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, 35 insertions, 0 deletions

diff --git a/include/sound/graph_card.h b/include/sound/graph_card.h
new file mode 100644
index 000000000..8e2e15dfc
--- /dev/null
+++ b/include/sound/graph_card.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * ASoC audio graph card support
+ *
+ */
+
+#ifndef __GRAPH_CARD_H
+#define __GRAPH_CARD_H
+
+#include <sound/simple_card_utils.h>
+
+typedef int (*GRAPH2_CUSTOM)(struct simple_util_priv *priv,
+			     struct device_node *lnk,
+			     struct link_info *li);
+
+struct graph2_custom_hooks {
+	int (*hook_pre)(struct simple_util_priv *priv);
+	int (*hook_post)(struct simple_util_priv *priv);
+	GRAPH2_CUSTOM custom_normal;
+	GRAPH2_CUSTOM custom_dpcm;
+	GRAPH2_CUSTOM custom_c2c;
+};
+
+int audio_graph_parse_of(struct simple_util_priv *priv, struct device *dev);
+int audio_graph2_parse_of(struct simple_util_priv *priv, struct device *dev,
+			  struct graph2_custom_hooks *hooks);
+
+int audio_graph2_link_normal(struct simple_util_priv *priv,
+			     struct device_node *lnk, struct link_info *li);
+int audio_graph2_link_dpcm(struct simple_util_priv *priv,
+			   struct device_node *lnk, struct link_info *li);
+int audio_graph2_link_c2c(struct simple_util_priv *priv,
+			  struct device_node *lnk, struct link_info *li);
+
+#endif /* __GRAPH_CARD_H */