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, 268 insertions, 0 deletions

diff --git a/include/trace/events/v4l2.h b/include/trace/events/v4l2.h
new file mode 100644
index 000000000..248bc09bf
--- /dev/null
+++ b/include/trace/events/v4l2.h
@@ -0,0 +1,268 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM v4l2
+
+#if !defined(_TRACE_V4L2_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_V4L2_H
+
+#include <linux/tracepoint.h>
+#include <media/videobuf2-v4l2.h>
+
+/* Enums require being exported to userspace, for user tool parsing */
+#undef EM
+#undef EMe
+#define EM(a, b)	TRACE_DEFINE_ENUM(a);
+#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
+
+#define show_type(type)							\
+	__print_symbolic(type, SHOW_TYPE)
+
+#define SHOW_TYPE							\
+	EM( V4L2_BUF_TYPE_VIDEO_CAPTURE,	"VIDEO_CAPTURE" )	\
+	EM( V4L2_BUF_TYPE_VIDEO_OUTPUT,		"VIDEO_OUTPUT" )	\
+	EM( V4L2_BUF_TYPE_VIDEO_OVERLAY,	"VIDEO_OVERLAY" )	\
+	EM( V4L2_BUF_TYPE_VBI_CAPTURE,		"VBI_CAPTURE" )		\
+	EM( V4L2_BUF_TYPE_VBI_OUTPUT,		"VBI_OUTPUT" )		\
+	EM( V4L2_BUF_TYPE_SLICED_VBI_CAPTURE,   "SLICED_VBI_CAPTURE" )	\
+	EM( V4L2_BUF_TYPE_SLICED_VBI_OUTPUT,    "SLICED_VBI_OUTPUT" )	\
+	EM( V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY, "VIDEO_OUTPUT_OVERLAY" ) \
+	EM( V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE, "VIDEO_CAPTURE_MPLANE" ) \
+	EM( V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE,  "VIDEO_OUTPUT_MPLANE" )	\
+	EM( V4L2_BUF_TYPE_SDR_CAPTURE,          "SDR_CAPTURE" )		\
+	EM( V4L2_BUF_TYPE_SDR_OUTPUT,           "SDR_OUTPUT" )		\
+	EM( V4L2_BUF_TYPE_META_CAPTURE,		"META_CAPTURE" )	\
+	EMe(V4L2_BUF_TYPE_PRIVATE,		"PRIVATE" )
+
+SHOW_TYPE
+
+#define show_field(field)						\
+	__print_symbolic(field, SHOW_FIELD)
+
+#define SHOW_FIELD							\
+	EM( V4L2_FIELD_ANY,		"ANY" )				\
+	EM( V4L2_FIELD_NONE,		"NONE" )			\
+	EM( V4L2_FIELD_TOP,		"TOP" )				\
+	EM( V4L2_FIELD_BOTTOM,		"BOTTOM" )			\
+	EM( V4L2_FIELD_INTERLACED,	"INTERLACED" )			\
+	EM( V4L2_FIELD_SEQ_TB,		"SEQ_TB" )			\
+	EM( V4L2_FIELD_SEQ_BT,		"SEQ_BT" )			\
+	EM( V4L2_FIELD_ALTERNATE,	"ALTERNATE" )			\
+	EM( V4L2_FIELD_INTERLACED_TB,	"INTERLACED_TB" )		\
+	EMe( V4L2_FIELD_INTERLACED_BT,	"INTERLACED_BT" )
+
+SHOW_FIELD
+
+/*
+ * 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}
+
+/* V4L2_TC_TYPE_* are macros, not defines, they do not need processing */
+
+#define show_timecode_type(type)					\
+	__print_symbolic(type,						\
+		{ V4L2_TC_TYPE_24FPS,		"24FPS" },		\
+		{ V4L2_TC_TYPE_25FPS,		"25FPS" },		\
+		{ V4L2_TC_TYPE_30FPS,		"30FPS" },		\
+		{ V4L2_TC_TYPE_50FPS,		"50FPS" },		\
+		{ V4L2_TC_TYPE_60FPS,		"60FPS" })
+
+#define show_flags(flags)						      \
+	__print_flags(flags, "|",					      \
+		{ V4L2_BUF_FLAG_MAPPED,		     "MAPPED" },	      \
+		{ V4L2_BUF_FLAG_QUEUED,		     "QUEUED" },	      \
+		{ V4L2_BUF_FLAG_DONE,		     "DONE" },		      \
+		{ V4L2_BUF_FLAG_KEYFRAME,	     "KEYFRAME" },	      \
+		{ V4L2_BUF_FLAG_PFRAME,		     "PFRAME" },	      \
+		{ V4L2_BUF_FLAG_BFRAME,		     "BFRAME" },	      \
+		{ V4L2_BUF_FLAG_ERROR,		     "ERROR" },		      \
+		{ V4L2_BUF_FLAG_TIMECODE,	     "TIMECODE" },	      \
