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, 242 insertions, 0 deletions

diff --git a/include/sound/cs8403.h b/include/sound/cs8403.h
new file mode 100644
index 000000000..c27f77639
--- /dev/null
+++ b/include/sound/cs8403.h
@@ -0,0 +1,242 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef __SOUND_CS8403_H
+#define __SOUND_CS8403_H
+
+/*
+ *  Routines for Cirrus Logic CS8403/CS8404A IEC958 (S/PDIF) Transmitter
+ *  Copyright (c) by Jaroslav Kysela <perex@perex.cz>,
+ *		     Takashi Iwai <tiwai@suse.de>
+ */
+
+#ifdef SND_CS8403
+
+#ifndef SND_CS8403_DECL
+#define SND_CS8403_DECL static
+#endif
+#ifndef SND_CS8403_DECODE
+#define SND_CS8403_DECODE snd_cs8403_decode_spdif_bits
+#endif
+#ifndef SND_CS8403_ENCODE
+#define SND_CS8403_ENCODE snd_cs8403_encode_spdif_bits
+#endif
+
+
+SND_CS8403_DECL void SND_CS8403_DECODE(struct snd_aes_iec958 *diga, unsigned char bits)
+{
+	if (bits & 0x01) {	/* consumer */
+		if (!(bits & 0x02))
+			diga->status[0] |= IEC958_AES0_NONAUDIO;
+		if (!(bits & 0x08))
+			diga->status[0] |= IEC958_AES0_CON_NOT_COPYRIGHT;
+		switch (bits & 0x10) {
+		case 0x10: diga->status[0] |= IEC958_AES0_CON_EMPHASIS_NONE; break;
+		case 0x00: diga->status[0] |= IEC958_AES0_CON_EMPHASIS_5015; break;
+		}
+		if (!(bits & 0x80))
+			diga->status[1] |= IEC958_AES1_CON_ORIGINAL;
+		switch (bits & 0x60) {
+		case 0x00: diga->status[1] |= IEC958_AES1_CON_MAGNETIC_ID; break;
+		case 0x20: diga->status[1] |= IEC958_AES1_CON_DIGDIGCONV_ID; break;
+		case 0x40: diga->status[1] |= IEC958_AES1_CON_LASEROPT_ID; break;
+		case 0x60: diga->status[1] |= IEC958_AES1_CON_GENERAL; break;
+		}
+		switch (bits & 0x06) {
+		case 0x00: diga->status[3] |= IEC958_AES3_CON_FS_44100; break;
+		case 0x02: diga->status[3] |= IEC958_AES3_CON_FS_48000; break;
+		case 0x04: diga->status[3] |= IEC958_AES3_CON_FS_32000; break;
+		}
+	} else {
+		diga->status[0] = IEC958_AES0_PROFESSIONAL;
+		switch (bits & 0x18) {
+		case 0x00: diga->status[0] |= IEC958_AES0_PRO_FS_32000; break;
+		case 0x10: diga->status[0] |= IEC958_AES0_PRO_FS_44100; break;
+		case 0x08: diga->status[0] |= IEC958_AES0_PRO_FS_48000; break;
+		case 0x18: diga->status[0] |= IEC958_AES0_PRO_FS_NOTID; break;
+		}
+		switch (bits & 0x60) {
+		case 0x20: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_NONE; break;
+		case 0x40: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_5015; break;
+		case 0x00: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_CCITT; break;
+		case 0x60: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_NOTID; break;
+		}
+		if (bits & 0x80)
+			diga->status[1] |= IEC958_AES1_PRO_MODE_STEREOPHONIC;
+	}
+}
+
+SND_CS8403_DECL unsigned char SND_CS8403_ENCODE(struct snd_aes_iec958 *diga)
+{
+	unsigned char bits;
+
+	if (!(diga->status[0] & IEC958_AES0_PROFESSIONAL)) {
+		bits = 0x01;	/* consumer mode */
+		if (diga->status[0] & IEC958_AES0_NONAUDIO)
