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/io_uring/fs.c b/io_uring/fs.c
new file mode 100644
index 000000000..26ea841a2
--- /dev/null
+++ b/io_uring/fs.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/namei.h>
+#include <linux/io_uring.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "../fs/internal.h"
+
+#include "io_uring.h"
+#include "fs.h"
+
+struct io_rename {
+	struct file			*file;
+	int				old_dfd;
+	int				new_dfd;
+	struct delayed_filename		oldpath;
+	struct delayed_filename		newpath;
+	int				flags;
+};
+
+struct io_unlink {
+	struct file			*file;
+	int				dfd;
+	int				flags;
+	struct delayed_filename		filename;
+};
+
+struct io_mkdir {
+	struct file			*file;
+	int				dfd;
+	umode_t				mode;
+	struct delayed_filename		filename;
+};
+
+struct io_link {
+	struct file			*file;
+	int				old_dfd;
+	int				new_dfd;
+	struct delayed_filename		oldpath;
+	struct delayed_filename		newpath;
+	int				flags;
+};
+
+int io_renameat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_rename *ren = io_kiocb_to_cmd(req, struct io_rename);
+	const char __user *oldf, *newf;
+	int err;
+
+	if (sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	ren->old_dfd = READ_ONCE(sqe->fd);
+	oldf = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	newf = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+	ren->new_dfd = READ_ONCE(sqe->len);
+	ren->flags = READ_ONCE(sqe->rename_flags);
+
+	err = delayed_getname(&ren->oldpath, oldf);
+	if (unlikely(err))
+		return err;
+
+	err = delayed_getname(&ren->newpath, newf);
+	if (unlikely(err)) {
+		dismiss_delayed_filename(&ren->oldpath);
+		return err;
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_renameat(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_rename *ren = io_kiocb_to_cmd(req, struct io_rename);
+	CLASS(filename_complete_delayed, old)(&ren->oldpath);
+	CLASS(filename_complete_delayed, new)(&ren->newpath);
+	int ret;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	ret = filename_renameat2(ren->old_dfd, old,
+				 ren->new_dfd, new, ren->flags);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+void io_renameat_cleanup(struct io_kiocb *req)
+{
+	struct io_rename *ren = io_kiocb_to_cmd(req, struct io_rename);
+
+	dismiss_delayed_filename(&ren->oldpath);
+	dismiss_delayed_filename(&ren->newpath);
+}
+
+int io_unlinkat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_unlink *un = io_kiocb_to_cmd(req, struct io_unlink);
+	const char __user *fname;
+	int err;
+
+	if (sqe->off || sqe->len || sqe->buf_index || sqe->splice_fd_in ||
+	    sqe->addr3 || sqe->__pad2[0])
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	un->dfd = READ_ONCE(sqe->fd);
+
+	un->flags = READ_ONCE(sqe->unlink_flags);
+	if (un->flags & ~AT_REMOVEDIR)
+		return -EINVAL;
+
+	fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	err = delayed_getname(&un->filename, fname);
+	if (unlikely(err))
+		return err;
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_unlinkat(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_unlink *un = io_kiocb_to_cmd(req, struct io_unlink);
+	CLASS(filename_complete_delayed, name)(&un->filename);
+	int ret;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	if (un->flags & AT_REMOVEDIR)
+		ret = filename_rmdir(un->dfd, name);
+	else
+		ret = filename_unlinkat(un->dfd, name);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+void io_unlinkat_cleanup(struct io_kiocb *req)
+{
+	struct io_unlink *ul = io_kiocb_to_cmd(req, struct io_unlink);
+
+	dismiss_delayed_filename(&ul->filename);
+}
+
+int io_mkdirat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_mkdir *mkd = io_kiocb_to_cmd(req, struct io_mkdir);
+	const char __user *fname;
+	int err;
+
+	if (sqe->off || sqe->rw_flags || sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	mkd->dfd = READ_ONCE(sqe->fd);
+	mkd->mode = READ_ONCE(sqe->len);
+
+	fname = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	err = delayed_getname(&mkd->filename, fname);
+	if (unlikely(err))
+		return err;
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_mkdirat(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_mkdir *mkd = io_kiocb_to_cmd(req, struct io_mkdir);
+	CLASS(filename_complete_delayed, name)(&mkd->filename);
+	int ret;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	ret = filename_mkdirat(mkd->dfd, name, mkd->mode);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+void io_mkdirat_cleanup(struct io_kiocb *req)
+{
+	struct io_mkdir *md = io_kiocb_to_cmd(req, struct io_mkdir);
+
+	dismiss_delayed_filename(&md->filename);
+}
+
+int io_symlinkat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_link *sl = io_kiocb_to_cmd(req, struct io_link);
+	const char __user *oldpath, *newpath;
+	int err;
+
+	if (sqe->len || sqe->rw_flags || sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	sl->new_dfd = READ_ONCE(sqe->fd);
+	oldpath = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	newpath = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+
+	err = delayed_getname(&sl->oldpath, oldpath);
+	if (unlikely(err))
+		return err;
+
+	err = delayed_getname(&sl->newpath, newpath);
+	if (unlikely(err)) {
+		dismiss_delayed_filename(&sl->oldpath);
+		return err;
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_symlinkat(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_link *sl = io_kiocb_to_cmd(req, struct io_link);
+	CLASS(filename_complete_delayed, old)(&sl->oldpath);
+	CLASS(filename_complete_delayed, new)(&sl->newpath);
+	int ret;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	ret = filename_symlinkat(old, sl->new_dfd, new);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+int io_linkat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_link *lnk = io_kiocb_to_cmd(req, struct io_link);
+	const char __user *oldf, *newf;
+	int err;
+
+	if (sqe->buf_index || sqe->splice_fd_in)
+		return -EINVAL;
+	if (unlikely(req->flags & REQ_F_FIXED_FILE))
+		return -EBADF;
+
+	lnk->old_dfd = READ_ONCE(sqe->fd);
+	lnk->new_dfd = READ_ONCE(sqe->len);
+	oldf = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	newf = u64_to_user_ptr(READ_ONCE(sqe->addr2));
+	lnk->flags = READ_ONCE(sqe->hardlink_flags);
+
+	err = delayed_getname_uflags(&lnk->oldpath, oldf, lnk->flags);
+	if (unlikely(err))
+		return err;
+
+	err = delayed_getname(&lnk->newpath, newf);
+	if (unlikely(err)) {
+		dismiss_delayed_filename(&lnk->oldpath);
+		return err;
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
+	req->flags |= REQ_F_FORCE_ASYNC;
+	return 0;
+}
+
+int io_linkat(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_link *lnk = io_kiocb_to_cmd(req, struct io_link);
+	CLASS(filename_complete_delayed, old)(&lnk->oldpath);
+	CLASS(filename_complete_delayed, new)(&lnk->newpath);
+	int ret;
+
+	WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+	ret = filename_linkat(lnk->old_dfd, old, lnk->new_dfd, new, lnk->flags);
+
+	req->flags &= ~REQ_F_NEED_CLEANUP;
+	io_req_set_res(req, ret, 0);
+	return IOU_COMPLETE;
+}
+
+void io_link_cleanup(struct io_kiocb *req)
+{
+	struct io_link *sl = io_kiocb_to_cmd(req, struct io_link);
+
+	dismiss_delayed_filename(&sl->oldpath);
+	dismiss_delayed_filename(&sl->newpath);
+}