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, 69 insertions, 0 deletions

diff --git a/include/sound/seq_virmidi.h b/include/sound/seq_virmidi.h
new file mode 100644
index 000000000..56a3f38df
--- /dev/null
+++ b/include/sound/seq_virmidi.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_SEQ_VIRMIDI_H
+#define __SOUND_SEQ_VIRMIDI_H
+
+/*
+ *  Virtual Raw MIDI client on Sequencer
+ *  Copyright (c) 2000 by Takashi Iwai <tiwai@suse.de>,
+ *                        Jaroslav Kysela <perex@perex.cz>
+ */
+
+#include <sound/rawmidi.h>
+#include <sound/seq_midi_event.h>
+
+/*
+ * device file instance:
+ * This instance is created at each time the midi device file is
+ * opened.  Each instance has its own input buffer and MIDI parser
+ * (buffer), and is associated with the device instance.
+ */
+struct snd_virmidi {
+	struct list_head list;
+	int seq_mode;
+	int client;
+	int port;
+	bool trigger;
+	struct snd_midi_event *parser;
+	struct snd_seq_event event;
+	struct snd_virmidi_dev *rdev;
+	struct snd_rawmidi_substream *substream;
+	struct work_struct output_work;
+};
+
+#define SNDRV_VIRMIDI_SUBSCRIBE		(1<<0)
+#define SNDRV_VIRMIDI_USE		(1<<1)
+
+/*
+ * device record:
+ * Each virtual midi device has one device instance.  It contains
+ * common information and the linked-list of opened files, 
+ */
+struct snd_virmidi_dev {
+	struct snd_card *card;		/* associated card */
+	struct snd_rawmidi *rmidi;		/* rawmidi device */
+	int seq_mode;			/* SNDRV_VIRMIDI_XXX */
+	int device;			/* sequencer device */
+	int client;			/* created/attached client */
+	int port;			/* created/attached port */
+	unsigned int flags;		/* SNDRV_VIRMIDI_* */
+	rwlock_t filelist_lock;
+	struct rw_semaphore filelist_sem;
+	struct list_head filelist;
+};
+
+/* sequencer mode:
+ * ATTACH = input/output events from midi device are routed to the
+ *          attached sequencer port.  sequencer port is not created
+ *          by virmidi itself.
+ *          the input to rawmidi must be processed by passing the
+ *          incoming events via snd_virmidi_receive()
+ * DISPATCH = input/output events are routed to subscribers.
+ *            sequencer port is created in virmidi.
+ */
+#define SNDRV_VIRMIDI_SEQ_NONE		0
+#define SNDRV_VIRMIDI_SEQ_ATTACH	1
+#define SNDRV_VIRMIDI_SEQ_DISPATCH	2
+
+int snd_virmidi_new(struct snd_card *card, int device, struct snd_rawmidi **rrmidi);
+
+#endif /* __SOUND_SEQ_VIRMIDI */