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, 580 insertions, 0 deletions

diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
new file mode 100644
index 000000000..94dc534a7
--- /dev/null
+++ b/tools/perf/util/data.c
@@ -0,0 +1,580 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/zalloc.h>
+#include <linux/err.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <asm/bug.h>
+#include <dirent.h>
+
+#include "data.h"
+#include "util.h" // rm_rf_perf_data()
+#include "debug.h"
+#include "header.h"
+#include "rlimit.h"
+#include <internal/lib.h>
+
+static void perf_data_file__close(struct perf_data_file *file)
+{
+	if (file->use_stdio) {
+		if (file->fptr) {
+			fclose(file->fptr);
+			file->fptr = NULL;
+		}
+	} else {
+		close(file->fd);
+		file->fd = -1;
+	}
+	zfree(&file->path);
+}
+
+static void close_dir(struct perf_data_file *files, int nr)
+{
+	while (--nr >= 0)
+		perf_data_file__close(&files[nr]);
+
+	free(files);
+}
+
+void perf_data__close_dir(struct perf_data *data)
+{
+	close_dir(data->dir.files, data->dir.nr);
+	data->dir.files = NULL;
+	data->dir.nr = 0;
+}
+
+int perf_data__create_dir(struct perf_data *data, int nr)
+{
+	enum rlimit_action set_rlimit = NO_CHANGE;
+	struct perf_data_file *files = NULL;
+	int i, ret;
+
+	if (WARN_ON(!data->is_dir))
+		return -EINVAL;
+
+	files = calloc(nr, sizeof(*files));
+	if (!files)
+		return -ENOMEM;
+
+	for (i = 0; i < nr; i++) {
+		struct perf_data_file *file = &files[i];
+
+		ret = asprintf(&file->path, "%s/data.%d", data->path, i);
+		if (ret < 0) {
+			ret = -ENOMEM;
+			goto out_err;
+		}
+
+retry_open:
+		ret = open(file->path, O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR);
+		if (ret < 0) {
+			/*
+			 * If using parallel threads to collect data,
+			 * perf record needs at least 6 fds per CPU.
+			 * When we run out of them try to increase the limits.
+			 */
+			if (errno == EMFILE && rlimit__increase_nofile(&set_rlimit))
+				goto retry_open;
+
+			ret = -errno;
+			goto out_err;
+		}
+		set_rlimit = NO_CHANGE;
+
+		file->fd = ret;
+	}
+
+	data->dir.version = PERF_DIR_VERSION;
+	data->dir.files   = files;
+	data->dir.nr      = nr;
+	return 0;
+
+out_err:
+	close_dir(files, i);
+	return ret;
+}
+
+int perf_data__open_dir(struct perf_data *data)
+{
+	struct perf_data_file *files = NULL;
+	struct dirent *dent;
+	int ret = -1;
+	DIR *dir;
+	int nr = 0;
+
+	/*
+	 * Directory containing a single regular perf data file which is already
+	 * open, means there is nothing more to do here.
