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, 47 insertions, 0 deletions

diff --git a/include/sound/ump_convert.h b/include/sound/ump_convert.h
new file mode 100644
index 000000000..682499b87
--- /dev/null
+++ b/include/sound/ump_convert.h
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#ifndef __SOUND_UMP_CONVERT_H
+#define __SOUND_UMP_CONVERT_H
+
+#include <sound/ump_msg.h>
+
+/* context for converting from legacy control messages to UMP packet */
+struct ump_cvt_to_ump_bank {
+	bool rpn_set;
+	bool nrpn_set;
+	bool bank_set;
+	unsigned char cc_rpn_msb, cc_rpn_lsb;
+	unsigned char cc_nrpn_msb, cc_nrpn_lsb;
+	unsigned char cc_data_msb, cc_data_lsb;
+	unsigned char cc_bank_msb, cc_bank_lsb;
+	bool cc_data_msb_set, cc_data_lsb_set;
+};
+
+/* context for converting from MIDI1 byte stream to UMP packet */
+struct ump_cvt_to_ump {
+	/* MIDI1 intermediate buffer */
+	unsigned char buf[6]; /* up to 6 bytes for SysEx */
+	int len;
+	int cmd_bytes;
+
+	/* UMP output packet */
+	u32 ump[4];
+	int ump_bytes;
+
+	/* various status */
+	unsigned int in_sysex;
+	struct ump_cvt_to_ump_bank bank[16];	/* per channel */
+};
+
+int snd_ump_convert_from_ump(const u32 *data, unsigned char *dst,
+			     unsigned char *group_ret);
+void snd_ump_convert_to_ump(struct ump_cvt_to_ump *cvt, unsigned char group,
+			    unsigned int protocol, unsigned char c);
+
+/* reset the converter context, called at each open to ump */
+static inline void snd_ump_convert_reset(struct ump_cvt_to_ump *ctx)
+{
+	memset(ctx, 0, sizeof(*ctx));
+
+}
+
+#endif /* __SOUND_UMP_CONVERT_H */