From 4d0a82170a25464c39522d7190b9fe302045ddb2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 26 Sep 2018 14:39:10 -0400 Subject: fix aliasing-based undefined behavior in string functions use the GNU C may_alias attribute if available, and fallback to naive byte-by-byte loops if __GNUC__ is not defined. this patch has been written to minimize changes so that history remains reviewable; it does not attempt to bring the affected code into a more consistent or elegant form. --- src/string/memccpy.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'src/string/memccpy.c') diff --git a/src/string/memccpy.c b/src/string/memccpy.c index 7c233d5e..f515581c 100644 --- a/src/string/memccpy.c +++ b/src/string/memccpy.c @@ -11,19 +11,22 @@ void *memccpy(void *restrict dest, const void *restrict src, int c, size_t n) { unsigned char *d = dest; const unsigned char *s = src; - size_t *wd, k; - const size_t *ws; c = (unsigned char)c; +#ifdef __GNUC__ + typedef size_t __attribute__((__may_alias__)) word; + word *wd; + const word *ws; if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) { for (; ((uintptr_t)s & ALIGN) && n && (*d=*s)!=c; n--, s++, d++); if ((uintptr_t)s & ALIGN) goto tail; - k = ONES * c; + size_t k = ONES * c; wd=(void *)d; ws=(const void *)s; for (; n>=sizeof(size_t) && !HASZERO(*ws^k); n-=sizeof(size_t), ws++, wd++) *wd = *ws; d=(void *)wd; s=(const void *)ws; } +#endif for (; n && (*d=*s)!=c; n--, s++, d++); tail: if (*s==c) return d+1; -- cgit v1.2.3-70-g09d2