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/probe-file.h b/tools/perf/util/probe-file.h
new file mode 100644
index 000000000..c2bb6a5b9
--- /dev/null
+++ b/tools/perf/util/probe-file.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PROBE_FILE_H
+#define __PROBE_FILE_H
+
+#include "probe-event.h"
+
+struct strlist;
+struct strfilter;
+
+/* Cache of probe definitions */
+struct probe_cache_entry {
+	struct list_head	node;
+	bool			sdt;
+	struct perf_probe_event pev;
+	char			*spev;
+	struct strlist		*tevlist;
+};
+
+struct probe_cache {
+	int	fd;
+	struct list_head entries;
+};
+
+enum probe_type {
+	PROBE_TYPE_U = 0,
+	PROBE_TYPE_S,
+	PROBE_TYPE_X,
+	PROBE_TYPE_STRING,
+	PROBE_TYPE_BITFIELD,
+	PROBE_TYPE_END,
+};
+
+#define PF_FL_UPROBE	1
+#define PF_FL_RW	2
+#define for_each_probe_cache_entry(entry, pcache) \
+	list_for_each_entry(entry, &pcache->entries, node)
+
+/* probe-file.c depends on libelf */
+#ifdef HAVE_LIBELF_SUPPORT
+int open_trace_file(const char *trace_file, bool readwrite);
+int probe_file__open(int flag);
+int probe_file__open_both(int *kfd, int *ufd, int flag);
+struct strlist *probe_file__get_namelist(int fd);
+struct strlist *probe_file__get_rawlist(int fd);
+int probe_file__add_event(int fd, struct probe_trace_event *tev);
+
+int probe_file__get_events(int fd, struct strfilter *filter,
+				  struct strlist *plist);
+int probe_file__del_strlist(int fd, struct strlist *namelist);
+
+int probe_cache_entry__get_event(struct probe_cache_entry *entry,
+				 struct probe_trace_event **tevs);
+
+struct probe_cache *probe_cache__new(const char *target, struct nsinfo *nsi);
+int probe_cache__add_entry(struct probe_cache *pcache,
+			   struct perf_probe_event *pev,
+			   struct probe_trace_event *tevs, int ntevs);
+int probe_cache__scan_sdt(struct probe_cache *pcache, const char *pathname);
+int probe_cache__commit(struct probe_cache *pcache);
+void probe_cache__purge(struct probe_cache *pcache);
+void probe_cache__delete(struct probe_cache *pcache);
+int probe_cache__filter_purge(struct probe_cache *pcache,
+			      struct strfilter *filter);
+struct probe_cache_entry *probe_cache__find(struct probe_cache *pcache,
+					    struct perf_probe_event *pev);
+struct probe_cache_entry *probe_cache__find_by_name(struct probe_cache *pcache,
+					const char *group, const char *event);
+int probe_cache__show_all_caches(struct strfilter *filter);
+bool probe_type_is_available(enum probe_type type);
+bool kretprobe_offset_is_supported(void);
+bool uprobe_ref_ctr_is_supported(void);
+bool user_access_is_supported(void);
+bool multiprobe_event_is_supported(void);
+bool immediate_value_is_supported(void);
+#else	/* ! HAVE_LIBELF_SUPPORT */
+static inline struct probe_cache *probe_cache__new(const char *tgt __maybe_unused, struct nsinfo *nsi __maybe_unused)
+{
+	return NULL;
+}
+#define probe_cache__delete(pcache) do {} while (0)
+#endif
+#endif