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, 95 insertions, 0 deletions

diff --git a/fs/coda/coda_psdev.h b/fs/coda/coda_psdev.h
new file mode 100644
index 000000000..52da08c77
--- /dev/null
+++ b/fs/coda/coda_psdev.h
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __CODA_PSDEV_H
+#define __CODA_PSDEV_H
+
+#include <linux/backing-dev.h>
+#include <linux/magic.h>
+#include <linux/mutex.h>
+
+#define CODA_PSDEV_MAJOR 67
+#define MAX_CODADEVS  5	   /* how many do we allow */
+
+struct kstatfs;
+
+/* messages between coda filesystem in kernel and Venus */
+struct upc_req {
+	struct list_head	uc_chain;
+	caddr_t			uc_data;
+	u_short			uc_flags;
+	u_short			uc_inSize;  /* Size is at most 5000 bytes */
+	u_short			uc_outSize;
+	u_short			uc_opcode;  /* copied from data to save lookup */
+	int			uc_unique;
+	wait_queue_head_t	uc_sleep;   /* process' wait queue */
+};
+
+#define CODA_REQ_ASYNC  0x1
+#define CODA_REQ_READ   0x2
+#define CODA_REQ_WRITE  0x4
+#define CODA_REQ_ABORT  0x8
+
+/* communication pending/processing queues */
+struct venus_comm {
+	u_long		    vc_seq;
+	wait_queue_head_t   vc_waitq; /* Venus wait queue */
+	struct list_head    vc_pending;
+	struct list_head    vc_processing;
+	int                 vc_inuse;
+	struct super_block *vc_sb;
+	struct mutex	    vc_mutex;
+};
+
+static inline struct venus_comm *coda_vcp(struct super_block *sb)
+{
+	return (struct venus_comm *)((sb)->s_fs_info);
+}
+
+/* upcalls */
+int venus_rootfid(struct super_block *sb, struct CodaFid *fidp);
+int venus_getattr(struct super_block *sb, struct CodaFid *fid,
+		  struct coda_vattr *attr);
+int venus_setattr(struct super_block *, struct CodaFid *, struct coda_vattr *);
+int venus_lookup(struct super_block *sb, struct CodaFid *fid,
+		 const char *name, int length, int *type,
+		 struct CodaFid *resfid);
+int venus_close(struct super_block *sb, struct CodaFid *fid, int flags,
+		kuid_t uid);
+int venus_open(struct super_block *sb, struct CodaFid *fid, int flags,
+	       struct file **f);
+int venus_mkdir(struct super_block *sb, struct CodaFid *dirfid,
+		const char *name, int length,
+		struct CodaFid *newfid, struct coda_vattr *attrs);
+int venus_create(struct super_block *sb, struct CodaFid *dirfid,
+		 const char *name, int length, int excl, int mode,
+		 struct CodaFid *newfid, struct coda_vattr *attrs);
+int venus_rmdir(struct super_block *sb, struct CodaFid *dirfid,
+		const char *name, int length);
+int venus_remove(struct super_block *sb, struct CodaFid *dirfid,
+		 const char *name, int length);
+int venus_readlink(struct super_block *sb, struct CodaFid *fid,
+		   char *buffer, int *length);
+int venus_rename(struct super_block *sb, struct CodaFid *new_fid,
+		 struct CodaFid *old_fid, size_t old_length,
+		 size_t new_length, const char *old_name,
+		 const char *new_name);
+int venus_link(struct super_block *sb, struct CodaFid *fid,
+		  struct CodaFid *dirfid, const char *name, int len );
+int venus_symlink(struct super_block *sb, struct CodaFid *fid,
+		  const char *name, int len, const char *symname, int symlen);
+int venus_access(struct super_block *sb, struct CodaFid *fid, int mask);
+int venus_pioctl(struct super_block *sb, struct CodaFid *fid,
+		 unsigned int cmd, struct PioctlData *data);
+int coda_downcall(struct venus_comm *vcp, int opcode, union outputArgs *out,
+		  size_t nbytes);
+int venus_fsync(struct super_block *sb, struct CodaFid *fid);
+int venus_statfs(struct dentry *dentry, struct kstatfs *sfs);
+int venus_access_intent(struct super_block *sb, struct CodaFid *fid,
+			bool *access_intent_supported,
+			size_t count, loff_t ppos, int type);
+
+/*
+ * Statistics
+ */
+
+extern struct venus_comm coda_comms[];
+#endif