+		{ V4L2_BUF_FLAG_PREPARED,	     "PREPARED" },	      \
+		{ V4L2_BUF_FLAG_NO_CACHE_INVALIDATE, "NO_CACHE_INVALIDATE" }, \
+		{ V4L2_BUF_FLAG_NO_CACHE_CLEAN,	     "NO_CACHE_CLEAN" },      \
+		{ V4L2_BUF_FLAG_TIMESTAMP_MASK,	     "TIMESTAMP_MASK" },      \
+		{ V4L2_BUF_FLAG_TIMESTAMP_UNKNOWN,   "TIMESTAMP_UNKNOWN" },   \
+		{ V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC, "TIMESTAMP_MONOTONIC" }, \
+		{ V4L2_BUF_FLAG_TIMESTAMP_COPY,	     "TIMESTAMP_COPY" },      \
+		{ V4L2_BUF_FLAG_LAST,                "LAST" })
+
+#define show_timecode_flags(flags)					  \
+	__print_flags(flags, "|",					  \
+		{ V4L2_TC_FLAG_DROPFRAME,       "DROPFRAME" },		  \
+		{ V4L2_TC_FLAG_COLORFRAME,      "COLORFRAME" },		  \
+		{ V4L2_TC_USERBITS_USERDEFINED,	"USERBITS_USERDEFINED" }, \
+		{ V4L2_TC_USERBITS_8BITCHARS,	"USERBITS_8BITCHARS" })
+
+DECLARE_EVENT_CLASS(v4l2_event_class,
+	TP_PROTO(int minor, struct v4l2_buffer *buf),
+
+	TP_ARGS(minor, buf),
+
+	TP_STRUCT__entry(
+		__field(int, minor)
+		__field(u32, index)
+		__field(u32, type)
+		__field(u32, bytesused)
+		__field(u32, flags)
+		__field(u32, field)
+		__field(s64, timestamp)
+		__field(u32, timecode_type)
+		__field(u32, timecode_flags)
+		__field(u8, timecode_frames)
+		__field(u8, timecode_seconds)
+		__field(u8, timecode_minutes)
+		__field(u8, timecode_hours)
+		__field(u8, timecode_userbits0)
+		__field(u8, timecode_userbits1)
+		__field(u8, timecode_userbits2)
+		__field(u8, timecode_userbits3)
+		__field(u32, sequence)
+	),
+
+	TP_fast_assign(
+		__entry->minor = minor;
+		__entry->index = buf->index;
+		__entry->type = buf->type;
+		__entry->bytesused = buf->bytesused;
+		__entry->flags = buf->flags;
+		__entry->field = buf->field;
+		__entry->timestamp = v4l2_buffer_get_timestamp(buf);
+		__entry->timecode_type = buf->timecode.type;
+		__entry->timecode_flags = buf->timecode.flags;
+		__entry->timecode_frames = buf->timecode.frames;
+		__entry->timecode_seconds = buf->timecode.seconds;
+		__entry->timecode_minutes = buf->timecode.minutes;
+		__entry->timecode_hours = buf->timecode.hours;
+		__entry->timecode_userbits0 = buf->timecode.userbits[0];
+		__entry->timecode_userbits1 = buf->timecode.userbits[1];
+		__entry->timecode_userbits2 = buf->timecode.userbits[2];
+		__entry->timecode_userbits3 = buf->timecode.userbits[3];
+		__entry->sequence = buf->sequence;
+	),
+
+	TP_printk("minor = %d, index = %u, type = %s, bytesused = %u, "
+		  "flags = %s, field = %s, timestamp = %llu, "
+		  "timecode = { type = %s, flags = %s, frames = %u, "
+		  "seconds = %u, minutes = %u, hours = %u, "
+		  "userbits = { %u %u %u %u } }, sequence = %u", __entry->minor,
+		  __entry->index, show_type(__entry->type),
+		  __entry->bytesused,
+		  show_flags(__entry->flags),
+		  show_field(__entry->field),
+		  __entry->timestamp,
+		  show_timecode_type(__entry->timecode_type),
+		  show_timecode_flags(__entry->timecode_flags),
+		  __entry->timecode_frames,
+		  __entry->timecode_seconds,
+		  __entry->timecode_minutes,
+		  __entry->timecode_hours,
+		  __entry->timecode_userbits0,
+		  __entry->timecode_userbits1,
+		  __entry->timecode_userbits2,
