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, 253 insertions, 0 deletions

diff --git a/tools/perf/tests/time-utils-test.c b/tools/perf/tests/time-utils-test.c
new file mode 100644
index 000000000..38df10373
--- /dev/null
+++ b/tools/perf/tests/time-utils-test.c
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <linux/time64.h>
+#include <inttypes.h>
+#include <string.h>
+#include "time-utils.h"
+#include "evlist.h"
+#include "session.h"
+#include "debug.h"
+#include "tests.h"
+
+static bool test__parse_nsec_time(const char *str, u64 expected)
+{
+	u64 ptime;
+	int err;
+
+	pr_debug("\nparse_nsec_time(\"%s\")\n", str);
+
+	err = parse_nsec_time(str, &ptime);
+	if (err) {
+		pr_debug("error %d\n", err);
+		return false;
+	}
+
+	if (ptime != expected) {
+		pr_debug("Failed. ptime %" PRIu64 " expected %" PRIu64 "\n",
+			 ptime, expected);
+		return false;
+	}
+
+	pr_debug("%" PRIu64 "\n", ptime);
+
+	return true;
+}
+
+static bool test__perf_time__parse_str(const char *ostr, u64 start, u64 end)
+{
+	struct perf_time_interval ptime;
+	int err;
+
+	pr_debug("\nperf_time__parse_str(\"%s\")\n", ostr);
+
+	err = perf_time__parse_str(&ptime, ostr);
+	if (err) {
+		pr_debug("Error %d\n", err);
+		return false;
+	}
+
+	if (ptime.start != start || ptime.end != end) {
+		pr_debug("Failed. Expected %" PRIu64 " to %" PRIu64 "\n",
+			 start, end);
+		return false;
+	}
+
+	return true;
+}
+
+#define TEST_MAX 64
+
+struct test_data {
+	const char *str;
+	u64 first;
+	u64 last;
+	struct perf_time_interval ptime[TEST_MAX];
+	int num;
+	u64 skip[TEST_MAX];
+	u64 noskip[TEST_MAX];
+};
+
+static bool test__perf_time__parse_for_ranges(struct test_data *d)
+{
+	struct evlist evlist = {
+		.first_sample_time = d->first,
+		.last_sample_time = d->last,
+	};
+	struct perf_session session = { .evlist = &evlist };
+	struct perf_time_interval *ptime = NULL;
+	int range_size, range_num;
+	bool pass = false;
+	int i, err;
+
+	pr_debug("\nperf_time__parse_for_ranges(\"%s\")\n", d->str);
+
+	if (strchr(d->str, '%'))
+		pr_debug("first_sample_time %" PRIu64 " last_sample_time %" PRIu64 "\n",
+			 d->first, d->last);
+
+	err = perf_time__parse_for_ranges(d->str, &session, &ptime, &range_size,
+					  &range_num);
+	if (err) {
+		pr_debug("error %d\n", err);
+		goto out;
+	}
+
+	if (range_size < d->num || range_num != d->num) {
+		pr_debug("bad size: range_size %d range_num %d expected num %d\n",
+			 range_size, range_num, d->num);
+		goto out;
+	}
+
+	for (i = 0; i < d->num; i++) {
+		if (ptime[i].start != d->ptime[i].start ||
+		    ptime[i].end != d->ptime[i].end) {
+			pr_debug("bad range %d expected %" PRIu64 " to %" PRIu64 "\n",
+				 i, d->ptime[i].start, d->ptime[i].end);
+			goto out;
+		}
+	}
+
+	if (perf_time__ranges_skip_sample(ptime, d->num, 0)) {
+		pr_debug("failed to keep 0\n");
+		goto out;
+	}
+
+	for (i = 0; i < TEST_MAX; i++) {
+		if (d->skip[i] &&
+		    !perf_time__ranges_skip_sample(ptime, d->num, d->skip[i])) {
+			pr_debug("failed to skip %" PRIu64 "\n", d->skip[i]);
+			goto out;
+		}
+		if (d->noskip[i] &&
+		    perf_time__ranges_skip_sample(ptime, d->num, d->noskip[i])) {
+			pr_debug("failed to keep %" PRIu64 "\n", d->noskip[i]);
+			goto out;
+		}
+	}
+
+	pass = true;
+out:
+	free(ptime);
+	return pass;
+}
+
+static int test__time_utils(struct test_suite *t __maybe_unused, int subtest __maybe_unused)
