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, 75 insertions, 0 deletions

diff --git a/include/sound/pcm_oss.h b/include/sound/pcm_oss.h
new file mode 100644
index 000000000..c96f23c77
--- /dev/null
+++ b/include/sound/pcm_oss.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_PCM_OSS_H
+#define __SOUND_PCM_OSS_H
+
+/*
+ *  Digital Audio (PCM) - OSS compatibility abstract layer
+ *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>
+ */
+
+struct snd_pcm_oss_setup {
+	char *task_name;
+	unsigned int disable:1,
+		     direct:1,
+		     block:1,
+		     nonblock:1,
+		     partialfrag:1,
+		     nosilence:1,
+		     buggyptr:1;
+	unsigned int periods;
+	unsigned int period_size;
+	struct snd_pcm_oss_setup *next;
+};
+
+struct snd_pcm_oss_runtime {
+	unsigned params: 1,			/* format/parameter change */
+		 prepare: 1,			/* need to prepare the operation */
+		 trigger: 1,			/* trigger flag */
+		 sync_trigger: 1;		/* sync trigger flag */
+	int rate;				/* requested rate */
+	int format;				/* requested OSS format */
+	unsigned int channels;			/* requested channels */
+	unsigned int fragshift;
+	unsigned int maxfrags;
+	unsigned int subdivision;		/* requested subdivision */
+	size_t period_bytes;			/* requested period size */
+	size_t period_frames;			/* period frames for poll */
+	size_t period_ptr;			/* actual write pointer to period */
+	unsigned int periods;
+	size_t buffer_bytes;			/* requested buffer size */
+	size_t bytes;				/* total # bytes processed */
+	size_t mmap_bytes;
+	char *buffer;				/* vmallocated period */
+	size_t buffer_used;			/* used length from period buffer */
+	struct mutex params_lock;
+	atomic_t rw_ref;		/* concurrent read/write accesses */
+#ifdef CONFIG_SND_PCM_OSS_PLUGINS
+	struct snd_pcm_plugin *plugin_first;
+	struct snd_pcm_plugin *plugin_last;
+#endif
+	unsigned int prev_hw_ptr_period;
+};
+
+struct snd_pcm_oss_file {
+	struct snd_pcm_substream *streams[2];
+};
+
+struct snd_pcm_oss_substream {
+	unsigned oss: 1;			/* oss mode */
+	struct snd_pcm_oss_setup setup;		/* active setup */
+};
+
+struct snd_pcm_oss_stream {
+	struct snd_pcm_oss_setup *setup_list;	/* setup list */
+	struct mutex setup_mutex;
+#ifdef CONFIG_SND_VERBOSE_PROCFS
+	struct snd_info_entry *proc_entry;
+#endif
+};
+
+struct snd_pcm_oss {
+	int reg;
+	unsigned int reg_mask;
+};
+
+#endif /* __SOUND_PCM_OSS_H */