+			bits &= ~0x02;
+		else
+			bits |= 0x02;
+		if (diga->status[0] & IEC958_AES0_CON_NOT_COPYRIGHT)
+			bits &= ~0x08;
+		else
+			bits |= 0x08;
+		switch (diga->status[0] & IEC958_AES0_CON_EMPHASIS) {
+		default:
+		case IEC958_AES0_CON_EMPHASIS_NONE: bits |= 0x10; break;
+		case IEC958_AES0_CON_EMPHASIS_5015: bits |= 0x00; break;
+		}
+		if (diga->status[1] & IEC958_AES1_CON_ORIGINAL)
+			bits &= ~0x80;
+		else
+			bits |= 0x80;
+		if ((diga->status[1] & IEC958_AES1_CON_CATEGORY) == IEC958_AES1_CON_GENERAL)
+			bits |= 0x60;
+		else {
+			switch(diga->status[1] & IEC958_AES1_CON_MAGNETIC_MASK) {
+			case IEC958_AES1_CON_MAGNETIC_ID:
+				bits |= 0x00; break;
+			case IEC958_AES1_CON_DIGDIGCONV_ID:
+				bits |= 0x20; break;
+			default:
+			case IEC958_AES1_CON_LASEROPT_ID:
+				bits |= 0x40; break;
+			}
+		}
+		switch (diga->status[3] & IEC958_AES3_CON_FS) {
+		default:
+		case IEC958_AES3_CON_FS_44100: bits |= 0x00; break;
+		case IEC958_AES3_CON_FS_48000: bits |= 0x02; break;
+		case IEC958_AES3_CON_FS_32000: bits |= 0x04; break;
+		}
+	} else {
+		bits = 0x00;	/* professional mode */
+		if (diga->status[0] & IEC958_AES0_NONAUDIO)
+			bits &= ~0x02;
+		else
+			bits |= 0x02;
+		/* CHECKME: I'm not sure about the bit order in val here */
+		switch (diga->status[0] & IEC958_AES0_PRO_FS) {
+		case IEC958_AES0_PRO_FS_32000:	bits |= 0x00; break;
+		case IEC958_AES0_PRO_FS_44100:	bits |= 0x10; break;	/* 44.1kHz */
+		case IEC958_AES0_PRO_FS_48000:	bits |= 0x08; break;	/* 48kHz */
+		default:
+		case IEC958_AES0_PRO_FS_NOTID: bits |= 0x18; break;
+		}
+		switch (diga->status[0] & IEC958_AES0_PRO_EMPHASIS) {
+		case IEC958_AES0_PRO_EMPHASIS_NONE: bits |= 0x20; break;
+		case IEC958_AES0_PRO_EMPHASIS_5015: bits |= 0x40; break;
+		case IEC958_AES0_PRO_EMPHASIS_CCITT: bits |= 0x00; break;
+		default:
+		case IEC958_AES0_PRO_EMPHASIS_NOTID: bits |= 0x60; break;
+		}
+		switch (diga->status[1] & IEC958_AES1_PRO_MODE) {
+		case IEC958_AES1_PRO_MODE_TWO:
+		case IEC958_AES1_PRO_MODE_STEREOPHONIC: bits |= 0x00; break;
+		default: bits |= 0x80; break;
+		}
+	}
+	return bits;
+}
+
+#endif /* SND_CS8403 */
+
+#ifdef SND_CS8404
+
+#ifndef SND_CS8404_DECL
+#define SND_CS8404_DECL static
+#endif
+#ifndef SND_CS8404_DECODE
+#define SND_CS8404_DECODE snd_cs8404_decode_spdif_bits
+#endif
+#ifndef SND_CS8404_ENCODE
+#define SND_CS8404_ENCODE snd_cs8404_encode_spdif_bits
+#endif
+
+
+SND_CS8404_DECL void SND_CS8404_DECODE(struct snd_aes_iec958 *diga, unsigned char bits)
+{
+	if (bits & 0x10) {	/* consumer */
+		if (!(bits & 0x20))
+			diga->status[0] |= IEC958_AES0_CON_NOT_COPYRIGHT;
+		if (!(bits & 0x40))
+			diga->status[0] |= IEC958_AES0_CON_EMPHASIS_5015;
+		if (!(bits & 0x80))
+			diga->status[1] |= IEC958_AES1_CON_ORIGINAL;
+		switch (bits & 0x03) {
+		case 0x00: diga->status[1] |= IEC958_AES1_CON_DAT; break;
+		case 0x03: diga->status[1] |= IEC958_AES1_CON_GENERAL; break;
