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, 32 insertions, 0 deletions

diff --git a/include/sound/soc-link.h b/include/sound/soc-link.h
new file mode 100644
index 000000000..9314cde17
--- /dev/null
+++ b/include/sound/soc-link.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * soc-link.h
+ *
+ * Copyright (C) 2019 Renesas Electronics Corp.
+ * Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
+ */
+#ifndef __SOC_LINK_H
+#define __SOC_LINK_H
+
+int snd_soc_link_init(struct snd_soc_pcm_runtime *rtd);
+void snd_soc_link_exit(struct snd_soc_pcm_runtime *rtd);
+int snd_soc_link_be_hw_params_fixup(struct snd_soc_pcm_runtime *rtd,
+				    struct snd_pcm_hw_params *params);
+
+int snd_soc_link_startup(struct snd_pcm_substream *substream);
+void snd_soc_link_shutdown(struct snd_pcm_substream *substream,
+			   int rollback);
+int snd_soc_link_prepare(struct snd_pcm_substream *substream);
+int snd_soc_link_hw_params(struct snd_pcm_substream *substream,
+			   struct snd_pcm_hw_params *params);
+void snd_soc_link_hw_free(struct snd_pcm_substream *substream,
+			  int rollback);
+
+int snd_soc_link_trigger(struct snd_pcm_substream *substream, int cmd,
+			 int rollback);
+int snd_soc_link_compr_startup(struct snd_compr_stream *cstream);
+void snd_soc_link_compr_shutdown(struct snd_compr_stream *cstream,
+				 int rollback);
+int snd_soc_link_compr_set_params(struct snd_compr_stream *cstream);
+
+#endif /* __SOC_LINK_H */