+	 */
+	if (perf_data__is_single_file(data))
+		return 0;
+
+	if (WARN_ON(!data->is_dir))
+		return -EINVAL;
+
+	/* The version is provided by DIR_FORMAT feature. */
+	if (WARN_ON(data->dir.version != PERF_DIR_VERSION))
+		return -1;
+
+	dir = opendir(data->path);
+	if (!dir)
+		return -EINVAL;
+
+	while ((dent = readdir(dir)) != NULL) {
+		struct perf_data_file *file;
+		char path[PATH_MAX];
+		struct stat st;
+
+		snprintf(path, sizeof(path), "%s/%s", data->path, dent->d_name);
+		if (stat(path, &st))
+			continue;
+
+		if (!S_ISREG(st.st_mode) || strncmp(dent->d_name, "data.", 5))
+			continue;
+
+		ret = -ENOMEM;
+
+		file = realloc(files, (nr + 1) * sizeof(*files));
+		if (!file)
+			goto out_err;
+
+		files = file;
+		file = &files[nr++];
+
+		*file = (struct perf_data_file){
+			.path = strdup(path),
+			.fd = -1,
+			.size = st.st_size,
+			.use_stdio = false,
+		};
+		if (!file->path)
+			goto out_err;
+
+		ret = open(file->path, O_RDONLY);
+		if (ret < 0) {
+			ret = -errno;
+			goto out_err;
+		}
+		file->fd = ret;
+	}
+
+	closedir(dir);
+	if (!files)
+		return -EINVAL;
+
+	data->dir.files = files;
+	data->dir.nr    = nr;
+	return 0;
+
+out_err:
+	closedir(dir);
+	close_dir(files, nr);
+	return ret;
+}
+
+static bool check_pipe(struct perf_data *data)
+{
+	struct stat st;
+	bool is_pipe = false;
+	int fd = perf_data__is_read(data) ?
+		 STDIN_FILENO : STDOUT_FILENO;
+
+	if (!data->path) {
+		if (!fstat(fd, &st) && S_ISFIFO(st.st_mode))
+			is_pipe = true;
+	} else {
+		if (!strcmp(data->path, "-"))
+			is_pipe = true;
+	}
+
+	if (is_pipe) {
+		if (data->file.use_stdio) {
+			const char *mode;
+
+			mode = perf_data__is_read(data) ? "r" : "w";
+			data->file.fptr = fdopen(fd, mode);
+
+			if (data->file.fptr == NULL) {
+				data->file.fd = fd;
+				data->file.use_stdio = false;
+			}
+
+		/*
+		 * When is_pipe and data->file.fd is given, use given fd
+		 * instead of STDIN_FILENO or STDOUT_FILENO
+		 */
+		} else if (data->file.fd <= 0) {
+			data->file.fd = fd;
+		}
+	}
+
+	return data->is_pipe = is_pipe;
+}
+
+static int check_backup(struct perf_data *data)
+{
+	struct stat st;
+
+	if (perf_data__is_read(data))
+		return 0;
+
+	if (!stat(data->path, &st) && st.st_size) {
+		char oldname[PATH_MAX];
+		int ret;
+
+		snprintf(oldname, sizeof(oldname), "%s.old",
+			 data->path);
+
+		ret = rm_rf_perf_data(oldname);
+		if (ret) {
+			if (ret == -2)
+				pr_err("Can't remove old data: Unknown file found (%s)\n", oldname);
+			else
+				pr_err("Can't remove old data: %m (%s)\n", oldname);
+			return -1;
+		}
+
+		if (rename(data->path, oldname)) {
+			pr_err("Can't move data: %m (%s to %s)\n", data->path, oldname);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+static bool is_dir(struct perf_data *data)
+{
+	struct stat st;
+
+	if (stat(data->path, &st))
+		return false;
+
+	return (st.st_mode & S_IFMT) == S_IFDIR;
+}
+
+static int open_file_read(struct perf_data *data)
+{
+	int flags = data->in_place_update ? O_RDWR : O_RDONLY;
+	struct stat st;
+	int fd;
+
+	fd = open(data->file.path, flags);
+	if (fd < 0) {
+		int err = errno;
+
+		pr_err("failed to open %s: %m", data->file.path);
+		if (err == ENOENT && !strcmp(data->file.path, "perf.data"))
+			pr_err("  (try 'perf record' first)");
+		pr_err("\n");
+		return -err;
+	}
+
+	if (fstat(fd, &st) < 0)
+		goto out_close;
+
+	if (!data->force && st.st_uid && (st.st_uid != geteuid())) {
+		pr_err("File %s not owned by current user or root (use -f to override)\n",
+		       data->file.path);
+		goto out_close;
+	}
+
+	if (!st.st_size) {
+		pr_info("zero-sized data (%s), nothing to do!\n",
+			data->file.path);
+		goto out_close;
+	}
+
+	data->file.size = st.st_size;
+	return fd;
+
+ out_close:
+	close(fd);
+	return -1;
+}
+
+static int open_file_write(struct perf_data *data)
+{
+	int fd = open(data->file.path, O_CREAT|O_RDWR|O_TRUNC|O_CLOEXEC, S_IRUSR|S_IWUSR);
+
+	if (fd < 0)
+		pr_err("failed to open %s : %m\n", data->file.path);
+
+	return fd;
+}
+
+static int open_file(struct perf_data *data)
+{
+	int fd;
+
+	fd = perf_data__is_read(data) ?
