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, 179 insertions, 0 deletions

diff --git a/fs/coda/cnode.c b/fs/coda/cnode.c
new file mode 100644
index 000000000..70bb0579b
--- /dev/null
+++ b/fs/coda/cnode.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0
+/* cnode related routines for the coda kernel code
+   (C) 1996 Peter Braam
+   */
+
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/time.h>
+
+#include <linux/coda.h>
+#include <linux/pagemap.h>
+#include "coda_psdev.h"
+#include "coda_linux.h"
+
+static inline int coda_fideq(struct CodaFid *fid1, struct CodaFid *fid2)
+{
+	return memcmp(fid1, fid2, sizeof(*fid1)) == 0;
+}
+
+static const struct inode_operations coda_symlink_inode_operations = {
+	.get_link	= page_get_link,
+	.setattr	= coda_setattr,
+};
+
+/* cnode.c */
+static void coda_fill_inode(struct inode *inode, struct coda_vattr *attr)
+{
+        coda_vattr_to_iattr(inode, attr);
+
+        if (S_ISREG(inode->i_mode)) {
+                inode->i_op = &coda_file_inode_operations;
+                inode->i_fop = &coda_file_operations;
+        } else if (S_ISDIR(inode->i_mode)) {
+                inode->i_op = &coda_dir_inode_operations;
+                inode->i_fop = &coda_dir_operations;
+        } else if (S_ISLNK(inode->i_mode)) {
+		inode->i_op = &coda_symlink_inode_operations;
+		inode_nohighmem(inode);
+		inode->i_data.a_ops = &coda_symlink_aops;
+		inode->i_mapping = &inode->i_data;
+	} else
+                init_special_inode(inode, inode->i_mode, huge_decode_dev(attr->va_rdev));
+}
+
+static int coda_test_inode(struct inode *inode, void *data)
+{
+	struct CodaFid *fid = (struct CodaFid *)data;
+	struct coda_inode_info *cii = ITOC(inode);
+	return coda_fideq(&cii->c_fid, fid);
+}
+
+static int coda_set_inode(struct inode *inode, void *data)
+{
+	struct CodaFid *fid = (struct CodaFid *)data;
+	struct coda_inode_info *cii = ITOC(inode);
+	cii->c_fid = *fid;
+	return 0;
+}
+
+struct inode * coda_iget(struct super_block * sb, struct CodaFid * fid,
+			 struct coda_vattr * attr)
+{
+	struct inode *inode;
+	struct coda_inode_info *cii;
+	unsigned long hash = coda_f2i(fid);
+	umode_t inode_type = coda_inode_type(attr);
+
+retry:
+	inode = iget5_locked(sb, hash, coda_test_inode, coda_set_inode, fid);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	if (inode_state_read_once(inode) & I_NEW) {
+		cii = ITOC(inode);
+		/* we still need to set i_ino for things like stat(2) */
+		inode->i_ino = hash;
+		/* inode is locked and unique, no need to grab cii->c_lock */
+		cii->c_mapcount = 0;
+		coda_fill_inode(inode, attr);
+		unlock_new_inode(inode);
+	} else if ((inode->i_mode & S_IFMT) != inode_type) {
+		/* Inode has changed type, mark bad and grab a new one */
+		remove_inode_hash(inode);
+		coda_flag_inode(inode, C_PURGE);
+		iput(inode);
+		goto retry;
+	}
+	return inode;
+}
+
+/* this is effectively coda_iget:
+   - get attributes (might be cached)
+   - get the inode for the fid using vfs iget
+   - link the two up if this is needed
+   - fill in the attributes
+*/
+struct inode *coda_cnode_make(struct CodaFid *fid, struct super_block *sb)
+{
+        struct coda_vattr attr;
+	struct inode *inode;
+        int error;
+        
+	/* We get inode numbers from Venus -- see venus source */
+	error = venus_getattr(sb, fid, &attr);
+	if (error)
+		return ERR_PTR(error);
+
+	inode = coda_iget(sb, fid, &attr);
+	if (IS_ERR(inode))
+		pr_warn("%s: coda_iget failed\n", __func__);
+	return inode;
+}
+
+
+/* Although we treat Coda file identifiers as immutable, there is one
+ * special case for files created during a disconnection where they may
+ * not be globally unique. When an identifier collision is detected we
+ * first try to flush the cached inode from the kernel and finally
+ * resort to renaming/rehashing in-place. Userspace remembers both old
+ * and new values of the identifier to handle any in-flight upcalls.
+ * The real solution is to use globally unique UUIDs as identifiers, but
+ * retrofitting the existing userspace code for this is non-trivial. */
+void coda_replace_fid(struct inode *inode, struct CodaFid *oldfid, 
+		      struct CodaFid *newfid)
+{
+	struct coda_inode_info *cii = ITOC(inode);
+	unsigned long hash = coda_f2i(newfid);
+	
+	BUG_ON(!coda_fideq(&cii->c_fid, oldfid));
+
+	/* replace fid and rehash inode */
+	/* XXX we probably need to hold some lock here! */
+	remove_inode_hash(inode);
+	cii->c_fid = *newfid;
+	inode->i_ino = hash;
+	__insert_inode_hash(inode, hash);
+}
+
+/* convert a fid to an inode. */
+struct inode *coda_fid_to_inode(struct CodaFid *fid, struct super_block *sb) 
+{
+	struct inode *inode;
+	unsigned long hash = coda_f2i(fid);
+
+	inode = ilookup5(sb, hash, coda_test_inode, fid);
+	if ( !inode )
+		return NULL;
+
+	/* we should never see newly created inodes because we intentionally
+	 * fail in the initialization callback */
+	BUG_ON(inode_state_read_once(inode) & I_NEW);
+
+	return inode;
+}
+
+struct coda_file_info *coda_ftoc(struct file *file)
+{
+	struct coda_file_info *cfi = file->private_data;
+
+	BUG_ON(!cfi || cfi->cfi_magic != CODA_MAGIC);
+
+	return cfi;
+
+}
+
+/* the CONTROL inode is made without asking attributes from Venus */
+struct inode *coda_cnode_makectl(struct super_block *sb)
+{
+	struct inode *inode = new_inode(sb);
+	if (inode) {
+		inode->i_ino = CTL_INO;
+		inode->i_op = &coda_ioctl_inode_operations;
+		inode->i_fop = &coda_ioctl_operations;
+		inode->i_mode = 0444;
+		return inode;
+	}
+	return ERR_PTR(-ENOMEM);
+}
+