *bf,
+		 size_t count, size_t count_aligned);
+
+#define MAX_CACHE_LVL 4
+
+int build_caches_for_cpu(u32 cpu, struct cpu_cache_level caches[], u32 *cntp);
+
+#define DEFAULT_CACHELINE_SIZE 64
+
+/*
+ * arch specific callback
+ */
+int get_cpuid(char *buffer, size_t sz, struct perf_cpu cpu);
+
+char *get_cpuid_str(struct perf_cpu cpu);
+
+char *get_cpuid_allow_env_override(struct perf_cpu cpu);
+
+int strcmp_cpuid_str(const char *s1, const char *s2);
+
+struct cpu_domain_map **build_cpu_domain_map(u32 *schedstat_version, u32 *max_sched_domains,
+					     u32 nr);
+#endif /* __PERF_HEADER_H */