From 6be9d752142a03830e4202bd73f2765510ff9314 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Tue, 5 Apr 2022 16:04:09 -0700 Subject: libbacktrace: don't skip initial aligned byte in uncompressed block Patch from Rui Ueyama, who says: libbacktrace occasionally fails to decompress compressed debug info even though the sections contain valid zlib streams. The cause of the issue is an off-by-one error. If a zlib data block is a plain data (uncompressed data), the next two bytes contain the size of the block. These two bytes value is byte- aligned, so if we read-ahead more than 8 bits, we need to unread it. So, the correct condition to determine whether or not we need to unread a byte is bits >= 8 and not bits > 8. Due to this error, if the last read bits happened to end at a byte boundary, the next byte would be skipped. That caused the decompression failure. This bug was originally reported against the mold linker. rui314/mold#402 * elf.c (elf_zlib_inflate): Don't skip initial aligned byte in uncompressed block. --- libbacktrace/elf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'libbacktrace') diff --git a/libbacktrace/elf.c b/libbacktrace/elf.c index 5c7c21a8da7..8b82dd45875 100644 --- a/libbacktrace/elf.c +++ b/libbacktrace/elf.c @@ -1796,7 +1796,7 @@ elf_zlib_inflate (const unsigned char *pin, size_t sin, uint16_t *zdebug_table, /* An uncompressed block. */ /* If we've read ahead more than a byte, back up. */ - while (bits > 8) + while (bits >= 8) { --pin; bits -= 8; -- cgit v1.2.3