+		  __entry->timecode_userbits3,
+		  __entry->sequence
+	)
+)
+
+DEFINE_EVENT(v4l2_event_class, v4l2_dqbuf,
+	TP_PROTO(int minor, struct v4l2_buffer *buf),
+	TP_ARGS(minor, buf)
+);
+
+DEFINE_EVENT(v4l2_event_class, v4l2_qbuf,
+	TP_PROTO(int minor, struct v4l2_buffer *buf),
+	TP_ARGS(minor, buf)
+);
+
+DECLARE_EVENT_CLASS(vb2_v4l2_event_class,
+	TP_PROTO(struct vb2_queue *q, struct vb2_buffer *vb),
+	TP_ARGS(q, vb),
+
+	TP_STRUCT__entry(
+		__field(int, minor)
+		__field(u32, flags)
+		__field(u32, field)
+		__field(u64, timestamp)
+		__field(u32, timecode_type)
+		__field(u32, timecode_flags)
+		__field(u8, timecode_frames)
+		__field(u8, timecode_seconds)
+		__field(u8, timecode_minutes)
+		__field(u8, timecode_hours)
+		__field(u8, timecode_userbits0)
+		__field(u8, timecode_userbits1)
+		__field(u8, timecode_userbits2)
+		__field(u8, timecode_userbits3)
+		__field(u32, sequence)
+	),
+
+	TP_fast_assign(
+		struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb);
+		struct v4l2_fh *owner = q->owner;
+
+		__entry->minor = owner ? owner->vdev->minor : -1;
+		__entry->flags = vbuf->flags;
+		__entry->field = vbuf->field;
+		__entry->timestamp = vb->timestamp;
+		__entry->timecode_type = vbuf->timecode.type;
+		__entry->timecode_flags = vbuf->timecode.flags;
+		__entry->timecode_frames = vbuf->timecode.frames;
+		__entry->timecode_seconds = vbuf->timecode.seconds;
+		__entry->timecode_minutes = vbuf->timecode.minutes;
+		__entry->timecode_hours = vbuf->timecode.hours;
+		__entry->timecode_userbits0 = vbuf->timecode.userbits[0];
+		__entry->timecode_userbits1 = vbuf->timecode.userbits[1];
+		__entry->timecode_userbits2 = vbuf->timecode.userbits[2];
+		__entry->timecode_userbits3 = vbuf->timecode.userbits[3];
+		__entry->sequence = vbuf->sequence;
+	),
+
+	TP_printk("minor=%d flags = %s, field = %s, "
+		  "timestamp = %llu, timecode = { type = %s, flags = %s, "
+		  "frames = %u, seconds = %u, minutes = %u, hours = %u, "
+		  "userbits = { %u %u %u %u } }, sequence = %u", __entry->minor,
+		  show_flags(__entry->flags),
+		  show_field(__entry->field),
+		  __entry->timestamp,
+		  show_timecode_type(__entry->timecode_type),
+		  show_timecode_flags(__entry->timecode_flags),
+		  __entry->timecode_frames,
+		  __entry->timecode_seconds,
+		  __entry->timecode_minutes,
+		  __entry->timecode_hours,
+		  __entry->timecode_userbits0,
+		  __entry->timecode_userbits1,
+		  __entry->timecode_userbits2,
+		  __entry->timecode_userbits3,
+		  __entry->sequence
+	)
+)
+
+DEFINE_EVENT(vb2_v4l2_event_class, vb2_v4l2_buf_done,
+	TP_PROTO(struct vb2_queue *q, struct vb2_buffer *vb),
+	TP_ARGS(q, vb)
+);
+
+DEFINE_EVENT(vb2_v4l2_event_class, vb2_v4l2_buf_queue,
+	TP_PROTO(struct vb2_queue *q, struct vb2_buffer *vb),
+	TP_ARGS(q, vb)
+);
+
+DEFINE_EVENT(vb2_v4l2_event_class, vb2_v4l2_dqbuf,
+	TP_PROTO(struct vb2_queue *q, struct vb2_buffer *vb),
+	TP_ARGS(q, vb)
+);
+
+DEFINE_EVENT(vb2_v4l2_event_class, vb2_v4l2_qbuf,
+	TP_PROTO(struct vb2_queue *q, struct vb2_buffer *vb),
+	TP_ARGS(q, vb)
+);
+
+#endif /* if !defined(_TRACE_V4L2_H) || defined(TRACE_HEADER_MULTI_READ) */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>