From 5f074f3e192f10c9fade898b9b3b8812e3d83342 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Fri, 5 Apr 2019 18:38:45 -0700 Subject: lib/string.c: implement a basic bcmp A recent optimization in Clang (r355672) lowers comparisons of the return value of memcmp against zero to comparisons of the return value of bcmp against zero. This helps some platforms that implement bcmp more efficiently than memcmp. glibc simply aliases bcmp to memcmp, but an optimized implementation is in the works. This results in linkage failures for all targets with Clang due to the undefined symbol. For now, just implement bcmp as a tailcail to memcmp to unbreak the build. This routine can be further optimized in the future. Other ideas discussed: * A weak alias was discussed, but breaks for architectures that define their own implementations of memcmp since aliases to declarations are not permitted (only definitions). Arch-specific memcmp implementations typically declare memcmp in C headers, but implement them in assembly. * -ffreestanding also is used sporadically throughout the kernel. * -fno-builtin-bcmp doesn't work when doing LTO. Link: https://bugs.llvm.org/show_bug.cgi?id=41035 Link: https://code.woboq.org/userspace/glibc/string/memcmp.c.html#bcmp Link: https://github.com/llvm/llvm-project/commit/8e16d73346f8091461319a7dfc4ddd18eedcff13 Link: https://github.com/ClangBuiltLinux/linux/issues/416 Link: http://lkml.kernel.org/r/20190313211335.165605-1-ndesaulniers@google.com Signed-off-by: Nick Desaulniers Reported-by: Nathan Chancellor Reported-by: Adhemerval Zanella Suggested-by: Arnd Bergmann Suggested-by: James Y Knight Suggested-by: Masahiro Yamada Suggested-by: Nathan Chancellor Suggested-by: Rasmus Villemoes Acked-by: Steven Rostedt (VMware) Reviewed-by: Nathan Chancellor Tested-by: Nathan Chancellor Reviewed-by: Masahiro Yamada Reviewed-by: Andy Shevchenko Cc: David Laight Cc: Rasmus Villemoes Cc: Namhyung Kim Cc: Greg Kroah-Hartman Cc: Alexander Shishkin Cc: Dan Williams Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/string.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'lib') diff --git a/lib/string.c b/lib/string.c index 38e4ca08e757..3ab861c1a857 100644 --- a/lib/string.c +++ b/lib/string.c @@ -866,6 +866,26 @@ __visible int memcmp(const void *cs, const void *ct, size_t count) EXPORT_SYMBOL(memcmp); #endif +#ifndef __HAVE_ARCH_BCMP +/** + * bcmp - returns 0 if and only if the buffers have identical contents. + * @a: pointer to first buffer. + * @b: pointer to second buffer. + * @len: size of buffers. + * + * The sign or magnitude of a non-zero return value has no particular + * meaning, and architectures may implement their own more efficient bcmp(). So + * while this particular implementation is a simple (tail) call to memcmp, do + * not rely on anything but whether the return value is zero or non-zero. + */ +#undef bcmp +int bcmp(const void *a, const void *b, size_t len) +{ + return memcmp(a, b, len); +} +EXPORT_SYMBOL(bcmp); +#endif + #ifndef __HAVE_ARCH_MEMSCAN /** * memscan - Find a character in an area of memory. -- cgit v1.2.3 From b11ed18efa8f3dc58b259b812588317b765b1cfc Mon Sep 17 00:00:00 2001 From: Dave Rodgman Date: Fri, 5 Apr 2019 18:38:58 -0700 Subject: lib/lzo: fix bugs for very short or empty input For very short input data (0 - 1 bytes), lzo-rle was not behaving correctly. Fix this behaviour and update documentation accordingly. For zero-length input, lzo v0 outputs an end-of-stream marker only, which was misinterpreted by lzo-rle as a bitstream version number. Ensure bitstream versions > 0 require a minimum stream length of 5. Also fixes a bug in handling the tail for very short inputs when a bitstream version is present. Link: http://lkml.kernel.org/r/20190326165857.34613-1-dave.rodgman@arm.com Signed-off-by: Dave Rodgman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/lzo.txt | 8 +++++--- lib/lzo/lzo1x_compress.c | 9 ++++++--- lib/lzo/lzo1x_decompress_safe.c | 4 +--- 3 files changed, 12 insertions(+), 9 deletions(-) (limited to 'lib') diff --git a/Documentation/lzo.txt b/Documentation/lzo.txt index f79934225d8d..ca983328976b 100644 --- a/Documentation/lzo.txt +++ b/Documentation/lzo.txt @@ -102,9 +102,11 @@ Byte sequences dictionary which is empty, and that it will always be invalid at this place. - 17 : bitstream version. If the first byte is 17, the next byte - gives the bitstream version (version 1 only). If the first byte - is not 17, the bitstream version is 0. + 17 : bitstream version. If the first byte is 17, and compressed + stream length is at least 5 bytes (length of shortest possible + versioned bitstream), the next byte gives the bitstream version + (version 1 only). + Otherwise, the bitstream version is 0. 18..21 : copy 0..3 literals state = (byte - 17) = 0..3 [ copy literals ] diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c index 4525fb094844..a8ede77afe0d 100644 --- a/lib/lzo/lzo1x_compress.c +++ b/lib/lzo/lzo1x_compress.c @@ -291,13 +291,14 @@ int lzogeneric1x_1_compress(const unsigned char *in, size_t in_len, { const unsigned char *ip = in; unsigned char *op = out; + unsigned char *data_start; size_t l = in_len; size_t t = 0; signed char state_offset = -2; unsigned int m4_max_offset; - // LZO v0 will never write 17 as first byte, - // so this is used to version the bitstream + // LZO v0 will never write 17 as first byte (except for zero-length + // input), so this is used to version the bitstream if (bitstream_version > 0) { *op++ = 17; *op++ = bitstream_version; @@ -306,6 +307,8 @@ int lzogeneric1x_1_compress(const unsigned char *in, size_t in_len, m4_max_offset = M4_MAX_OFFSET_V0; } + data_start = op; + while (l > 20) { size_t ll = l <= (m4_max_offset + 1) ? l : (m4_max_offset + 1); uintptr_t ll_end = (uintptr_t) ip + ll; @@ -324,7 +327,7 @@ int lzogeneric1x_1_compress(const unsigned char *in, size_t in_len, if (t > 0) { const unsigned char *ii = in + in_len - t; - if (op == out && t <= 238) { + if (op == data_start && t <= 238) { *op++ = (17 + t); } else if (t <= 3) { op[state_offset] |= t; diff --git a/lib/lzo/lzo1x_decompress_safe.c b/lib/lzo/lzo1x_decompress_safe.c index 6d2600ea3b55..9e07e9ef1aad 100644 --- a/lib/lzo/lzo1x_decompress_safe.c +++ b/lib/lzo/lzo1x_decompress_safe.c @@ -54,11 +54,9 @@ int lzo1x_decompress_safe(const unsigned char *in, size_t in_len, if (unlikely(in_len < 3)) goto input_overrun; - if (likely(*ip == 17)) { + if (likely(in_len >= 5) && likely(*ip == 17)) { bitstream_version = ip[1]; ip += 2; - if (unlikely(in_len < 5)) - goto input_overrun; } else { bitstream_version = 0; } -- cgit v1.2.3