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, 121 insertions, 0 deletions

diff --git a/tools/perf/tests/stat.c b/tools/perf/tests/stat.c
new file mode 100644
index 000000000..d60983657
--- /dev/null
+++ b/tools/perf/tests/stat.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include "event.h"
+#include "tests.h"
+#include "stat.h"
+#include "counts.h"
+#include "debug.h"
+#include "util/synthetic-events.h"
+
+static bool has_term(struct perf_record_stat_config *config,
+		     u64 tag, u64 val)
+{
+	unsigned i;
+
+	for (i = 0; i < config->nr; i++) {
+		if ((config->data[i].tag == tag) &&
+		    (config->data[i].val == val))
+			return true;
+	}
+
+	return false;
+}
+
+static int process_stat_config_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_stat_config *config = &event->stat_config;
+	struct perf_stat_config test_stat_config = {};
+
+#define HAS(term, val) \
+	has_term(config, PERF_STAT_CONFIG_TERM__##term, val)
+
+	TEST_ASSERT_VAL("wrong nr",        config->nr == PERF_STAT_CONFIG_TERM__MAX);
+	TEST_ASSERT_VAL("wrong aggr_mode", HAS(AGGR_MODE, AGGR_CORE));
+	TEST_ASSERT_VAL("wrong scale",     HAS(SCALE, 1));
+	TEST_ASSERT_VAL("wrong interval",  HAS(INTERVAL, 1));
+
+#undef HAS
+
+	perf_event__read_stat_config(&test_stat_config, config);
+
+	TEST_ASSERT_VAL("wrong aggr_mode", test_stat_config.aggr_mode == AGGR_CORE);
+	TEST_ASSERT_VAL("wrong scale",     test_stat_config.scale == 1);
+	TEST_ASSERT_VAL("wrong interval",  test_stat_config.interval == 1);
+	return 0;
+}
+
+static int test__synthesize_stat_config(struct test_suite *test __maybe_unused,
+					int subtest __maybe_unused)
+{
+	struct perf_stat_config test_stat_config = {
+		.aggr_mode	= AGGR_CORE,
+		.scale		= 1,
+		.interval	= 1,
+	};
+
+	TEST_ASSERT_VAL("failed to synthesize stat_config",
+		!perf_event__synthesize_stat_config(NULL, &test_stat_config,
+						    process_stat_config_event,
+						    NULL));
+
+	return 0;
+}
+
+static int process_stat_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_stat *st = &event->stat;
+
+	TEST_ASSERT_VAL("wrong cpu",    st->cpu    == 1);
+	TEST_ASSERT_VAL("wrong thread", st->thread == 2);
+	TEST_ASSERT_VAL("wrong id",     st->id     == 3);
+	TEST_ASSERT_VAL("wrong val",    st->val    == 100);
+	TEST_ASSERT_VAL("wrong run",    st->ena    == 200);
+	TEST_ASSERT_VAL("wrong ena",    st->run    == 300);
+	return 0;
+}
+
+static int test__synthesize_stat(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct perf_counts_values count;
+
+	count.val = 100;
+	count.ena = 200;
+	count.run = 300;
+
+	TEST_ASSERT_VAL("failed to synthesize stat_config",
+			!perf_event__synthesize_stat(NULL, (struct perf_cpu){.cpu = 1}, 2, 3,
+						     &count, process_stat_event, NULL));
+
+	return 0;
+}
+
+static int process_stat_round_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_stat_round *stat_round = &event->stat_round;
+
+	TEST_ASSERT_VAL("wrong time", stat_round->time == 0xdeadbeef);
+	TEST_ASSERT_VAL("wrong type", stat_round->type == PERF_STAT_ROUND_TYPE__INTERVAL);
+	return 0;
+}
+
+static int test__synthesize_stat_round(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	TEST_ASSERT_VAL("failed to synthesize stat_config",
+		!perf_event__synthesize_stat_round(NULL, 0xdeadbeef, PERF_STAT_ROUND_TYPE__INTERVAL,
+						   process_stat_round_event, NULL));
+
+	return 0;
+}
+
+DEFINE_SUITE("Synthesize stat config", synthesize_stat_config);
+DEFINE_SUITE("Synthesize stat", synthesize_stat);
+DEFINE_SUITE("Synthesize stat round", synthesize_stat_round);