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, 126 insertions, 0 deletions

diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
new file mode 100644
index 000000000..87a0818a8
--- /dev/null
+++ b/tools/perf/util/util.h
@@ -0,0 +1,126 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_UTIL_H
+#define __PERF_UTIL_H
+
+#define _BSD_SOURCE 1
+/* glibc 2.20 deprecates _BSD_SOURCE in favour of _DEFAULT_SOURCE */
+#define _DEFAULT_SOURCE 1
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <linux/compiler.h>
+#include <linux/bitmap.h>
+#include <sys/types.h>
+#ifndef __cplusplus
+#include <internal/cpumap.h>
+#endif
+
+extern const char perf_usage_string[];
+extern const char perf_more_info_string[];
+
+extern const char *input_name;
+
+/* This will control if perf_{host,guest} will set attr.exclude_{host,guest}. */
+extern bool exclude_GH_default;
+
+extern bool perf_host;
+extern bool perf_guest;
+
+/* General helper functions */
+void usage(const char *err) __noreturn;
+
+struct dirent;
+struct strlist;
+
+int mkdir_p(char *path, mode_t mode);
+int rm_rf(const char *path);
+int rm_rf_perf_data(const char *path);
+struct strlist *lsdir(const char *name, bool (*filter)(const char *, struct dirent *));
+bool lsdir_no_dot_filter(const char *name, struct dirent *d);
+
+size_t hex_width(u64 v);
+
+int sysctl__max_stack(void);
+
+bool sysctl__nmi_watchdog_enabled(void);
+
+int perf_tip(char **strp, const char *dirpath);
+
+void cpumask_to_cpulist(char *cpumask, char *cpulist);
+
+void print_separator2(int pre_dash_cnt, const char *s, int post_dash_cnt);
+
+#ifndef HAVE_SCHED_GETCPU_SUPPORT
+int sched_getcpu(void);
+#endif
+
+#ifndef HAVE_SCANDIRAT_SUPPORT
+int scandirat(int dirfd, const char *dirp,
+	      struct dirent ***namelist,
+	      int (*filter)(const struct dirent *),
+	      int (*compar)(const struct dirent **, const struct dirent **));
+#endif
+
+extern bool perf_singlethreaded;
+
+void perf_set_singlethreaded(void);
+void perf_set_multithreaded(void);
+
+char *perf_exe(char *buf, int len);
+
+#ifndef O_CLOEXEC
+#ifdef __sparc__
+#define O_CLOEXEC      0x400000
+#elif defined(__alpha__) || defined(__hppa__)
+#define O_CLOEXEC      010000000
+#else
+#define O_CLOEXEC      02000000
+#endif
+#endif
+
+struct perf_debuginfod {
+	const char	*urls;
+	bool		 set;
+};
+void perf_debuginfod_setup(struct perf_debuginfod *di);
+
+const char *perf_basename(const char *path);
+
+char *filename_with_chroot(int pid, const char *filename);
+
+int do_realloc_array_as_needed(void **arr, size_t *arr_sz, size_t x,
+			       size_t msz, const void *init_val);
+
+#define realloc_array_as_needed(a, n, x, v) ({			\
+	typeof(x) __x = (x);					\
+	__x >= (n) ?						\
+		do_realloc_array_as_needed((void **)&(a),	\
+					   &(n),		\
+					   __x,			\
+					   sizeof(*(a)),	\
+					   (const void *)(v)) :	\
+		0;						\
+	})
+
+static inline bool host_is_bigendian(void)
+{
+#ifdef __BYTE_ORDER__
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	return false;
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	return true;
+#else
+#error "Unrecognized __BYTE_ORDER__"
+#endif
+#else /* !__BYTE_ORDER__ */
+	unsigned char str[] = { 0x1, 0x2, 0x3, 0x4, 0x0, 0x0, 0x0, 0x0};
+	unsigned int *ptr;
+
+	ptr = (unsigned int *)(void *)str;
+	return *ptr == 0x01020304;
+#endif
+}
+
+#endif /* __PERF_UTIL_H */