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, 85 insertions, 0 deletions

diff --git a/fs/lockd/xdr.h b/fs/lockd/xdr.h
new file mode 100644
index 000000000..a1126cca9
--- /dev/null
+++ b/fs/lockd/xdr.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * XDR types for the NLM protocol
+ *
+ * Copyright (C) 1996 Olaf Kirch <okir@monad.swb.de>
+ */
+
+#ifndef _LOCKD_XDR_H
+#define _LOCKD_XDR_H
+
+#include <linux/fs.h>
+#include <linux/filelock.h>
+#include <linux/nfs.h>
+#include <linux/sunrpc/xdr.h>
+
+#define SM_MAXSTRLEN		1024
+#define SM_PRIV_SIZE		16
+
+struct nsm_private {
+	unsigned char		data[SM_PRIV_SIZE];
+};
+
+#define NLM_MAXCOOKIELEN    	32
+#define NLM_MAXSTRLEN		1024
+
+#define	nlm_granted		cpu_to_be32(NLM_LCK_GRANTED)
+#define	nlm_lck_denied		cpu_to_be32(NLM_LCK_DENIED)
+#define	nlm_lck_denied_nolocks	cpu_to_be32(NLM_LCK_DENIED_NOLOCKS)
+#define	nlm_lck_blocked		cpu_to_be32(NLM_LCK_BLOCKED)
+#define	nlm_lck_denied_grace_period	cpu_to_be32(NLM_LCK_DENIED_GRACE_PERIOD)
+
+/* Lock info passed via NLM */
+struct lockd_lock {
+	char *			caller;
+	unsigned int		len; 	/* length of "caller" */
+	struct nfs_fh		fh;
+	struct xdr_netobj	oh;
+	u32			svid;
+	u64			lock_start;
+	u64			lock_len;
+	struct file_lock	fl;
+};
+
+/*
+ *	NLM cookies. Technically they can be 1K, but Linux only uses 8 bytes.
+ *	FreeBSD uses 16, Apple Mac OS X 10.3 uses 20. Therefore we set it to
+ *	32 bytes.
+ */
+
+struct lockd_cookie {
+	unsigned char data[NLM_MAXCOOKIELEN];
+	unsigned int len;
+};
+
+/*
+ * Generic lockd arguments for all but sm_notify
+ */
+struct lockd_args {
+	struct lockd_cookie	cookie;
+	struct lockd_lock	lock;
+	u32			block;
+	u32			reclaim;
+	u32			state;
+};
+
+/*
+ * Generic lockd result
+ */
+struct lockd_res {
+	struct lockd_cookie	cookie;
+	__be32			status;
+	struct lockd_lock	lock;
+};
+
+/*
+ * statd callback when client has rebooted
+ */
+struct lockd_reboot {
+	char			*mon;
+	unsigned int		len;
+	u32			state;
+	struct nsm_private	priv;
+};
+
+#endif /* _LOCKD_XDR_H */