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, 421 insertions, 0 deletions

diff --git a/fs/hostfs/hostfs_user.c b/fs/hostfs/hostfs_user.c
new file mode 100644
index 000000000..3bcd9f35e
--- /dev/null
+++ b/fs/hostfs/hostfs_user.c
@@ -0,0 +1,421 @@
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Licensed under the GPL
+ */
+
+#include <stdio.h>
+#include <stddef.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/vfs.h>
+#include <sys/syscall.h>
+#include "hostfs.h"
+#include <utime.h>
+
+static void statx_to_hostfs(const struct statx *buf, struct hostfs_stat *p)
+{
+	p->ino = buf->stx_ino;
+	p->mode = buf->stx_mode;
+	p->nlink = buf->stx_nlink;
+	p->uid = buf->stx_uid;
+	p->gid = buf->stx_gid;
+	p->size = buf->stx_size;
+	p->atime.tv_sec = buf->stx_atime.tv_sec;
+	p->atime.tv_nsec = buf->stx_atime.tv_nsec;
+	p->ctime.tv_sec = buf->stx_ctime.tv_sec;
+	p->ctime.tv_nsec = buf->stx_ctime.tv_nsec;
+	p->mtime.tv_sec = buf->stx_mtime.tv_sec;
+	p->mtime.tv_nsec = buf->stx_mtime.tv_nsec;
+	if (buf->stx_mask & STATX_BTIME) {
+		p->btime.tv_sec = buf->stx_btime.tv_sec;
+		p->btime.tv_nsec = buf->stx_btime.tv_nsec;
+	} else {
+		memset(&p->btime, 0, sizeof(p->btime));
+	}
+	p->blksize = buf->stx_blksize;
+	p->blocks = buf->stx_blocks;
+	p->rdev.maj = buf->stx_rdev_major;
+	p->rdev.min = buf->stx_rdev_minor;
+	p->dev.maj = buf->stx_dev_major;
+	p->dev.min = buf->stx_dev_minor;
+}
+
+int stat_file(const char *path, struct hostfs_stat *p, int fd)
+{
+	struct statx buf;
+	int flags = AT_SYMLINK_NOFOLLOW;
+
+	if (fd >= 0) {
+		flags |= AT_EMPTY_PATH;
+		path = "";
+	}
+
+	if ((statx(fd, path, flags, STATX_BASIC_STATS | STATX_BTIME, &buf)) < 0)
+		return -errno;
+
+	statx_to_hostfs(&buf, p);
+	return 0;
+}
+
+int access_file(char *path, int r, int w, int x)
+{
+	int mode = 0;
+
+	if (r)
+		mode = R_OK;
+	if (w)
+		mode |= W_OK;
+	if (x)
+		mode |= X_OK;
+	if (access(path, mode) != 0)
+		return -errno;
+	else return 0;
+}
+
+int open_file(char *path, int r, int w, int append)
+{
+	int mode = 0, fd;
+
+	if (r && !w)
+		mode = O_RDONLY;
+	else if (!r && w)
+		mode = O_WRONLY;
+	else if (r && w)
+		mode = O_RDWR;
+	else panic("Impossible mode in open_file");
+
+	if (append)
+		mode |= O_APPEND;
+	fd = open64(path, mode);
+	if (fd < 0)
+		return -errno;
+	else return fd;
+}
+
+void *open_dir(char *path, int *err_out)
+{
+	DIR *dir;
+
+	dir = opendir(path);
+	*err_out = errno;
+
+	return dir;
+}
+
+void seek_dir(void *stream, unsigned long long pos)
+{
+	DIR *dir = stream;
+
+	seekdir(dir, pos);
+}
+