+	     open_file_read(data) : open_file_write(data);
+
+	if (fd < 0) {
+		zfree(&data->file.path);
+		return -1;
+	}
+
+	data->file.fd = fd;
+	return 0;
+}
+
+static int open_file_dup(struct perf_data *data)
+{
+	data->file.path = strdup(data->path);
+	if (!data->file.path)
+		return -ENOMEM;
+
+	return open_file(data);
+}
+
+static int open_dir(struct perf_data *data)
+{
+	int ret;
+
+	/*
+	 * So far we open only the header, so we can read the data version and
+	 * layout.
+	 */
+	if (asprintf(&data->file.path, "%s/data", data->path) < 0)
+		return -1;
+
+	if (perf_data__is_write(data) &&
+	    mkdir(data->path, S_IRWXU) < 0)
+		return -1;
+
+	ret = open_file(data);
+
+	/* Cleanup whatever we managed to create so far. */
+	if (ret && perf_data__is_write(data))
+		rm_rf_perf_data(data->path);
+
+	return ret;
+}
+
+int perf_data__open(struct perf_data *data)
+{
+	if (check_pipe(data))
+		return 0;
+
+	/* currently it allows stdio for pipe only */
+	data->file.use_stdio = false;
+
+	if (!data->path)
+		data->path = "perf.data";
+
+	if (check_backup(data))
+		return -1;
+
+	if (perf_data__is_read(data))
+		data->is_dir = is_dir(data);
+
+	return perf_data__is_dir(data) ?
+	       open_dir(data) : open_file_dup(data);
+}
+
+void perf_data__close(struct perf_data *data)
+{
+	if (perf_data__is_dir(data))
+		perf_data__close_dir(data);
+
+	perf_data_file__close(&data->file);
+}
+
+static ssize_t perf_data_file__read(struct perf_data_file *file, void *buf, size_t size)
+{
+	if (file->use_stdio) {
+		if (fread(buf, size, 1, file->fptr) == 1)
+			return size;
+		return feof(file->fptr) ? 0 : -1;
+	}
+	return readn(file->fd, buf, size);
+}
+
+ssize_t perf_data__read(struct perf_data *data, void *buf, size_t size)
+{
+	return perf_data_file__read(&data->file, buf, size);
+}
+
+ssize_t perf_data_file__write(struct perf_data_file *file,
+			      void *buf, size_t size)
+{
+	if (file->use_stdio) {
+		if (fwrite(buf, size, /*nmemb=*/1, file->fptr) == 1)
+			return size;
+		return -1;
+	}
+	return writen(file->fd, buf, size);
+}
+
+ssize_t perf_data__write(struct perf_data *data,
+			 void *buf, size_t size)
+{
+	return perf_data_file__write(&data->file, buf, size);
+}
+
+off_t perf_data_file__seek(struct perf_data_file *file, off_t offset, int whence)
+{
+	if (file->use_stdio) {
+		off_t res = fseeko(file->fptr, offset, whence);
+
+		return res < 0 ? -1 : ftello(file->fptr);
+	}
+	return lseek(file->fd, offset, whence);
+}
+
+off_t perf_data__seek(struct perf_data *data, off_t offset, int whence)
+{
+	/* Note, a pipe fd will fail with -1 with errno of ESPIPE. */
+	return perf_data_file__seek(&data->file, offset, whence);
+}
+
+int perf_data__switch(struct perf_data *data,
+		      const char *postfix,
+		      size_t pos, bool at_exit,
+		      char **new_filepath)
+{
+	int ret;
+
+	if (perf_data__is_read(data))
+		return -EINVAL;
+
+	if (asprintf(new_filepath, "%s.%s", data->path, postfix) < 0)
+		return -ENOMEM;
+
+	/*
+	 * Only fire a warning, don't return error, continue fill
+	 * original file.
