From 8ea0ba7dd03e500a53f96cea855aa2993882652c Mon Sep 17 00:00:00 2001 From: Kir Kolyshkin Date: Fri, 27 Jan 2017 19:01:00 +0300 Subject: [PATCH] string.h: fix memset over-optimization with clang We found a weird case of parasite code dying of SIGSEGV when clang is used as a compiler (see [1] for more details). Apparently, it was caused by clang optimizing our builtin_memset() by inserting a call to memset(). It is a valid compiler optimization, aside from the fact that in our code memset() is defined as a weak alias to builtin_memset(), which of course lead to infinite recursion and stack growth. This might be a bug in compiler, but there are ways to avoid it: 1. Rewrite builtin_memset() in asm (note it needs to be done for every architecture supported). 2. Disable compiler optimizations for this code (say, by using -O0). 3. Declare the pointer inside builtin_memcpy() as volatile. The last approach looks more appealing -- mostly for being simple. [1] https://github.com/xemul/criu/issues/279 travis-ci: success for string.h: fix memset over-optimization with clang Cc: Andrei Vagin Cc: Dmitry Safonov Cc: Cyrill Gorcunov Signed-off-by: Kir Kolyshkin Acked-by: Cyrill Gorcunov Signed-off-by: Pavel Emelyanov --- criu/include/asm-generic/string.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/criu/include/asm-generic/string.h b/criu/include/asm-generic/string.h index ff91968a0..6e0f659af 100644 --- a/criu/include/asm-generic/string.h +++ b/criu/include/asm-generic/string.h @@ -65,7 +65,7 @@ static always_inline int builtin_strncmp(const char *cs, const char *ct, size_t #ifndef HAS_BUILTIN_MEMSET static __maybe_unused void *builtin_memset(void *s, const int c, size_t count) { - char *dest = s; + volatile char *dest = s; size_t i = 0; while (i < count)