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, 208 insertions, 0 deletions

diff --git a/include/media/v4l2-event.h b/include/media/v4l2-event.h
new file mode 100644
index 000000000..3a0e25883
--- /dev/null
+++ b/include/media/v4l2-event.h
@@ -0,0 +1,208 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * v4l2-event.h
+ *
+ * V4L2 events.
+ *
+ * Copyright (C) 2009--2010 Nokia Corporation.
+ *
+ * Contact: Sakari Ailus <sakari.ailus@iki.fi>
+ */
+
+#ifndef V4L2_EVENT_H
+#define V4L2_EVENT_H
+
+#include <linux/types.h>
+#include <linux/videodev2.h>
+#include <linux/wait.h>
+
+struct v4l2_fh;
+struct v4l2_subdev;
+struct v4l2_subscribed_event;
+struct video_device;
+
+/**
+ * struct v4l2_kevent - Internal kernel event struct.
+ * @list:	List node for the v4l2_fh->available list.
+ * @sev:	Pointer to parent v4l2_subscribed_event.
+ * @event:	The event itself.
+ * @ts:		The timestamp of the event.
+ */
+struct v4l2_kevent {
+	struct list_head	list;
+	struct v4l2_subscribed_event *sev;
+	struct v4l2_event	event;
+	u64			ts;
+};
+
+/**
+ * struct v4l2_subscribed_event_ops - Subscribed event operations.
+ *
+ * @add:	Optional callback, called when a new listener is added
+ * @del:	Optional callback, called when a listener stops listening
+ * @replace:	Optional callback that can replace event 'old' with event 'new'.
+ * @merge:	Optional callback that can merge event 'old' into event 'new'.
+ */
+struct v4l2_subscribed_event_ops {
+	int  (*add)(struct v4l2_subscribed_event *sev, unsigned int elems);
+	void (*del)(struct v4l2_subscribed_event *sev);
+	void (*replace)(struct v4l2_event *old, const struct v4l2_event *new);
+	void (*merge)(const struct v4l2_event *old, struct v4l2_event *new);
+};
+
+/**
+ * struct v4l2_subscribed_event - Internal struct representing a subscribed
+ *		event.
+ *
+ * @list:	List node for the v4l2_fh->subscribed list.
+ * @type:	Event type.
+ * @id:	Associated object ID (e.g. control ID). 0 if there isn't any.
+ * @flags:	Copy of v4l2_event_subscription->flags.
+ * @fh:	Filehandle that subscribed to this event.
+ * @node:	List node that hooks into the object's event list
+ *		(if there is one).
+ * @ops:	v4l2_subscribed_event_ops
+ * @elems:	The number of elements in the events array.
+ * @first:	The index of the events containing the oldest available event.
+ * @in_use:	The number of queued events.
+ * @events:	An array of @elems events.
+ */
+struct v4l2_subscribed_event {
+	struct list_head	list;
+	u32			type;
+	u32			id;
+	u32			flags;
+	struct v4l2_fh		*fh;
+	struct list_head	node;
+	const struct v4l2_subscribed_event_ops *ops;
+	unsigned int		elems;
+	unsigned int		first;
+	unsigned int		in_use;
+	struct v4l2_kevent	events[] __counted_by(elems);
+};
+
+/**
+ * v4l2_event_dequeue - Dequeue events from video device.
+ *
+ * @fh: pointer to struct v4l2_fh
+ * @event: pointer to struct v4l2_event
+ * @nonblocking: if not zero, waits for an event to arrive
+ */
+int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
+		       int nonblocking);
+
+/**
+ * v4l2_event_queue - Queue events to video device.
+ *
+ * @vdev: pointer to &struct video_device
+ * @ev: pointer to &struct v4l2_event
+ *
+ * The event will be queued for all &struct v4l2_fh file handlers.
+ *
+ * .. note::
+ *    The driver's only responsibility is to fill in the type and the data
+ *    fields. The other fields will be filled in by V4L2.
