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, 306 insertions, 0 deletions

diff --git a/tools/perf/tests/tests-scripts.c b/tools/perf/tests/tests-scripts.c
new file mode 100644
index 000000000..0370bc701
--- /dev/null
+++ b/tools/perf/tests/tests-scripts.c
@@ -0,0 +1,306 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/ctype.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/zalloc.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <subcmd/exec-cmd.h>
+#include <subcmd/parse-options.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <api/io.h>
+#include "builtin.h"
+#include "tests-scripts.h"
+#include "color.h"
+#include "debug.h"
+#include "hist.h"
+#include "intlist.h"
+#include "string2.h"
+#include "symbol.h"
+#include "tests.h"
+#include "util/rlimit.h"
+#include "util/util.h"
+
+static int shell_tests__dir_fd(void)
+{
+	struct stat st;
+	char path[PATH_MAX], path2[PATH_MAX], *exec_path;
+	ssize_t len;
+	static const char * const devel_dirs[] = {
+		"./tools/perf/tests/shell",
+		"./tests/shell",
+		"./source/tests/shell"
+	};
+	int fd;
+	char *p;
+
+	for (size_t i = 0; i < ARRAY_SIZE(devel_dirs); ++i) {
+		fd = open(devel_dirs[i], O_PATH);
+
+		if (fd >= 0)
+			return fd;
+	}
+
+	/* Use directory of executable */
+	len = readlink("/proc/self/exe", path2, sizeof(path2) - 1);
+	if (len < 0)
+		return -1;
+	path2[len] = '\0';
+	/* Follow another level of symlink if there */
+	if (lstat(path2, &st) == 0 && (st.st_mode & S_IFMT) == S_IFLNK) {
+		scnprintf(path, sizeof(path), "%s", path2);
+		len = readlink(path, path2, sizeof(path2) - 1);
+		if (len < 0)
+			return -1;
+		path2[len] = '\0';
+	}
+	/* Get directory */
+	p = strrchr(path2, '/');
+	if (p)
+		*p = 0;
+	scnprintf(path, sizeof(path), "%s/tests/shell", path2);
+	fd = open(path, O_PATH);
+	if (fd >= 0)
+		return fd;
+	scnprintf(path, sizeof(path), "%s/source/tests/shell", path2);
+	fd = open(path, O_PATH);
+	if (fd >= 0)
+		return fd;
+
+	/* Then installed path. */
+	exec_path = get_argv_exec_path();
+	scnprintf(path, sizeof(path), "%s/tests/shell", exec_path);
+	free(exec_path);
+	return open(path, O_PATH);
+}
+
+static char *shell_test__description(int dir_fd, const char *name)
+{
+	struct io io;
+	char buf[128], *line = NULL;
+	size_t line_len = 0;
+	ssize_t len;
+	char *desc = NULL;
+	const char *spdx = "SPDX-License";
+
+	io__init(&io, openat(dir_fd, name, O_RDONLY), buf, sizeof(buf));
+	if (io.fd < 0)
+		return NULL;
+
+	while ((len = io__getline(&io, &line, &line_len)) > 0) {
+		char *p = line;
+
+		/* Skip leading whitespace */
+		while (*p && isspace(*p))
+			p++;
+
+		/* Must be a comment */
+		if (*p != '#')
+			continue;
+		p++;
+
+		/* Skip shebang or SPDX lines */
+		if (*p == '!' || (strstr(p, spdx) && strstr(p, "-Identifier:")))
+			continue;
+
+		/* Skip whitespace after # */
+		while (*p && isspace(*p))
+			p++;
+
+		/* If we found non-empty text, this is the description! */
+		if (*p && *p != '\n') {
+			char *end = p + strlen(p);
+
+			while (end > p && isspace(end[-1]))
+				end--;
+			*end = '\0';
+			desc = strdup(p);
+			break;
+		}
+	}
+	free(line);
+	close(io.fd);
+	return desc;
+}
+
+/* Is this full file path a shell script */
+static bool is_shell_script(int dir_fd, const char *path)
+{
+	const char *ext;
+
+	ext = strrchr(path, '.');
+	if (!ext)
+		return false;
+	if (!strcmp(ext, ".sh")) { /* Has .sh extension */
+		if (faccessat(dir_fd, path, R_OK | X_OK, 0) == 0) /* Is executable */
+			return true;
+	}
+	return false;
+}
+
+/* Is this file in this dir a shell script (for test purposes) */
+static bool is_test_script(int dir_fd, const char *name)
+{
+	return is_shell_script(dir_fd, name);
+}
+
+/* Duplicate a string and fall over and die if we run out of memory */
+static char *strdup_check(const char *str)
+{
+	char *newstr;
+
+	newstr = strdup(str);
+	if (!newstr) {
+		pr_err("Out of memory while duplicating test script string\n");
+		abort();
+	}
+	return newstr;
+}
+
