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, 45 insertions, 0 deletions

diff --git a/include/sound/tlv.h b/include/sound/tlv.h
new file mode 100644
index 000000000..5cff33a2d
--- /dev/null
+++ b/include/sound/tlv.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_TLV_H
+#define __SOUND_TLV_H
+
+/*
+ *  Advanced Linux Sound Architecture - ALSA - Driver
+ *  Copyright (c) 2006 by Jaroslav Kysela <perex@perex.cz>
+ */
+
+#include <uapi/sound/tlv.h>
+
+/* For historical reasons, these macros are aliases to the ones in UAPI. */
+#define TLV_ITEM			SNDRV_CTL_TLVD_ITEM
+#define TLV_LENGTH			SNDRV_CTL_TLVD_LENGTH
+
+#define TLV_CONTAINER_ITEM		SNDRV_CTL_TLVD_CONTAINER_ITEM
+#define DECLARE_TLV_CONTAINER		SNDRV_CTL_TLVD_DECLARE_CONTAINER
+
+#define TLV_DB_SCALE_MASK		SNDRV_CTL_TLVD_DB_SCALE_MASK
+#define TLV_DB_SCALE_MUTE		SNDRV_CTL_TLVD_DB_SCALE_MUTE
+#define TLV_DB_SCALE_ITEM		SNDRV_CTL_TLVD_DB_SCALE_ITEM
+#define DECLARE_TLV_DB_SCALE		SNDRV_CTL_TLVD_DECLARE_DB_SCALE
+
+#define TLV_DB_MINMAX_ITEM		SNDRV_CTL_TLVD_DB_MINMAX_ITEM
+#define TLV_DB_MINMAX_MUTE_ITEM		SNDRV_CTL_TLVD_DB_MINMAX_MUTE_ITEM
+#define DECLARE_TLV_DB_MINMAX		SNDRV_CTL_TLVD_DECLARE_DB_MINMAX
+#define DECLARE_TLV_DB_MINMAX_MUTE	SNDRV_CTL_TLVD_DECLARE_DB_MINMAX_MUTE
+
+#define TLV_DB_LINEAR_ITEM		SNDRV_CTL_TLVD_DB_LINEAR_ITEM
+#define DECLARE_TLV_DB_LINEAR		SNDRV_CTL_TLVD_DECLARE_DB_LINEAR
+
+#define TLV_DB_RANGE_ITEM		SNDRV_CTL_TLVD_DB_RANGE_ITEM
+#define DECLARE_TLV_DB_RANGE		SNDRV_CTL_TLVD_DECLARE_DB_RANGE
+
+#define TLV_DB_GAIN_MUTE		SNDRV_CTL_TLVD_DB_GAIN_MUTE
+
+/*
+ * The below assumes that each item TLV is 4 words like DB_SCALE or LINEAR.
+ * This is an old fasion and obsoleted by commit bf1d1c9b6179("ALSA: tlv: add
+ * DECLARE_TLV_DB_RANGE()").
+ */
+#define TLV_DB_RANGE_HEAD(num) \
+	SNDRV_CTL_TLVT_DB_RANGE, 6 * (num) * sizeof(unsigned int)
+
+#endif /* __SOUND_TLV_H */