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, 225 insertions, 0 deletions

diff --git a/include/trace/events/9p.h b/include/trace/events/9p.h
new file mode 100644
index 000000000..cd104a134
--- /dev/null
+++ b/include/trace/events/9p.h
@@ -0,0 +1,225 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM 9p
+
+#if !defined(_TRACE_9P_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_9P_H
+
+#include <linux/tracepoint.h>
+
+#define P9_MSG_T							\
+		EM( P9_TLERROR,		"P9_TLERROR" )			\
+		EM( P9_RLERROR,		"P9_RLERROR" )			\
+		EM( P9_TSTATFS,		"P9_TSTATFS" )			\
+		EM( P9_RSTATFS,		"P9_RSTATFS" )			\
+		EM( P9_TLOPEN,		"P9_TLOPEN" )			\
+		EM( P9_RLOPEN,		"P9_RLOPEN" )			\
+		EM( P9_TLCREATE,	"P9_TLCREATE" )			\
+		EM( P9_RLCREATE,	"P9_RLCREATE" )			\
+		EM( P9_TSYMLINK,	"P9_TSYMLINK" )			\
+		EM( P9_RSYMLINK,	"P9_RSYMLINK" )			\
+		EM( P9_TMKNOD,		"P9_TMKNOD" )			\
+		EM( P9_RMKNOD,		"P9_RMKNOD" )			\
+		EM( P9_TRENAME,		"P9_TRENAME" )			\
+		EM( P9_RRENAME,		"P9_RRENAME" )			\
+		EM( P9_TREADLINK,	"P9_TREADLINK" )		\
+		EM( P9_RREADLINK,	"P9_RREADLINK" )		\
+		EM( P9_TGETATTR,	"P9_TGETATTR" )			\
+		EM( P9_RGETATTR,	"P9_RGETATTR" )			\
+		EM( P9_TSETATTR,	"P9_TSETATTR" )			\
+		EM( P9_RSETATTR,	"P9_RSETATTR" )			\
+		EM( P9_TXATTRWALK,	"P9_TXATTRWALK" )		\
+		EM( P9_RXATTRWALK,	"P9_RXATTRWALK" )		\
+		EM( P9_TXATTRCREATE,	"P9_TXATTRCREATE" )		\
+		EM( P9_RXATTRCREATE,	"P9_RXATTRCREATE" )		\
+		EM( P9_TREADDIR,	"P9_TREADDIR" )			\
+		EM( P9_RREADDIR,	"P9_RREADDIR" )			\
+		EM( P9_TFSYNC,		"P9_TFSYNC" )			\
+		EM( P9_RFSYNC,		"P9_RFSYNC" )			\
+		EM( P9_TLOCK,		"P9_TLOCK" )			\
+		EM( P9_RLOCK,		"P9_RLOCK" )			\
+		EM( P9_TGETLOCK,	"P9_TGETLOCK" )			\
+		EM( P9_RGETLOCK,	"P9_RGETLOCK" )			\
+		EM( P9_TLINK,		"P9_TLINK" )			\
+		EM( P9_RLINK,		"P9_RLINK" )			\
+		EM( P9_TMKDIR,		"P9_TMKDIR" )			\
+		EM( P9_RMKDIR,		"P9_RMKDIR" )			\
+		EM( P9_TRENAMEAT,	"P9_TRENAMEAT" )		\
+		EM( P9_RRENAMEAT,	"P9_RRENAMEAT" )		\
+		EM( P9_TUNLINKAT,	"P9_TUNLINKAT" )		\
+		EM( P9_RUNLINKAT,	"P9_RUNLINKAT" )		\
+		EM( P9_TVERSION,	"P9_TVERSION" )			\
+		EM( P9_RVERSION,	"P9_RVERSION" )			\
+		EM( P9_TAUTH,		"P9_TAUTH" )			\
+		EM( P9_RAUTH,		"P9_RAUTH" )			\
+		EM( P9_TATTACH,		"P9_TATTACH" )			\
+		EM( P9_RATTACH,		"P9_RATTACH" )			\
+		EM( P9_TERROR,		"P9_TERROR" )			\
+		EM( P9_RERROR,		"P9_RERROR" )			\
+		EM( P9_TFLUSH,		"P9_TFLUSH" )			\
+		EM( P9_RFLUSH,		"P9_RFLUSH" )			\
+		EM( P9_TWALK,		"P9_TWALK" )			\
+		EM( P9_RWALK,		"P9_RWALK" )			\
+		EM( P9_TOPEN,		"P9_TOPEN" )			\
+		EM( P9_ROPEN,		"P9_ROPEN" )			\
+		EM( P9_TCREATE,		"P9_TCREATE" )			\
+		EM( P9_RCREATE,		"P9_RCREATE" )			\
+		EM( P9_TREAD,		"P9_TREAD" )			\
+		EM( P9_RREAD,		"P9_RREAD" )			\
+		EM( P9_TWRITE,		"P9_TWRITE" )			\
+		EM( P9_RWRITE,		"P9_RWRITE" )			\
+		EM( P9_TCLUNK,		"P9_TCLUNK" )			\
+		EM( P9_RCLUNK,		"P9_RCLUNK" )			\
+		EM( P9_TREMOVE,		"P9_TREMOVE" )			\
+		EM( P9_RREMOVE,		"P9_RREMOVE" )			\
+		EM( P9_TSTAT,		"P9_TSTAT" )			\
+		EM( P9_RSTAT,		"P9_RSTAT" )			\
+		EM( P9_TWSTAT,		"P9_TWSTAT" )			\
+		EMe(P9_RWSTAT,		"P9_RWSTAT" )
+
+
+#define P9_FID_REFTYPE							\
+		EM( P9_FID_REF_CREATE,	"create " )			\
+		EM( P9_FID_REF_GET,	"get    " )			\
+		EM( P9_FID_REF_PUT,	"put    " )			\
+		EMe(P9_FID_REF_DESTROY,	"destroy" )
+
+/* Define EM() to export the enums to userspace via TRACE_DEFINE_ENUM() */
+#undef EM
+#undef EMe
+#define EM(a, b)	TRACE_DEFINE_ENUM(a);
+#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
+
+P9_MSG_T
+P9_FID_REFTYPE
+
+/* And also use EM/EMe to define helper enums -- once */
+#ifndef __9P_DECLARE_TRACE_ENUMS_ONLY_ONCE
+#define __9P_DECLARE_TRACE_ENUMS_ONLY_ONCE
+#undef EM
+#undef EMe
+#define EM(a, b)	a,
+#define EMe(a, b)	a
+
+enum p9_fid_reftype {
+	P9_FID_REFTYPE
+} __mode(byte);
+
+#endif
+
+/*
+ * Now redefine the EM() and EMe() macros to map the enums to the strings
+ * that will be printed in the output.
