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, 343 insertions, 0 deletions

diff --git a/tools/perf/tests/api-io.c b/tools/perf/tests/api-io.c
new file mode 100644
index 000000000..0ba3d5cce
--- /dev/null
+++ b/tools/perf/tests/api-io.c
@@ -0,0 +1,343 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "debug.h"
+#include "tests.h"
+#include <api/io.h>
+#include <linux/kernel.h>
+#include <linux/zalloc.h>
+
+#define TEMPL "/tmp/perf-test-XXXXXX"
+
+#define EXPECT_EQUAL(val, expected)                             \
+do {								\
+	if (val != expected) {					\
+		pr_debug("%s:%d: %d != %d\n",			\
+			__FILE__, __LINE__, val, expected);	\
+		ret = -1;					\
+	}							\
+} while (0)
+
+#define EXPECT_EQUAL64(val, expected)                           \
+do {								\
+	if (val != expected) {					\
+		pr_debug("%s:%d: %lld != %lld\n",		\
+			__FILE__, __LINE__, val, expected);	\
+		ret = -1;					\
+	}							\
+} while (0)
+
+static int make_test_file(char path[PATH_MAX], const char *contents)
+{
+	ssize_t contents_len = strlen(contents);
+	int fd;
+
+	strcpy(path, TEMPL);
+	fd = mkstemp(path);
+	if (fd < 0) {
+		pr_debug("mkstemp failed");
+		return -1;
+	}
+	if (write(fd, contents, contents_len) < contents_len) {
+		pr_debug("short write");
+		close(fd);
+		unlink(path);
+		return -1;
+	}
+	close(fd);
+	return 0;
+}
+
+static int setup_test(char path[PATH_MAX], const char *contents,
+		      size_t buf_size, struct io *io)
+{
+	if (make_test_file(path, contents))
+		return -1;
+
+	io->fd = open(path, O_RDONLY);
+	if (io->fd < 0) {
+		pr_debug("Failed to open '%s'\n", path);
+		unlink(path);
+		return -1;
+	}
+	io->buf = malloc(buf_size);
+	if (io->buf == NULL) {
+		pr_debug("Failed to allocate memory");
+		close(io->fd);
+		unlink(path);
+		return -1;
+	}
+	io__init(io, io->fd, io->buf, buf_size);
+	return 0;
+}
+
+static void cleanup_test(char path[PATH_MAX], struct io *io)
+{
+	zfree(&io->buf);
+	close(io->fd);
+	unlink(path);
+}
+
+static int do_test_get_char(const char *test_string, size_t buf_size)
+{
+	char path[PATH_MAX];
+	struct io io;
+	int ch, ret = 0;
+	size_t i;
+
+	if (setup_test(path, test_string, buf_size, &io))
+		return -1;
+
+	for (i = 0; i < strlen(test_string); i++) {
+		ch = io__get_char(&io);
+
+		EXPECT_EQUAL(ch, test_string[i]);
+		EXPECT_EQUAL(io.eof, false);
+	}
+	ch = io__get_char(&io);
+	EXPECT_EQUAL(ch, -1);
+	EXPECT_EQUAL(io.eof, true);
+
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test_get_char(void)
+{
+	int i, ret = 0;
+	size_t j;
+
+	static const char *const test_strings[] = {
+		"12345678abcdef90",
+		"a\nb\nc\nd\n",
+		"\a\b\t\v\f\r",
+	};
+	for (i = 0; i <= 10; i++) {
+		for (j = 0; j < ARRAY_SIZE(test_strings); j++) {
+			if (do_test_get_char(test_strings[j], 1 << i))
+				ret = -1;
+		}
+	}
+	return ret;
+}
+
+static int do_test_get_hex(const char *test_string,
+			__u64 val1, int ch1,
+			__u64 val2, int ch2,
+			__u64 val3, int ch3,
+			bool end_eof)
+{
+	char path[PATH_MAX];
+	struct io io;
+	int ch, ret = 0;
+	__u64 hex;
+
+	if (setup_test(path, test_string, 4, &io))
+		return -1;
+
+	ch = io__get_hex(&io, &hex);
+	EXPECT_EQUAL64(hex, val1);
+	EXPECT_EQUAL(ch, ch1);
+
+	ch = io__get_hex(&io, &hex);
+	EXPECT_EQUAL64(hex, val2);
+	EXPECT_EQUAL(ch, ch2);
+
+	ch = io__get_hex(&io, &hex);
+	EXPECT_EQUAL64(hex, val3);
+	EXPECT_EQUAL(ch, ch3);
+