+	 */
+	if (rename(data->path, *new_filepath))
+		pr_warning("Failed to rename %s to %s\n", data->path, *new_filepath);
+
+	if (!at_exit) {
+		perf_data_file__close(&data->file);
+		ret = perf_data__open(data);
+		if (ret < 0)
+			goto out;
+
+		if (perf_data__seek(data, pos, SEEK_SET) == (off_t)-1) {
+			ret = -errno;
+			pr_debug("Failed to seek to %zu: %m", pos);
+			goto out;
+		}
+	}
+	ret = perf_data__fd(data);
+out:
+	return ret;
+}
+
+unsigned long perf_data__size(struct perf_data *data)
+{
+	u64 size = data->file.size;
+	int i;
+
+	if (perf_data__is_single_file(data))
+		return size;
+
+	for (i = 0; i < data->dir.nr; i++) {
+		struct perf_data_file *file = &data->dir.files[i];
+
+		size += file->size;
+	}
+
+	return size;
+}
+
+int perf_data__make_kcore_dir(struct perf_data *data, char *buf, size_t buf_sz)
+{
+	int ret;
+
+	if (!data->is_dir)
+		return -1;
+
+	ret = snprintf(buf, buf_sz, "%s/kcore_dir", data->path);
+	if (ret < 0 || (size_t)ret >= buf_sz)
+		return -1;
+
+	return mkdir(buf, S_IRWXU);
+}
+
+bool has_kcore_dir(const char *path)
+{
+	struct dirent *d = ERR_PTR(-EINVAL);
+	const char *name = "kcore_dir";
+	DIR *dir = opendir(path);
+	size_t n = strlen(name);
+	bool result = false;
+
+	if (dir) {
+		while (d && !result) {
+			d = readdir(dir);
+			result = d ? strncmp(d->d_name, name, n) : false;
+		}
+		closedir(dir);
+	}
+
+	return result;
+}
+
+char *perf_data__kallsyms_name(struct perf_data *data)
+{
+	char *kallsyms_name;
+	struct stat st;
+
+	if (!data->is_dir)
+		return NULL;
+
+	if (asprintf(&kallsyms_name, "%s/kcore_dir/kallsyms", data->path) < 0)
+		return NULL;
+
+	if (stat(kallsyms_name, &st)) {
+		free(kallsyms_name);
+		return NULL;
+	}
+
+	return kallsyms_name;
+}
+
+char *perf_data__guest_kallsyms_name(struct perf_data *data, pid_t machine_pid)
+{
+	char *kallsyms_name;
+	struct stat st;
+
+	if (!data->is_dir)
+		return NULL;
+
+	if (asprintf(&kallsyms_name, "%s/kcore_dir__%d/kallsyms", data->path, machine_pid) < 0)
+		return NULL;
+
+	if (stat(kallsyms_name, &st)) {
+		free(kallsyms_name);
+		return NULL;
+	}
+
+	return kallsyms_name;
+}
+
+bool is_perf_data(const char *path)
+{
+	bool ret = false;
+	FILE *file;
+	u64 magic;
+
+	file = fopen(path, "r");
+	if (!file)
+		return false;
+
+	if (fread(&magic, 1, 8, file) < 8)
+		goto out;
+
+	ret = is_perf_magic(magic);
+out:
+	fclose(file);
+	return ret;
+}