+char *read_dir(void *stream, unsigned long long *pos_out,
+	       unsigned long long *ino_out, int *len_out,
+	       unsigned int *type_out)
+{
+	DIR *dir = stream;
+	struct dirent *ent;
+
+	ent = readdir(dir);
+	if (ent == NULL)
+		return NULL;
+	*len_out = strlen(ent->d_name);
+	*ino_out = ent->d_ino;
+	*type_out = ent->d_type;
+	*pos_out = ent->d_off;
+	return ent->d_name;
+}
+
+int read_file(int fd, unsigned long long *offset, char *buf, int len)
+{
+	int n;
+
+	n = pread64(fd, buf, len, *offset);
+	if (n < 0)
+		return -errno;
+	*offset += n;
+	return n;
+}
+
+int write_file(int fd, unsigned long long *offset, const char *buf, int len)
+{
+	int n;
+
+	n = pwrite64(fd, buf, len, *offset);
+	if (n < 0)
+		return -errno;
+	*offset += n;
+	return n;
+}
+
+int lseek_file(int fd, long long offset, int whence)
+{
+	int ret;
+
+	ret = lseek64(fd, offset, whence);
+	if (ret < 0)
+		return -errno;
+	return 0;
+}
+
+int fsync_file(int fd, int datasync)
+{
+	int ret;
+	if (datasync)
+		ret = fdatasync(fd);
+	else
+		ret = fsync(fd);
+
+	if (ret < 0)
+		return -errno;
+	return 0;
+}
+
+int replace_file(int oldfd, int fd)
+{
+	return dup2(oldfd, fd);
+}
+
+void close_file(void *stream)
+{
+	close(*((int *) stream));
+}
+
+void close_dir(void *stream)
+{
+	closedir(stream);
+}
+
+int file_create(char *name, int mode)
+{
+	int fd;
+
+	fd = open64(name, O_CREAT | O_RDWR, mode);
+	if (fd < 0)
+		return -errno;
+	return fd;
+}
+
+int set_attr(const char *file, struct hostfs_iattr *attrs, int fd)
+{
+	struct hostfs_stat st;
+	struct timeval times[2];
+	int err, ma;
+
+	if (attrs->ia_valid & HOSTFS_ATTR_MODE) {
+		if (fd >= 0) {
+			if (fchmod(fd, attrs->ia_mode) != 0)
+				return -errno;
+		} else if (chmod(file, attrs->ia_mode) != 0) {
+			return -errno;
+		}
+	}
+	if (attrs->ia_valid & HOSTFS_ATTR_UID) {
+		if (fd >= 0) {
+			if (fchown(fd, attrs->ia_uid, -1))
+				return -errno;
+		} else if (chown(file, attrs->ia_uid, -1)) {
+			return -errno;
+		}
+	}
+	if (attrs->ia_valid & HOSTFS_ATTR_GID) {
+		if (fd >= 0) {
+			if (fchown(fd, -1, attrs->ia_gid))
+				return -errno;
+		} else if (chown(file, -1, attrs->ia_gid)) {
+			return -errno;
+		}
+	}
+	if (attrs->ia_valid & HOSTFS_ATTR_SIZE) {
+		if (fd >= 0) {
+			if (ftruncate(fd, attrs->ia_size))
+				return -errno;
+		} else if (truncate(file, attrs->ia_size)) {
+			return -errno;
+		}
+	}
+
+	/*
+	 * Update accessed and/or modified time, in two parts: first set
+	 * times according to the changes to perform, and then call futimes()
+	 * or utimes() to apply them.
