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, 151 insertions, 0 deletions

diff --git a/tools/perf/tests/thread-map.c b/tools/perf/tests/thread-map.c
new file mode 100644
index 000000000..877868107
--- /dev/null
+++ b/tools/perf/tests/thread-map.c
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <sys/prctl.h>
+#include "tests.h"
+#include "thread_map.h"
+#include "debug.h"
+#include "event.h"
+#include "util/synthetic-events.h"
+#include <perf/event.h>
+#include <internal/threadmap.h>
+
+struct perf_sample;
+struct perf_tool;
+struct machine;
+
+#define NAME	(const char *) "perf"
+#define NAMEUL	(unsigned long) NAME
+
+static int test__thread_map(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct perf_thread_map *map;
+
+	TEST_ASSERT_VAL("failed to set process name",
+			!prctl(PR_SET_NAME, NAMEUL, 0, 0, 0));
+
+	/* test map on current pid */
+	map = thread_map__new_by_pid(getpid());
+	TEST_ASSERT_VAL("failed to alloc map", map);
+
+	thread_map__read_comms(map);
+
+	TEST_ASSERT_VAL("wrong nr", map->nr == 1);
+	TEST_ASSERT_VAL("wrong pid",
+			perf_thread_map__pid(map, 0) == getpid());
+	TEST_ASSERT_VAL("wrong comm",
+			perf_thread_map__comm(map, 0) &&
+			!strcmp(perf_thread_map__comm(map, 0), NAME));
+	TEST_ASSERT_VAL("wrong refcnt",
+			refcount_read(&map->refcnt) == 1);
+	perf_thread_map__put(map);
+
+	/* test dummy pid */
+	map = perf_thread_map__new_dummy();
+	TEST_ASSERT_VAL("failed to alloc map", map);
+
+	thread_map__read_comms(map);
+
+	TEST_ASSERT_VAL("wrong nr", map->nr == 1);
+	TEST_ASSERT_VAL("wrong pid", perf_thread_map__pid(map, 0) == -1);
+	TEST_ASSERT_VAL("wrong comm",
+			perf_thread_map__comm(map, 0) &&
+			!strcmp(perf_thread_map__comm(map, 0), "dummy"));
+	TEST_ASSERT_VAL("wrong refcnt",
+			refcount_read(&map->refcnt) == 1);
+	perf_thread_map__put(map);
+	return 0;
+}
+
+static int process_event(const struct perf_tool *tool __maybe_unused,
+			 union perf_event *event,
+			 struct perf_sample *sample __maybe_unused,
+			 struct machine *machine __maybe_unused)
+{
+	struct perf_record_thread_map *map = &event->thread_map;
+	struct perf_thread_map *threads;
+
+	TEST_ASSERT_VAL("wrong nr",   map->nr == 1);
+	TEST_ASSERT_VAL("wrong pid",  map->entries[0].pid == (u64) getpid());
+	TEST_ASSERT_VAL("wrong comm", !strcmp(map->entries[0].comm, NAME));
+
+	threads = thread_map__new_event(&event->thread_map);
+	TEST_ASSERT_VAL("failed to alloc map", threads);
+
+	TEST_ASSERT_VAL("wrong nr", threads->nr == 1);
+	TEST_ASSERT_VAL("wrong pid",
+			perf_thread_map__pid(threads, 0) == getpid());
+	TEST_ASSERT_VAL("wrong comm",
+			perf_thread_map__comm(threads, 0) &&
+			!strcmp(perf_thread_map__comm(threads, 0), NAME));
+	TEST_ASSERT_VAL("wrong refcnt",
+			refcount_read(&threads->refcnt) == 1);
+	perf_thread_map__put(threads);
+	return 0;
+}
+
+static int test__thread_map_synthesize(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct perf_thread_map *threads;
+
+	TEST_ASSERT_VAL("failed to set process name",
+			!prctl(PR_SET_NAME, NAMEUL, 0, 0, 0));
+
+	/* test map on current pid */
+	threads = thread_map__new_by_pid(getpid());
+	TEST_ASSERT_VAL("failed to alloc map", threads);
+
+	thread_map__read_comms(threads);
+
+	TEST_ASSERT_VAL("failed to synthesize map",
+		!perf_event__synthesize_thread_map2(NULL, threads, process_event, NULL));
+
+	perf_thread_map__put(threads);
+	return 0;
+}
+
+static int test__thread_map_remove(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct perf_thread_map *threads;
+	char *str;
+
+	TEST_ASSERT_VAL("failed to allocate map string",
+			asprintf(&str, "%d,%d", getpid(), getppid()) >= 0);
+
+	threads = thread_map__new_str(str, /*tid=*/NULL, /*all_threads=*/false);
+	free(str);
+
+	TEST_ASSERT_VAL("failed to allocate thread_map",
+			threads);
+
+	if (verbose > 0)
+		thread_map__fprintf(threads, stderr);
+
+	TEST_ASSERT_VAL("failed to remove thread",
+			!thread_map__remove(threads, 0));
+
+	TEST_ASSERT_VAL("thread_map count != 1", threads->nr == 1);
+
+	if (verbose > 0)
+		thread_map__fprintf(threads, stderr);
+
+	TEST_ASSERT_VAL("failed to remove thread",
+			!thread_map__remove(threads, 0));
+
+	TEST_ASSERT_VAL("thread_map count != 0", threads->nr == 0);
+
+	if (verbose > 0)
+		thread_map__fprintf(threads, stderr);
+
+	TEST_ASSERT_VAL("failed to not remove thread",
+			thread_map__remove(threads, 0));
+
+	perf_thread_map__put(threads);
+	return 0;
+}
+
+DEFINE_SUITE("Thread map", thread_map);
+DEFINE_SUITE("Synthesize thread map", thread_map_synthesize);
+DEFINE_SUITE("Remove thread map", thread_map_remove);