+{
+	bool pass = true;
+
+	pass &= test__parse_nsec_time("0", 0);
+	pass &= test__parse_nsec_time("1", 1000000000ULL);
+	pass &= test__parse_nsec_time("0.000000001", 1);
+	pass &= test__parse_nsec_time("1.000000001", 1000000001ULL);
+	pass &= test__parse_nsec_time("123456.123456", 123456123456000ULL);
+	pass &= test__parse_nsec_time("1234567.123456789", 1234567123456789ULL);
+	pass &= test__parse_nsec_time("18446744073.709551615",
+				      0xFFFFFFFFFFFFFFFFULL);
+
+	pass &= test__perf_time__parse_str("1234567.123456789,1234567.123456789",
+					   1234567123456789ULL, 1234567123456789ULL);
+	pass &= test__perf_time__parse_str("1234567.123456789,1234567.123456790",
+					   1234567123456789ULL, 1234567123456790ULL);
+	pass &= test__perf_time__parse_str("1234567.123456789,",
+					   1234567123456789ULL, 0);
+	pass &= test__perf_time__parse_str(",1234567.123456789",
+					   0, 1234567123456789ULL);
+	pass &= test__perf_time__parse_str("0,1234567.123456789",
+					   0, 1234567123456789ULL);
+
+	{
+		u64 b = 1234567123456789ULL;
+		struct test_data d = {
+			.str   = "1234567.123456789,1234567.123456790",
+			.ptime = { {b, b + 1}, },
+			.num = 1,
+			.skip = { b - 1, b + 2, },
+			.noskip = { b, b + 1, },
+		};
+
+		pass &= test__perf_time__parse_for_ranges(&d);
+	}
+
+	{
+		u64 b = 1234567123456789ULL;
+		u64 c = 7654321987654321ULL;
+		u64 e = 8000000000000000ULL;
+		struct test_data d = {
+			.str   = "1234567.123456789,1234567.123456790 "
+				 "7654321.987654321,7654321.987654444 "
+				 "8000000,8000000.000000005",
+			.ptime = { {b, b + 1}, {c, c + 123}, {e, e + 5}, },
+			.num = 3,
+			.skip = { b - 1, b + 2, c - 1, c + 124, e - 1, e + 6 },
+			.noskip = { b, b + 1, c, c + 123, e, e + 5 },
+		};
+
+		pass &= test__perf_time__parse_for_ranges(&d);
+	}
+
+	{
+		u64 b = 7654321ULL * NSEC_PER_SEC;
+		struct test_data d = {
+			.str    = "10%/1",
+			.first  = b,
+			.last   = b + 100,
+			.ptime  = { {b, b + 9}, },
+			.num    = 1,
+			.skip   = { b - 1, b + 10, },
+			.noskip = { b, b + 9, },
+		};
+
+		pass &= test__perf_time__parse_for_ranges(&d);
+	}
+
+	{
+		u64 b = 7654321ULL * NSEC_PER_SEC;
+		struct test_data d = {
+			.str    = "10%/2",
+			.first  = b,
+			.last   = b + 100,
+			.ptime  = { {b + 10, b + 19}, },
+			.num    = 1,
+			.skip   = { b + 9, b + 20, },
+			.noskip = { b + 10, b + 19, },
+		};
+
+		pass &= test__perf_time__parse_for_ranges(&d);
+	}
+
+	{
+		u64 b = 11223344ULL * NSEC_PER_SEC;
+		struct test_data d = {
+			.str    = "10%/1,10%/2",
+			.first  = b,
+			.last   = b + 100,
+			.ptime  = { {b, b + 9}, {b + 10, b + 19}, },
+			.num    = 2,
+			.skip   = { b - 1, b + 20, },
+			.noskip = { b, b + 8, b + 9, b + 10, b + 11, b + 12, b + 19, },
+		};
+
+		pass &= test__perf_time__parse_for_ranges(&d);
+	}
+
+	{
+		u64 b = 11223344ULL * NSEC_PER_SEC;
+		struct test_data d = {
+			.str    = "10%/1,10%/3,10%/10",
+			.first  = b,
+			.last   = b + 100,
+			.ptime  = { {b, b + 9}, {b + 20, b + 29}, { b + 90, b + 100}, },
+			.num    = 3,
+			.skip   = { b - 1, b + 10, b + 19, b + 30, b + 89, b + 101 },
+			.noskip = { b, b + 9, b + 20, b + 29, b + 90, b + 100},
+		};
+
+		pass &= test__perf_time__parse_for_ranges(&d);
+	}
+
+	pr_debug("\n");
+
+	return pass ? 0 : TEST_FAIL;
+}
+
+DEFINE_SUITE("time utils", time_utils);