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, 286 insertions, 0 deletions

diff --git a/lib/decompress_unlzo.c b/lib/decompress_unlzo.c
new file mode 100644
index 000000000..57a9e9374
--- /dev/null
+++ b/lib/decompress_unlzo.c
@@ -0,0 +1,286 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * LZO decompressor for the Linux kernel. Code borrowed from the lzo
+ * implementation by Markus Franz Xaver Johannes Oberhumer.
+ *
+ * Linux kernel adaptation:
+ * Copyright (C) 2009
+ * Albin Tonnerre, Free Electrons <albin.tonnerre@free-electrons.com>
+ *
+ * Original code:
+ * Copyright (C) 1996-2005 Markus Franz Xaver Johannes Oberhumer
+ * All Rights Reserved.
+ *
+ * Markus F.X.J. Oberhumer
+ * <markus@oberhumer.com>
+ * http://www.oberhumer.com/opensource/lzop/
+ */
+
+#ifdef STATIC
+#define PREBOOT
+#include "lzo/lzo1x_decompress_safe.c"
+#else
+#include <linux/decompress/unlzo.h>
+#endif
+
+#include <linux/types.h>
+#include <linux/lzo.h>
+#include <linux/decompress/mm.h>
+
+#include <linux/compiler.h>
+#include <linux/unaligned.h>
+
+static const unsigned char lzop_magic[] = {
+	0x89, 0x4c, 0x5a, 0x4f, 0x00, 0x0d, 0x0a, 0x1a, 0x0a };
+
+#define LZO_BLOCK_SIZE        (256*1024l)
+#define HEADER_HAS_FILTER      0x00000800L
+#define HEADER_SIZE_MIN       (9 + 7     + 4 + 8     + 1       + 4)
+#define HEADER_SIZE_MAX       (9 + 7 + 1 + 8 + 8 + 4 + 1 + 255 + 4)
+
+STATIC inline long INIT parse_header(u8 *input, long *skip, long in_len)
+{
+	int l;
+	u8 *parse = input;
+	u8 *end = input + in_len;
+	u16 version;
+
+	/*
+	 * Check that there's enough input to possibly have a valid header.
+	 * Then it is possible to parse several fields until the minimum
+	 * size may have been used.
+	 */
+	if (in_len < HEADER_SIZE_MIN)
+		return 0;
+
+	/* read magic: 9 first bits */
+	for (l = 0; l < 9; l++) {
+		if (*parse++ != lzop_magic[l])
+			return 0;
+	}
+	/* get version (2bytes), skip library version (2),
+	 * 'need to be extracted' version (2) and
+	 * method (1) */
+	version = get_unaligned_be16(parse);
+	parse += 7;
+	if (version >= 0x0940)
+		parse++;
+	if (get_unaligned_be32(parse) & HEADER_HAS_FILTER)
+		parse += 8; /* flags + filter info */
+	else
+		parse += 4; /* flags */
+
+	/*
+	 * At least mode, mtime_low, filename length, and checksum must
+	 * be left to be parsed. If also mtime_high is present, it's OK
+	 * because the next input buffer check is after reading the
+	 * filename length.
+	 */
+	if (end - parse < 8 + 1 + 4)
+		return 0;
+
+	/* skip mode and mtime_low */
+	parse += 8;
+	if (version >= 0x0940)
+		parse += 4;	/* skip mtime_high */
+
+	l = *parse++;
+	/* don't care about the file name, and skip checksum */
+	if (end - parse < l + 4)
+		return 0;
+	parse += l + 4;
+
+	*skip = parse - input;
+	return 1;
+}
+
+STATIC int INIT unlzo(u8 *input, long in_len,
+				long (*fill)(void *, unsigned long),
+				long (*flush)(void *, unsigned long),
+				u8 *output, long *posp,
+				void (*error) (char *x))
+{
+	u8 r = 0;
+	long skip = 0;
+	u32 src_len, dst_len;
+	size_t tmp;
+	u8 *in_buf, *in_buf_save, *out_buf;
+	int ret = -1;
+
+	if (output) {
+		out_buf = output;
+	} else if (!flush) {
+		error("NULL output pointer and no flush function provided");
+		goto exit;
+	} else {
+		out_buf = malloc(LZO_BLOCK_SIZE);
+		if (!out_buf) {
+			error("Could not allocate output buffer");
+			goto exit;
+		}
+	}
+
+	if (input && fill) {
+		error("Both input pointer and fill function provided, don't know what to do");
+		goto exit_1;
+	} else if (input) {
+		in_buf = input;
+	} else if (!fill) {
+		error("NULL input pointer and missing fill function");
+		goto exit_1;
+	} else {
+		in_buf = malloc(lzo1x_worst_compress(LZO_BLOCK_SIZE));
+		if (!in_buf) {
+			error("Could not allocate input buffer");
+			goto exit_1;
+		}
+	}
+	in_buf_save = in_buf;
+
+	if (posp)
+		*posp = 0;
+
+	if (fill) {
+		/*
+		 * Start from in_buf + HEADER_SIZE_MAX to make it possible
+		 * to use memcpy() to copy the unused data to the beginning
+		 * of the buffer. This way memmove() isn't needed which
+		 * is missing from pre-boot environments of most archs.