+ */
+#undef EM
+#undef EMe
+#define EM(a, b)	{ a, b },
+#define EMe(a, b)	{ a, b }
+
+#define show_9p_op(type)						\
+	__print_symbolic(type, P9_MSG_T)
+#define show_9p_fid_reftype(type)					\
+	__print_symbolic(type, P9_FID_REFTYPE)
+
+TRACE_EVENT(9p_client_req,
+	    TP_PROTO(struct p9_client *clnt, int8_t type, int tag),
+
+	    TP_ARGS(clnt, type, tag),
+
+	    TP_STRUCT__entry(
+		    __field(    void *,		clnt			     )
+		    __field(	__u8,		type			     )
+		    __field(	__u32,		tag			     )
+		    ),
+
+	    TP_fast_assign(
+		    __entry->clnt    =  clnt;
+		    __entry->type    =  type;
+		    __entry->tag     =  tag;
+		    ),
+
+	    TP_printk("client %lu request %s tag  %d",
+		    (long)__entry->clnt, show_9p_op(__entry->type),
+		    __entry->tag)
+ );
+
+TRACE_EVENT(9p_client_res,
+	    TP_PROTO(struct p9_client *clnt, int8_t type, int tag, int err),
+
+	    TP_ARGS(clnt, type, tag, err),
+
+	    TP_STRUCT__entry(
+		    __field(    void *,		clnt			     )
+		    __field(	__u8,		type			     )
+		    __field(	__u32,		tag			     )
+		    __field(	__u32,		err			     )
+		    ),
+
+	    TP_fast_assign(
+		    __entry->clnt    =  clnt;
+		    __entry->type    =  type;
+		    __entry->tag     =  tag;
+		    __entry->err     =  err;
+		    ),
+
+	    TP_printk("client %lu response %s tag  %d err %d",
+		      (long)__entry->clnt, show_9p_op(__entry->type),
+		      __entry->tag, __entry->err)
+);
+
+/* dump 32 bytes of protocol data */
+#define P9_PROTO_DUMP_SZ 32
+TRACE_EVENT(9p_protocol_dump,
+	    TP_PROTO(struct p9_client *clnt, struct p9_fcall *pdu),
+
+	    TP_ARGS(clnt, pdu),
+
+	    TP_STRUCT__entry(
+		    __field(	void *,		clnt				)
+		    __field(	__u8,		type				)
+		    __field(	__u16,		tag				)
+		    __dynamic_array(unsigned char, line,
+				min_t(size_t, pdu->capacity, P9_PROTO_DUMP_SZ))
+		    ),
+
+	    TP_fast_assign(
+		    __entry->clnt   =  clnt;
+		    __entry->type   =  pdu->id;
+		    __entry->tag    =  pdu->tag;
+		    memcpy(__get_dynamic_array(line), pdu->sdata,
+				__get_dynamic_array_len(line));
+		    ),
+	    TP_printk("clnt %lu %s(tag = %d)\n%*ph\n",
+		      (unsigned long)__entry->clnt, show_9p_op(__entry->type),
+		      __entry->tag, __get_dynamic_array_len(line),
+		      __get_dynamic_array(line))
+ );
+
+
+TRACE_EVENT(9p_fid_ref,
+	    TP_PROTO(struct p9_fid *fid, __u8 type),
+
+	    TP_ARGS(fid, type),
+
+	    TP_STRUCT__entry(
+		    __field(	int,	fid		)
+		    __field(	int,	refcount	)
+		    __field(	__u8, type	)
+		    ),
+
+	    TP_fast_assign(
+		    __entry->fid = fid->fid;
+		    __entry->refcount = refcount_read(&fid->count);
+		    __entry->type = type;
+		    ),
+
+	    TP_printk("%s fid %d, refcount %d",
+		      show_9p_fid_reftype(__entry->type),
+		      __entry->fid, __entry->refcount)
+);
+
+
+#endif /* _TRACE_9P_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>