+ */
+void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
+
+/**
+ * v4l2_event_queue_fh - Queue events to video device.
+ *
+ * @fh: pointer to &struct v4l2_fh
+ * @ev: pointer to &struct v4l2_event
+ *
+ *
+ * The event will be queued only for the specified &struct v4l2_fh file handler.
+ *
+ * .. note::
+ *    The driver's only responsibility is to fill in the type and the data
+ *    fields. The other fields will be filled in by V4L2.
+ */
+void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
+
+/**
+ * v4l2_event_wake_all - Wake all filehandles.
+ *
+ * Used when unregistering a video device.
+ *
+ * @vdev: pointer to &struct video_device
+ */
+void v4l2_event_wake_all(struct video_device *vdev);
+
+/**
+ * v4l2_event_pending - Check if an event is available
+ *
+ * @fh: pointer to &struct v4l2_fh
+ *
+ * Returns the number of pending events.
+ */
+int v4l2_event_pending(struct v4l2_fh *fh);
+
+/**
+ * v4l2_event_subscribe - Subscribes to an event
+ *
+ * @fh: pointer to &struct v4l2_fh
+ * @sub: pointer to &struct v4l2_event_subscription
+ * @elems: size of the events queue
+ * @ops: pointer to &v4l2_subscribed_event_ops
+ *
+ * .. note::
+ *
+ *    if @elems is zero, the framework will fill in a default value,
+ *    with is currently 1 element.
+ */
+int v4l2_event_subscribe(struct v4l2_fh *fh,
+			 const struct v4l2_event_subscription *sub,
+			 unsigned int elems,
+			 const struct v4l2_subscribed_event_ops *ops);
+/**
+ * v4l2_event_unsubscribe - Unsubscribes to an event
+ *
+ * @fh: pointer to &struct v4l2_fh
+ * @sub: pointer to &struct v4l2_event_subscription
+ */
+int v4l2_event_unsubscribe(struct v4l2_fh *fh,
+			   const struct v4l2_event_subscription *sub);
+/**
+ * v4l2_event_unsubscribe_all - Unsubscribes to all events
+ *
+ * @fh: pointer to &struct v4l2_fh
+ */
+void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);
+
+/**
+ * v4l2_event_subdev_unsubscribe - Subdev variant of v4l2_event_unsubscribe()
+ *
+ * @sd: pointer to &struct v4l2_subdev
+ * @fh: pointer to &struct v4l2_fh
+ * @sub: pointer to &struct v4l2_event_subscription
+ *
+ * .. note::
+ *
+ *	This function should be used for the &struct v4l2_subdev_core_ops
+ *	%unsubscribe_event field.
+ */
+int v4l2_event_subdev_unsubscribe(struct v4l2_subdev *sd,
+				  struct v4l2_fh *fh,
+				  struct v4l2_event_subscription *sub);
+/**
+ * v4l2_src_change_event_subscribe - helper function that calls
+ *	v4l2_event_subscribe() if the event is %V4L2_EVENT_SOURCE_CHANGE.
+ *
+ * @fh: pointer to struct v4l2_fh
+ * @sub: pointer to &struct v4l2_event_subscription
+ */
+int v4l2_src_change_event_subscribe(struct v4l2_fh *fh,
+				    const struct v4l2_event_subscription *sub);
+/**
+ * v4l2_src_change_event_subdev_subscribe - Variant of v4l2_event_subscribe(),
+ *	meant to subscribe only events of the type %V4L2_EVENT_SOURCE_CHANGE.
+ *
+ * @sd: pointer to &struct v4l2_subdev
+ * @fh: pointer to &struct v4l2_fh
+ * @sub: pointer to &struct v4l2_event_subscription
+ */
+int v4l2_src_change_event_subdev_subscribe(struct v4l2_subdev *sd,
+					   struct v4l2_fh *fh,
+					   struct v4l2_event_subscription *sub);
+#endif /* V4L2_EVENT_H */