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, 331 insertions, 0 deletions

diff --git a/fs/coda/file.c b/fs/coda/file.c
new file mode 100644
index 000000000..6ca8bfcb5
--- /dev/null
+++ b/fs/coda/file.c
@@ -0,0 +1,331 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * File operations for Coda.
+ * Original version: (C) 1996 Peter Braam 
+ * Rewritten for Linux 2.1: (C) 1997 Carnegie Mellon University
+ *
+ * Carnegie Mellon encourages users of this code to contribute improvements
+ * to the Coda project. Contact Peter Braam <coda@cs.cmu.edu>.
+ */
+
+#include <linux/refcount.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/time.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include <linux/stat.h>
+#include <linux/cred.h>
+#include <linux/errno.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/uio.h>
+#include <linux/splice.h>
+
+#include <linux/coda.h>
+#include "coda_psdev.h"
+#include "coda_linux.h"
+#include "coda_int.h"
+
+struct coda_vm_ops {
+	refcount_t refcnt;
+	struct file *coda_file;
+	const struct vm_operations_struct *host_vm_ops;
+	struct vm_operations_struct vm_ops;
+};
+
+static ssize_t
+coda_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct file *coda_file = iocb->ki_filp;
+	struct inode *coda_inode = file_inode(coda_file);
+	struct coda_file_info *cfi = coda_ftoc(coda_file);
+	loff_t ki_pos = iocb->ki_pos;
+	size_t count = iov_iter_count(to);
+	ssize_t ret;
+
+	ret = venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+				  &cfi->cfi_access_intent,
+				  count, ki_pos, CODA_ACCESS_TYPE_READ);
+	if (ret)
+		goto finish_read;
+
+	ret = vfs_iter_read(cfi->cfi_container, to, &iocb->ki_pos, 0);
+
+finish_read:
+	venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+			    &cfi->cfi_access_intent,
+			    count, ki_pos, CODA_ACCESS_TYPE_READ_FINISH);
+	return ret;
+}
+
+static ssize_t
+coda_file_write_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct file *coda_file = iocb->ki_filp;
+	struct inode *coda_inode = file_inode(coda_file);
+	struct coda_file_info *cfi = coda_ftoc(coda_file);
+	struct file *host_file = cfi->cfi_container;
+	loff_t ki_pos = iocb->ki_pos;
+	size_t count = iov_iter_count(to);
+	ssize_t ret;
+
+	ret = venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+				  &cfi->cfi_access_intent,
+				  count, ki_pos, CODA_ACCESS_TYPE_WRITE);
+	if (ret)
+		goto finish_write;
+
+	inode_lock(coda_inode);
+	ret = vfs_iter_write(cfi->cfi_container, to, &iocb->ki_pos, 0);
+	coda_inode->i_size = file_inode(host_file)->i_size;
+	coda_inode->i_blocks = (coda_inode->i_size + 511) >> 9;
+	inode_set_mtime_to_ts(coda_inode, inode_set_ctime_current(coda_inode));
+	inode_unlock(coda_inode);
+
+finish_write:
+	venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+			    &cfi->cfi_access_intent,
+			    count, ki_pos, CODA_ACCESS_TYPE_WRITE_FINISH);
+	return ret;
+}
+
+static ssize_t
+coda_file_splice_read(struct file *coda_file, loff_t *ppos,