+		}
+		switch (bits & 0x06) {
+		case 0x02: diga->status[3] |= IEC958_AES3_CON_FS_32000; break;
+		case 0x04: diga->status[3] |= IEC958_AES3_CON_FS_48000; break;
+		case 0x06: diga->status[3] |= IEC958_AES3_CON_FS_44100; break;
+		}
+	} else {
+		diga->status[0] = IEC958_AES0_PROFESSIONAL;
+		if (!(bits & 0x04))
+			diga->status[0] |= IEC958_AES0_NONAUDIO;
+		switch (bits & 0x60) {
+		case 0x00: diga->status[0] |= IEC958_AES0_PRO_FS_32000; break;
+		case 0x40: diga->status[0] |= IEC958_AES0_PRO_FS_44100; break;
+		case 0x20: diga->status[0] |= IEC958_AES0_PRO_FS_48000; break;
+		case 0x60: diga->status[0] |= IEC958_AES0_PRO_FS_NOTID; break;
+		}
+		switch (bits & 0x03) {
+		case 0x02: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_NONE; break;
+		case 0x01: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_5015; break;
+		case 0x00: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_CCITT; break;
+		case 0x03: diga->status[0] |= IEC958_AES0_PRO_EMPHASIS_NOTID; break;
+		}
+		if (!(bits & 0x80))
+			diga->status[1] |= IEC958_AES1_PRO_MODE_STEREOPHONIC;
+	}
+}
+
+SND_CS8404_DECL unsigned char SND_CS8404_ENCODE(struct snd_aes_iec958 *diga)
+{
+	unsigned char bits;
+
+	if (!(diga->status[0] & IEC958_AES0_PROFESSIONAL)) {
+		bits = 0x10;	/* consumer mode */
+		if (!(diga->status[0] & IEC958_AES0_CON_NOT_COPYRIGHT))
+			bits |= 0x20;
+		if ((diga->status[0] & IEC958_AES0_CON_EMPHASIS) == IEC958_AES0_CON_EMPHASIS_NONE)
+			bits |= 0x40;
+		if (!(diga->status[1] & IEC958_AES1_CON_ORIGINAL))
+			bits |= 0x80;
+		if ((diga->status[1] & IEC958_AES1_CON_CATEGORY) == IEC958_AES1_CON_GENERAL)
+			bits |= 0x03;
+		switch (diga->status[3] & IEC958_AES3_CON_FS) {
+		default:
+		case IEC958_AES3_CON_FS_44100: bits |= 0x06; break;
+		case IEC958_AES3_CON_FS_48000: bits |= 0x04; break;
+		case IEC958_AES3_CON_FS_32000: bits |= 0x02; break;
+		}
+	} else {
+		bits = 0x00;	/* professional mode */
+		if (!(diga->status[0] & IEC958_AES0_NONAUDIO))
+			bits |= 0x04;
+		switch (diga->status[0] & IEC958_AES0_PRO_FS) {
+		case IEC958_AES0_PRO_FS_32000:	bits |= 0x00; break;
+		case IEC958_AES0_PRO_FS_44100:	bits |= 0x40; break;	/* 44.1kHz */
+		case IEC958_AES0_PRO_FS_48000:	bits |= 0x20; break;	/* 48kHz */
+		default:
+		case IEC958_AES0_PRO_FS_NOTID:	bits |= 0x00; break;
+		}
+		switch (diga->status[0] & IEC958_AES0_PRO_EMPHASIS) {
+		case IEC958_AES0_PRO_EMPHASIS_NONE: bits |= 0x02; break;
+		case IEC958_AES0_PRO_EMPHASIS_5015: bits |= 0x01; break;
+		case IEC958_AES0_PRO_EMPHASIS_CCITT: bits |= 0x00; break;
+		default:
+		case IEC958_AES0_PRO_EMPHASIS_NOTID: bits |= 0x03; break;
+		}
+		switch (diga->status[1] & IEC958_AES1_PRO_MODE) {
+		case IEC958_AES1_PRO_MODE_TWO:
+		case IEC958_AES1_PRO_MODE_STEREOPHONIC: bits |= 0x00; break;
+		default: bits |= 0x80; break;
+		}
+	}
+	return bits;
+}
+
+#endif /* SND_CS8404 */
+
+#endif /* __SOUND_CS8403_H */