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, 38 insertions, 0 deletions

diff --git a/include/sound/sdca_hid.h b/include/sound/sdca_hid.h
new file mode 100644
index 000000000..18bebbe42
--- /dev/null
+++ b/include/sound/sdca_hid.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause) */
+/*
+ * The MIPI SDCA specification is available for public downloads at
+ * https://www.mipi.org/mipi-sdca-v1-0-download
+ *
+ */
+
+#ifndef __SDCA_HID_H__
+#define __SDCA_HID_H__
+
+struct device;
+struct sdw_slave;
+
+struct sdca_entity;
+struct sdca_interrupt;
+
+#if IS_ENABLED(CONFIG_SND_SOC_SDCA_HID)
+
+int sdca_add_hid_device(struct device *dev, struct sdw_slave *sdw,
+			struct sdca_entity *entity);
+int sdca_hid_process_report(struct sdca_interrupt *interrupt);
+
+#else
+
+static inline int sdca_add_hid_device(struct device *dev, struct sdw_slave *sdw,
+				      struct sdca_entity *entity)
+{
+	return 0;
+}
+
+static inline int sdca_hid_process_report(struct sdca_interrupt *interrupt)
+{
+	return 0;
+}
+
+#endif
+
+#endif /* __SDCA_HID_H__ */