+		      struct pipe_inode_info *pipe,
+		      size_t len, unsigned int flags)
+{
+	struct inode *coda_inode = file_inode(coda_file);
+	struct coda_file_info *cfi = coda_ftoc(coda_file);
+	struct file *in = cfi->cfi_container;
+	loff_t ki_pos = *ppos;
+	ssize_t ret;
+
+	ret = venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+				  &cfi->cfi_access_intent,
+				  len, ki_pos, CODA_ACCESS_TYPE_READ);
+	if (ret)
+		goto finish_read;
+
+	ret = vfs_splice_read(in, ppos, pipe, len, flags);
+
+finish_read:
+	venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+			    &cfi->cfi_access_intent,
+			    len, ki_pos, CODA_ACCESS_TYPE_READ_FINISH);
+	return ret;
+}
+
+static void
+coda_vm_open(struct vm_area_struct *vma)
+{
+	struct coda_vm_ops *cvm_ops =
+		container_of(vma->vm_ops, struct coda_vm_ops, vm_ops);
+
+	refcount_inc(&cvm_ops->refcnt);
+
+	if (cvm_ops->host_vm_ops && cvm_ops->host_vm_ops->open)
+		cvm_ops->host_vm_ops->open(vma);
+}
+
+static void
+coda_vm_close(struct vm_area_struct *vma)
+{
+	struct coda_vm_ops *cvm_ops =
+		container_of(vma->vm_ops, struct coda_vm_ops, vm_ops);
+
+	if (cvm_ops->host_vm_ops && cvm_ops->host_vm_ops->close)
+		cvm_ops->host_vm_ops->close(vma);
+
+	if (refcount_dec_and_test(&cvm_ops->refcnt)) {
+		vma->vm_ops = cvm_ops->host_vm_ops;
+		fput(cvm_ops->coda_file);
+		kfree(cvm_ops);
+	}
+}
+
+static int
+coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
+{
+	struct inode *coda_inode = file_inode(coda_file);
+	struct coda_file_info *cfi = coda_ftoc(coda_file);
+	struct file *host_file = cfi->cfi_container;
+	struct inode *host_inode = file_inode(host_file);
+	struct coda_inode_info *cii;
+	struct coda_vm_ops *cvm_ops;
+	loff_t ppos;
+	size_t count;
+	int ret;
+
+	if (!can_mmap_file(host_file))
+		return -ENODEV;
+
+	if (WARN_ON(coda_file != vma->vm_file))
+		return -EIO;
+
+	count = vma->vm_end - vma->vm_start;
+	ppos = vma->vm_pgoff * PAGE_SIZE;
+
+	ret = venus_access_intent(coda_inode->i_sb, coda_i2f(coda_inode),
+				  &cfi->cfi_access_intent,
+				  count, ppos, CODA_ACCESS_TYPE_MMAP);
+	if (ret)
+		return ret;
+
+	cvm_ops = kmalloc_obj(struct coda_vm_ops);
+	if (!cvm_ops)
+		return -ENOMEM;
+
+	cii = ITOC(coda_inode);
+	spin_lock(&cii->c_lock);
+	coda_file->f_mapping = host_file->f_mapping;
+	if (coda_inode->i_mapping == &coda_inode->i_data)
+		coda_inode->i_mapping = host_inode->i_mapping;
+
+	/* only allow additional mmaps as long as userspace isn't changing
+	 * the container file on us! */
+	else if (coda_inode->i_mapping != host_inode->i_mapping) {
+		spin_unlock(&cii->c_lock);
+		kfree(cvm_ops);
+		return -EBUSY;
+	}
+
+	/* keep track of how often the coda_inode/host_file has been mmapped */
+	cii->c_mapcount++;
+	cfi->cfi_mapcount++;
+	spin_unlock(&cii->c_lock);
+
+	vma->vm_file = get_file(host_file);
+	ret = vfs_mmap(vma->vm_file, vma);
+
+	if (ret) {
+		/* if vfs_mmap fails, our caller will put host_file so we
+		 * should drop the reference to the coda_file that we got.