+	EXPECT_EQUAL(io.eof, end_eof);
+
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test_get_hex(void)
+{
+	int ret = 0;
+
+	if (do_test_get_hex("12345678abcdef90",
+				0x12345678abcdef90, -1,
+				0, -1,
+				0, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_hex("1\n2\n3\n",
+				1, '\n',
+				2, '\n',
+				3, '\n',
+				false))
+		ret = -1;
+
+	if (do_test_get_hex("12345678ABCDEF90;a;b",
+				0x12345678abcdef90, ';',
+				0xa, ';',
+				0xb, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_hex("0x1x2x",
+				0, 'x',
+				1, 'x',
+				2, 'x',
+				false))
+		ret = -1;
+
+	if (do_test_get_hex("x1x",
+				0, -2,
+				1, 'x',
+				0, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_hex("10000000000000000000000000000abcdefgh99i",
+				0xabcdef, 'g',
+				0, -2,
+				0x99, 'i',
+				false))
+		ret = -1;
+
+	return ret;
+}
+
+static int do_test_get_dec(const char *test_string,
+			__u64 val1, int ch1,
+			__u64 val2, int ch2,
+			__u64 val3, int ch3,
+			bool end_eof)
+{
+	char path[PATH_MAX];
+	struct io io;
+	int ch, ret = 0;
+	__u64 dec;
+
+	if (setup_test(path, test_string, 4, &io))
+		return -1;
+
+	ch = io__get_dec(&io, &dec);
+	EXPECT_EQUAL64(dec, val1);
+	EXPECT_EQUAL(ch, ch1);
+
+	ch = io__get_dec(&io, &dec);
+	EXPECT_EQUAL64(dec, val2);
+	EXPECT_EQUAL(ch, ch2);
+
+	ch = io__get_dec(&io, &dec);
+	EXPECT_EQUAL64(dec, val3);
+	EXPECT_EQUAL(ch, ch3);
+
+	EXPECT_EQUAL(io.eof, end_eof);
+
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test_get_dec(void)
+{
+	int ret = 0;
+
+	if (do_test_get_dec("12345678abcdef90",
+				12345678, 'a',
+				0, -2,
+				0, -2,
+				false))
+		ret = -1;
+
+	if (do_test_get_dec("1\n2\n3\n",
+				1, '\n',
+				2, '\n',
+				3, '\n',
+				false))
+		ret = -1;
+
+	if (do_test_get_dec("12345678;1;2",
+				12345678, ';',
+				1, ';',
+				2, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_dec("0x1x2x",
+				0, 'x',
+				1, 'x',
+				2, 'x',
+				false))
+		ret = -1;
+
+	if (do_test_get_dec("x1x",
+				0, -2,
+				1, 'x',
+				0, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_dec("10000000000000000000000000000000000000000000000000000000000123456789ab99c",
+				123456789, 'a',
+				0, -2,
+				99, 'c',
+				false))
+		ret = -1;
+
+	return ret;
+}
+
+static int test_get_line(void)
+{
+	char path[PATH_MAX];
+	struct io io;
+	char test_string[1024];
+	char *line = NULL;
+	size_t i, line_len = 0;
+	size_t buf_size = 128;
+	int ret = 0;
+
+	for (i = 0; i < 512; i++)
+		test_string[i] = 'a';
+	test_string[512] = '\n';
+	for (i = 513; i < 1023; i++)
+		test_string[i] = 'b';
+	test_string[1023] = '\0';
+
+	if (setup_test(path, test_string, buf_size, &io))
+		return -1;
+
+	EXPECT_EQUAL((int)io__getline(&io, &line, &line_len), 513);
+	EXPECT_EQUAL((int)strlen(line), 513);
+	for (i = 0; i < 512; i++)
+		EXPECT_EQUAL(line[i], 'a');
+	EXPECT_EQUAL(line[512], '\n');
+	EXPECT_EQUAL((int)io__getline(&io, &line, &line_len), 510);
+	for (i = 0; i < 510; i++)
+		EXPECT_EQUAL(line[i], 'b');
+
+	free(line);
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test__api_io(struct test_suite *test __maybe_unused,
+			int subtest __maybe_unused)
+{
+	int ret = 0;
+
+	if (test_get_char())
+		ret = TEST_FAIL;
+	if (test_get_hex())
+		ret = TEST_FAIL;
+	if (test_get_dec())
+		ret = TEST_FAIL;
+	if (test_get_line())
+		ret = TEST_FAIL;
+	return ret;
+}
+
+DEFINE_SUITE("Test api io", api_io);