+	 */
+	ma = (HOSTFS_ATTR_ATIME_SET | HOSTFS_ATTR_MTIME_SET);
+	if (attrs->ia_valid & ma) {
+		err = stat_file(file, &st, fd);
+		if (err != 0)
+			return err;
+
+		times[0].tv_sec = st.atime.tv_sec;
+		times[0].tv_usec = st.atime.tv_nsec / 1000;
+		times[1].tv_sec = st.mtime.tv_sec;
+		times[1].tv_usec = st.mtime.tv_nsec / 1000;
+
+		if (attrs->ia_valid & HOSTFS_ATTR_ATIME_SET) {
+			times[0].tv_sec = attrs->ia_atime.tv_sec;
+			times[0].tv_usec = attrs->ia_atime.tv_nsec / 1000;
+		}
+		if (attrs->ia_valid & HOSTFS_ATTR_MTIME_SET) {
+			times[1].tv_sec = attrs->ia_mtime.tv_sec;
+			times[1].tv_usec = attrs->ia_mtime.tv_nsec / 1000;
+		}
+
+		if (fd >= 0) {
+			if (futimes(fd, times) != 0)
+				return -errno;
+		} else if (utimes(file, times) != 0) {
+			return -errno;
+		}
+	}
+
+	/* Note: ctime is not handled */
+	if (attrs->ia_valid & (HOSTFS_ATTR_ATIME | HOSTFS_ATTR_MTIME)) {
+		err = stat_file(file, &st, fd);
+		attrs->ia_atime = st.atime;
+		attrs->ia_mtime = st.mtime;
+		if (err != 0)
+			return err;
+	}
+	return 0;
+}
+
+int make_symlink(const char *from, const char *to)
+{
+	int err;
+
+	err = symlink(to, from);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int unlink_file(const char *file)
+{
+	int err;
+
+	err = unlink(file);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int do_mkdir(const char *file, int mode)
+{
+	int err;
+
+	err = mkdir(file, mode);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int hostfs_do_rmdir(const char *file)
+{
+	int err;
+
+	err = rmdir(file);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int do_mknod(const char *file, int mode, unsigned int major, unsigned int minor)
+{
+	int err;
+
+	err = mknod(file, mode, os_makedev(major, minor));
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int link_file(const char *to, const char *from)
+{
+	int err;
+
+	err = link(to, from);
+	if (err)
+		return -errno;
+	return 0;
+}
+
+int hostfs_do_readlink(char *file, char *buf, int size)
+{
+	int n;
+
+	n = readlink(file, buf, size);
+	if (n < 0)
+		return -errno;
+	if (n < size)
+		buf[n] = '\0';
+	return n;
+}
+
+int rename_file(char *from, char *to)
+{
+	int err;
+
+	err = rename(from, to);
+	if (err < 0)
+		return -errno;
+	return 0;
+}
+
+int rename2_file(char *from, char *to, unsigned int flags)
+{
+	int err;
+
+#ifndef SYS_renameat2
+#  ifdef __x86_64__
+#    define SYS_renameat2 316
+#  endif
+#  ifdef __i386__
+#    define SYS_renameat2 353
+#  endif
+#endif
+
+#ifdef SYS_renameat2
+	err = syscall(SYS_renameat2, AT_FDCWD, from, AT_FDCWD, to, flags);
+	if (err < 0) {
+		if (errno != ENOSYS)
+			return -errno;
+		else
+			return -EINVAL;
+	}
+	return 0;
+#else
+	return -EINVAL;
+#endif
+}
+
+int do_statfs(char *root, long *bsize_out, long long *blocks_out,
+	      long long *bfree_out, long long *bavail_out,
+	      long long *files_out, long long *ffree_out,
+	      void *fsid_out, int fsid_size, long *namelen_out)
+{
+	struct statfs64 buf;
+	int err;
+
+	err = statfs64(root, &buf);
+	if (err < 0)
+		return -errno;
+
+	*bsize_out = buf.f_bsize;
+	*blocks_out = buf.f_blocks;
+	*bfree_out = buf.f_bfree;
+	*bavail_out = buf.f_bavail;
+	*files_out = buf.f_files;
+	*ffree_out = buf.f_ffree;
+	memcpy(fsid_out, &buf.f_fsid,
+	       sizeof(buf.f_fsid) > fsid_size ? fsid_size :
+	       sizeof(buf.f_fsid));
+	*namelen_out = buf.f_namelen;
+
+	return 0;
+}