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, 107 insertions, 0 deletions

diff --git a/fs/lockd/trace.h b/fs/lockd/trace.h
new file mode 100644
index 000000000..a11d04e8c
--- /dev/null
+++ b/fs/lockd/trace.h
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM lockd
+
+#if !defined(_TRACE_LOCKD_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_LOCKD_H
+
+#include <linux/tracepoint.h>
+#include <linux/crc32.h>
+#include <linux/nfs.h>
+
+#include "lockd.h"
+
+#ifdef CONFIG_LOCKD_V4
+#define NLM_STATUS_LIST					\
+	nlm_status_code(LCK_GRANTED)			\
+	nlm_status_code(LCK_DENIED)			\
+	nlm_status_code(LCK_DENIED_NOLOCKS)		\
+	nlm_status_code(LCK_BLOCKED)			\
+	nlm_status_code(LCK_DENIED_GRACE_PERIOD)	\
+	nlm_status_code(DEADLCK)			\
+	nlm_status_code(ROFS)				\
+	nlm_status_code(STALE_FH)			\
+	nlm_status_code(FBIG)				\
+	nlm_status_code_end(FAILED)
+#else
+#define NLM_STATUS_LIST					\
+	nlm_status_code(LCK_GRANTED)			\
+	nlm_status_code(LCK_DENIED)			\
+	nlm_status_code(LCK_DENIED_NOLOCKS)		\
+	nlm_status_code(LCK_BLOCKED)			\
+	nlm_status_code_end(LCK_DENIED_GRACE_PERIOD)
+#endif
+
+#undef nlm_status_code
+#undef nlm_status_code_end
+#define nlm_status_code(x)	TRACE_DEFINE_ENUM(NLM_##x);
+#define nlm_status_code_end(x)	TRACE_DEFINE_ENUM(NLM_##x);
+
+NLM_STATUS_LIST
+
+#undef nlm_status_code
+#undef nlm_status_code_end
+#define nlm_status_code(x)	{ NLM_##x, #x },
+#define nlm_status_code_end(x)	{ NLM_##x, #x }
+
+#define show_nlm_status(x)	__print_symbolic(x, NLM_STATUS_LIST)
+
+DECLARE_EVENT_CLASS(nlmclnt_lock_event,
+		TP_PROTO(
+			const struct lockd_lock *lock,
+			const struct sockaddr *addr,
+			unsigned int addrlen,
+			__be32 status
+		),
+
+		TP_ARGS(lock, addr, addrlen, status),
+
+		TP_STRUCT__entry(
+			__field(u32, oh)
+			__field(u32, svid)
+			__field(u32, fh)
+			__field(unsigned long, status)
+			__field(loff_t, start)
+			__field(loff_t, end)
+			__sockaddr(addr, addrlen)
+		),
+
+		TP_fast_assign(
+			__entry->oh = ~crc32_le(0xffffffff, lock->oh.data, lock->oh.len);
+			__entry->svid = lock->svid;
+			__entry->fh = nfs_fhandle_hash(&lock->fh);
+			__entry->start = lock->fl.fl_start;
+			__entry->end = lock->fl.fl_end;
+			__entry->status = be32_to_cpu(status);
+			__assign_sockaddr(addr, addr, addrlen);
+		),
+
+		TP_printk(
+			"addr=%pISpc oh=0x%08x svid=0x%08x fh=0x%08x start=%lld end=%lld status=%s",
+			__get_sockaddr(addr), __entry->oh, __entry->svid,
+			__entry->fh, __entry->start, __entry->end,
+			show_nlm_status(__entry->status)
+		)
+);
+
+#define DEFINE_NLMCLNT_EVENT(name)				\
+	DEFINE_EVENT(nlmclnt_lock_event, name,			\
+			TP_PROTO(				\
+				const struct lockd_lock *lock,	\
+				const struct sockaddr *addr,	\
+				unsigned int addrlen,		\
+				__be32	status			\
+			),					\
+			TP_ARGS(lock, addr, addrlen, status))
+
+DEFINE_NLMCLNT_EVENT(nlmclnt_test);
+DEFINE_NLMCLNT_EVENT(nlmclnt_lock);
+DEFINE_NLMCLNT_EVENT(nlmclnt_unlock);
+DEFINE_NLMCLNT_EVENT(nlmclnt_grant);
+
+#endif /* _TRACE_LOCKD_H */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE trace
+#include <trace/define_trace.h>