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, 83 insertions, 0 deletions

diff --git a/include/sound/seq_oss.h b/include/sound/seq_oss.h
new file mode 100644
index 000000000..7bf10a0fa
--- /dev/null
+++ b/include/sound/seq_oss.h
@@ -0,0 +1,83 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_SEQ_OSS_H
+#define __SOUND_SEQ_OSS_H
+
+/*
+ * OSS compatible sequencer driver
+ *
+ * Copyright (C) 1998,99 Takashi Iwai
+ */
+
+#include <sound/asequencer.h>
+#include <sound/seq_kernel.h>
+
+/*
+ * argument structure for synthesizer operations
+ */
+struct snd_seq_oss_arg {
+	/* given by OSS sequencer */
+	int app_index;	/* application unique index */
+	int file_mode;	/* file mode - see below */
+	int seq_mode;	/* sequencer mode - see below */
+
+	/* following must be initialized in open callback */
+	struct snd_seq_addr addr;	/* opened port address */
+	void *private_data;	/* private data for lowlevel drivers */
+
+	/* note-on event passing mode: initially given by OSS seq,
+	 * but configurable by drivers - see below
+	 */
+	int event_passing;
+};
+
+
+/*
+ * synthesizer operation callbacks
+ */
+struct snd_seq_oss_callback {
+	struct module *owner;
+	int (*open)(struct snd_seq_oss_arg *p, void *closure);
+	int (*close)(struct snd_seq_oss_arg *p);
+	int (*ioctl)(struct snd_seq_oss_arg *p, unsigned int cmd, unsigned long arg);
+	int (*load_patch)(struct snd_seq_oss_arg *p, int format, const char __user *buf, int offs, int count);
+	int (*reset)(struct snd_seq_oss_arg *p);
+	int (*raw_event)(struct snd_seq_oss_arg *p, unsigned char *data);
+};
+
+/* flag: file_mode */
+#define SNDRV_SEQ_OSS_FILE_ACMODE		3
+#define SNDRV_SEQ_OSS_FILE_READ		1
+#define SNDRV_SEQ_OSS_FILE_WRITE		2
+#define SNDRV_SEQ_OSS_FILE_NONBLOCK	4
+
+/* flag: seq_mode */
+#define SNDRV_SEQ_OSS_MODE_SYNTH		0
+#define SNDRV_SEQ_OSS_MODE_MUSIC		1
+
+/* flag: event_passing */
+#define SNDRV_SEQ_OSS_PROCESS_EVENTS	0	/* key == 255 is processed as velocity change */
+#define SNDRV_SEQ_OSS_PASS_EVENTS		1	/* pass all events to callback */
+#define SNDRV_SEQ_OSS_PROCESS_KEYPRESS	2	/* key >= 128 will be processed as key-pressure */
+
+/* default control rate: fixed */
+#define SNDRV_SEQ_OSS_CTRLRATE		100
+
+/* default max queue length: configurable by module option */
+#define SNDRV_SEQ_OSS_MAX_QLEN		1024
+
+
+/*
+ * data pointer to snd_seq_register_device
+ */
+struct snd_seq_oss_reg {
+	int type;
+	int subtype;
+	int nvoices;
+	struct snd_seq_oss_callback oper;
+	void *private_data;
+};
+
+/* device id */
+#define SNDRV_SEQ_DEV_ID_OSS		"seq-oss"
+
+#endif /* __SOUND_SEQ_OSS_H */