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, 34 insertions, 0 deletions

diff --git a/sound/firewire/fcp.h b/sound/firewire/fcp.h
new file mode 100644
index 000000000..512f7c409
--- /dev/null
+++ b/sound/firewire/fcp.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef SOUND_FIREWIRE_FCP_H_INCLUDED
+#define SOUND_FIREWIRE_FCP_H_INCLUDED
+
+#define	AVC_PLUG_INFO_BUF_BYTES	4
+
+struct fw_unit;
+
+/*
+ * AV/C Digital Interface Command Set General Specification 4.2
+ * (Sep 2004, 1394TA)
+ */
+enum avc_general_plug_dir {
+	AVC_GENERAL_PLUG_DIR_IN		= 0,
+	AVC_GENERAL_PLUG_DIR_OUT	= 1,
+	AVC_GENERAL_PLUG_DIR_COUNT
+};
+int avc_general_set_sig_fmt(struct fw_unit *unit, unsigned int rate,
+			    enum avc_general_plug_dir dir,
+			    unsigned short plug);
+int avc_general_get_sig_fmt(struct fw_unit *unit, unsigned int *rate,
+			    enum avc_general_plug_dir dir,
+			    unsigned short plug);
+int avc_general_get_plug_info(struct fw_unit *unit, unsigned int subunit_type,
+			      unsigned int subunit_id, unsigned int subfunction,
+			      u8 info[AVC_PLUG_INFO_BUF_BYTES]);
+
+int fcp_avc_transaction(struct fw_unit *unit,
+			const void *command, unsigned int command_size,
+			void *response, unsigned int response_size,
+			unsigned int response_match_bytes);
+void fcp_bus_reset(struct fw_unit *unit);
+
+#endif