+static int shell_test__run(struct test_suite *test, int subtest __maybe_unused)
+{
+	const char *file = test->priv;
+	int err;
+	char *cmd = NULL;
+
+	if (asprintf(&cmd, "%s%s", file, verbose ? " -v" : "") < 0)
+		return TEST_FAIL;
+	err = system(cmd);
+	free(cmd);
+	if (!err)
+		return TEST_OK;
+
+	return WEXITSTATUS(err) == 2 ? TEST_SKIP : TEST_FAIL;
+}
+
+static void append_script(int dir_fd, const char *name, char *desc,
+			  struct test_suite ***result,
+			  size_t *result_sz)
+{
+	char filename[PATH_MAX], link[128];
+	struct test_suite *test_suite, **result_tmp;
+	struct test_case *tests;
+	ssize_t len;
+	char *exclusive;
+
+	snprintf(link, sizeof(link), "/proc/%d/fd/%d", getpid(), dir_fd);
+	len = readlink(link, filename, sizeof(filename) - 1);
+	if (len < 0 || (size_t)len > sizeof(filename) - strlen(name) - 2) {
+		pr_err("Failed to readlink %s or path too long", link);
+		return;
+	}
+	filename[len++] = '/';
+	strcpy(&filename[len], name);
+
+	tests = calloc(2, sizeof(*tests));
+	if (!tests) {
+		pr_err("Out of memory while building script test suite list\n");
+		return;
+	}
+	tests[0].name = strdup_check(name);
+	exclusive = strstr(desc, " (exclusive)");
+	if (exclusive != NULL) {
+		tests[0].exclusive = true;
+		exclusive[0] = '\0';
+	}
+	tests[0].desc = strdup_check(desc);
+	tests[0].run_case = shell_test__run;
+	test_suite = zalloc(sizeof(*test_suite));
+	if (!test_suite) {
+		pr_err("Out of memory while building script test suite list\n");
+		free(tests);
+		return;
+	}
+	test_suite->desc = desc;
+	test_suite->test_cases = tests;
+	test_suite->priv = strdup_check(filename);
+	/* Realloc is good enough, though we could realloc by chunks, not that
+	 * anyone will ever measure performance here */
+	result_tmp = realloc(*result, (*result_sz + 1) * sizeof(*result_tmp));
+	if (result_tmp == NULL) {
+		pr_err("Out of memory while building script test suite list\n");
+		free(tests);
+		free(test_suite);
+		return;
+	}
+	/* Add file to end and NULL terminate the struct array */
+	*result = result_tmp;
+	(*result)[*result_sz] = test_suite;
+	(*result_sz)++;
+}
+
+static void append_scripts_in_dir(int dir_fd,
+				  struct test_suite ***result,
+				  size_t *result_sz)
+{
+	struct dirent **entlist;
+	struct dirent *ent;
+	int n_dirs, i;
+
+	/* List files, sorted by alpha */
+	n_dirs = scandirat(dir_fd, ".", &entlist, NULL, alphasort);
+	if (n_dirs == -1)
+		return;
+	for (i = 0; i < n_dirs && (ent = entlist[i]); i++) {
+		int fd;
+
+		if (ent->d_name[0] == '.')
+			continue; /* Skip hidden files */
+		if (is_test_script(dir_fd, ent->d_name)) { /* It's a test */
+			char *desc = shell_test__description(dir_fd, ent->d_name);
+
+			if (desc) /* It has a desc line - valid script */
+				append_script(dir_fd, ent->d_name, desc, result, result_sz);
+			continue;
+		}
+		if (ent->d_type != DT_DIR) {
+			struct stat st;
+
+			if (ent->d_type != DT_UNKNOWN)
+				continue;
+			fstatat(dir_fd, ent->d_name, &st, 0);
+			if (!S_ISDIR(st.st_mode))
+				continue;
+		}
+		if (strncmp(ent->d_name, "base_", 5) == 0)
+			continue; /* Skip scripts that have a separate driver. */
+		fd = openat(dir_fd, ent->d_name, O_PATH);
+		append_scripts_in_dir(fd, result, result_sz);
+		close(fd);
+	}
+	for (i = 0; i < n_dirs; i++) /* Clean up */
+		zfree(&entlist[i]);
+	free(entlist);
+}
+
+struct test_suite **create_script_test_suites(void)
+{
+	struct test_suite **result = NULL, **result_tmp;
+	size_t result_sz = 0;
+	int dir_fd = shell_tests__dir_fd(); /* Walk  dir */
+
+	/*
+	 * Append scripts if fd is good, otherwise return a NULL terminated zero
+	 * length array.
+	 */
+	if (dir_fd >= 0)
+		append_scripts_in_dir(dir_fd, &result, &result_sz);
+
+	result_tmp = realloc(result, (result_sz + 1) * sizeof(*result_tmp));
+	if (result_tmp == NULL) {
+		pr_err("Out of memory while building script test suite list\n");
+		abort();
+	}
+	/* NULL terminate the test suite array. */
+	result = result_tmp;
+	result[result_sz] = NULL;
+	if (dir_fd >= 0)
+		close(dir_fd);
+	return result;
+}