+		 */
+		in_buf += HEADER_SIZE_MAX;
+		in_len = fill(in_buf, HEADER_SIZE_MAX);
+	}
+
+	if (!parse_header(in_buf, &skip, in_len)) {
+		error("invalid header");
+		goto exit_2;
+	}
+	in_buf += skip;
+	in_len -= skip;
+
+	if (fill) {
+		/* Move the unused data to the beginning of the buffer. */
+		memcpy(in_buf_save, in_buf, in_len);
+		in_buf = in_buf_save;
+	}
+
+	if (posp)
+		*posp = skip;
+
+	for (;;) {
+		/* read uncompressed block size */
+		if (fill && in_len < 4) {
+			skip = fill(in_buf + in_len, 4 - in_len);
+			if (skip > 0)
+				in_len += skip;
+		}
+		if (in_len < 4) {
+			error("file corrupted");
+			goto exit_2;
+		}
+		dst_len = get_unaligned_be32(in_buf);
+		in_buf += 4;
+		in_len -= 4;
+
+		/* exit if last block */
+		if (dst_len == 0) {
+			if (posp)
+				*posp += 4;
+			break;
+		}
+
+		if (dst_len > LZO_BLOCK_SIZE) {
+			error("dest len longer than block size");
+			goto exit_2;
+		}
+
+		/* read compressed block size, and skip block checksum info */
+		if (fill && in_len < 8) {
+			skip = fill(in_buf + in_len, 8 - in_len);
+			if (skip > 0)
+				in_len += skip;
+		}
+		if (in_len < 8) {
+			error("file corrupted");
+			goto exit_2;
+		}
+		src_len = get_unaligned_be32(in_buf);
+		in_buf += 8;
+		in_len -= 8;
+
+		if (src_len <= 0 || src_len > dst_len) {
+			error("file corrupted");
+			goto exit_2;
+		}
+
+		/* decompress */
+		if (fill && in_len < src_len) {
+			skip = fill(in_buf + in_len, src_len - in_len);
+			if (skip > 0)
+				in_len += skip;
+		}
+		if (in_len < src_len) {
+			error("file corrupted");
+			goto exit_2;
+		}
+		tmp = dst_len;
+
+		/* When the input data is not compressed at all,
+		 * lzo1x_decompress_safe will fail, so call memcpy()
+		 * instead */
+		if (unlikely(dst_len == src_len))
+			memcpy(out_buf, in_buf, src_len);
+		else {
+			r = lzo1x_decompress_safe((u8 *) in_buf, src_len,
+						out_buf, &tmp);
+
+			if (r != LZO_E_OK || dst_len != tmp) {
+				error("Compressed data violation");
+				goto exit_2;
+			}
+		}
+
+		if (flush && flush(out_buf, dst_len) != dst_len)
+			goto exit_2;
+		if (output)
+			out_buf += dst_len;
+		if (posp)
+			*posp += src_len + 12;
+
+		in_buf += src_len;
+		in_len -= src_len;
+		if (fill) {
+			/*
+			 * If there happens to still be unused data left in
+			 * in_buf, move it to the beginning of the buffer.
+			 * Use a loop to avoid memmove() dependency.
+			 */
+			if (in_len > 0)
+				for (skip = 0; skip < in_len; ++skip)
+					in_buf_save[skip] = in_buf[skip];
+			in_buf = in_buf_save;
+		}
+	}
+
+	ret = 0;
+exit_2:
+	if (!input)
+		free(in_buf_save);
+exit_1:
+	if (!output)
+		free(out_buf);
+exit:
+	return ret;
+}
+
+#ifdef PREBOOT
+STATIC int INIT __decompress(unsigned char *buf, long len,
+			   long (*fill)(void*, unsigned long),
+			   long (*flush)(void*, unsigned long),
+			   unsigned char *out_buf, long olen,
+			   long *pos,
+			   void (*error)(char *x))
+{
+	return unlzo(buf, len, fill, flush, out_buf, pos, error);
+}
+#endif