+		 */
+		fput(coda_file);
+		kfree(cvm_ops);
+	} else {
+		/* here we add redirects for the open/close vm_operations */
+		cvm_ops->host_vm_ops = vma->vm_ops;
+		if (vma->vm_ops)
+			cvm_ops->vm_ops = *vma->vm_ops;
+
+		cvm_ops->vm_ops.open = coda_vm_open;
+		cvm_ops->vm_ops.close = coda_vm_close;
+		cvm_ops->coda_file = coda_file;
+		refcount_set(&cvm_ops->refcnt, 1);
+
+		vma->vm_ops = &cvm_ops->vm_ops;
+	}
+	return ret;
+}
+
+int coda_open(struct inode *coda_inode, struct file *coda_file)
+{
+	struct file *host_file = NULL;
+	int error;
+	unsigned short flags = coda_file->f_flags & (~O_EXCL);
+	unsigned short coda_flags = coda_flags_to_cflags(flags);
+	struct coda_file_info *cfi;
+
+	cfi = kmalloc_obj(struct coda_file_info);
+	if (!cfi)
+		return -ENOMEM;
+
+	error = venus_open(coda_inode->i_sb, coda_i2f(coda_inode), coda_flags,
+			   &host_file);
+	if (!host_file)
+		error = -EIO;
+
+	if (error) {
+		kfree(cfi);
+		return error;
+	}
+
+	host_file->f_flags |= coda_file->f_flags & (O_APPEND | O_SYNC);
+
+	cfi->cfi_magic = CODA_MAGIC;
+	cfi->cfi_mapcount = 0;
+	cfi->cfi_container = host_file;
+	/* assume access intents are supported unless we hear otherwise */
+	cfi->cfi_access_intent = true;
+
+	BUG_ON(coda_file->private_data != NULL);
+	coda_file->private_data = cfi;
+	return 0;
+}
+
+int coda_release(struct inode *coda_inode, struct file *coda_file)
+{
+	unsigned short flags = (coda_file->f_flags) & (~O_EXCL);
+	unsigned short coda_flags = coda_flags_to_cflags(flags);
+	struct coda_file_info *cfi;
+	struct coda_inode_info *cii;
+	struct inode *host_inode;
+
+	cfi = coda_ftoc(coda_file);
+
+	venus_close(coda_inode->i_sb, coda_i2f(coda_inode),
+			  coda_flags, coda_file->f_cred->fsuid);
+
+	host_inode = file_inode(cfi->cfi_container);
+	cii = ITOC(coda_inode);
+
+	/* did we mmap this file? */
+	spin_lock(&cii->c_lock);
+	if (coda_inode->i_mapping == &host_inode->i_data) {
+		cii->c_mapcount -= cfi->cfi_mapcount;
+		if (!cii->c_mapcount)
+			coda_inode->i_mapping = &coda_inode->i_data;
+	}
+	spin_unlock(&cii->c_lock);
+
+	fput(cfi->cfi_container);
+	kfree(coda_file->private_data);
+	coda_file->private_data = NULL;
+
+	/* VFS fput ignores the return value from file_operations->release, so
+	 * there is no use returning an error here */
+	return 0;
+}
+
+int coda_fsync(struct file *coda_file, loff_t start, loff_t end, int datasync)
+{
+	struct file *host_file;
+	struct inode *coda_inode = file_inode(coda_file);
+	struct coda_file_info *cfi;
+	int err;
+
+	if (!(S_ISREG(coda_inode->i_mode) || S_ISDIR(coda_inode->i_mode) ||
+	      S_ISLNK(coda_inode->i_mode)))
+		return -EINVAL;
+
+	err = filemap_write_and_wait_range(coda_inode->i_mapping, start, end);
+	if (err)
+		return err;
+	inode_lock(coda_inode);
+
+	cfi = coda_ftoc(coda_file);
+	host_file = cfi->cfi_container;
+
+	err = vfs_fsync(host_file, datasync);
+	if (!err && !datasync)
+		err = venus_fsync(coda_inode->i_sb, coda_i2f(coda_inode));
+	inode_unlock(coda_inode);
+
+	return err;
+}
+
+const struct file_operations coda_file_operations = {
+	.llseek		= generic_file_llseek,
+	.read_iter	= coda_file_read_iter,
+	.write_iter	= coda_file_write_iter,
+	.mmap		= coda_file_mmap,
+	.open		= coda_open,
+	.release	= coda_release,
+	.fsync		= coda_fsync,
+	.splice_read	= coda_file_splice_read,
+};