From 4d0a82170a25464c39522d7190b9fe302045ddb2 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Wed, 26 Sep 2018 14:39:10 -0400 Subject: [PATCH] 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 ++++++--- src/string/memchr.c | 8 ++++++-- src/string/memmove.c | 8 +++++++- src/string/stpcpy.c | 8 +++++--- src/string/stpncpy.c | 8 +++++--- src/string/strchrnul.c | 11 +++++++---- src/string/strlcpy.c | 5 ++++- src/string/strlen.c | 8 ++++++-- 8 files changed, 46 insertions(+), 19 deletions(-) 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; diff --git a/src/string/memchr.c b/src/string/memchr.c index 4daff7bb..65f0d789 100644 --- a/src/string/memchr.c +++ b/src/string/memchr.c @@ -12,12 +12,16 @@ void *memchr(const void *src, int c, size_t n) { const unsigned char *s = src; c = (unsigned char)c; +#ifdef __GNUC__ for (; ((uintptr_t)s & ALIGN) && n && *s != c; s++, n--); if (n && *s != c) { - const size_t *w; + typedef size_t __attribute__((__may_alias__)) word; + const word *w; size_t k = ONES * c; for (w = (const void *)s; n>=SS && !HASZERO(*w^k); w++, n-=SS); - for (s = (const void *)w; n && *s != c; s++, n--); + s = (const void *)w; } +#endif + for (; n && *s != c; s++, n--); return n ? (void *)s : 0; } diff --git a/src/string/memmove.c b/src/string/memmove.c index f225bb30..5dc9cdb9 100644 --- a/src/string/memmove.c +++ b/src/string/memmove.c @@ -1,8 +1,10 @@ #include #include -#define WT size_t +#ifdef __GNUC__ +typedef __attribute__((__may_alias__)) size_t WT; #define WS (sizeof(WT)) +#endif void *memmove(void *dest, const void *src, size_t n) { @@ -13,6 +15,7 @@ void *memmove(void *dest, const void *src, size_t n) if ((uintptr_t)s-(uintptr_t)d-n <= -2*n) return memcpy(d, s, n); if (d=WS; n-=WS, d+=WS, s+=WS) *(WT *)d = *(WT *)s; } +#endif for (; n; n--) *d++ = *s++; } else { +#ifdef __GNUC__ if ((uintptr_t)s % WS == (uintptr_t)d % WS) { while ((uintptr_t)(d+n) % WS) { if (!n--) return dest; @@ -29,6 +34,7 @@ void *memmove(void *dest, const void *src, size_t n) } while (n>=WS) n-=WS, *(WT *)(d+n) = *(WT *)(s+n); } +#endif while (n) n--, d[n] = s[n]; } diff --git a/src/string/stpcpy.c b/src/string/stpcpy.c index 54cf9ca5..4db46a9e 100644 --- a/src/string/stpcpy.c +++ b/src/string/stpcpy.c @@ -9,9 +9,10 @@ char *__stpcpy(char *restrict d, const char *restrict s) { - size_t *wd; - const size_t *ws; - +#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; s++, d++) if (!(*d=*s)) return d; @@ -19,6 +20,7 @@ char *__stpcpy(char *restrict d, const char *restrict s) for (; !HASZERO(*ws); *wd++ = *ws++); d=(void *)wd; s=(const void *)ws; } +#endif for (; (*d=*s); s++, d++); return d; diff --git a/src/string/stpncpy.c b/src/string/stpncpy.c index d6d92ffc..f57fa6b7 100644 --- a/src/string/stpncpy.c +++ b/src/string/stpncpy.c @@ -9,9 +9,10 @@ char *__stpncpy(char *restrict d, const char *restrict s, size_t n) { - size_t *wd; - const size_t *ws; - +#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); n--, s++, d++); if (!n || !*s) goto tail; @@ -20,6 +21,7 @@ char *__stpncpy(char *restrict d, const char *restrict s, size_t n) n-=sizeof(size_t), ws++, wd++) *wd = *ws; d=(void *)wd; s=(const void *)ws; } +#endif for (; n && (*d=*s); n--, s++, d++); tail: memset(d, 0, n); diff --git a/src/string/strchrnul.c b/src/string/strchrnul.c index f2b9ae11..39e2635b 100644 --- a/src/string/strchrnul.c +++ b/src/string/strchrnul.c @@ -9,16 +9,19 @@ char *__strchrnul(const char *s, int c) { - size_t *w, k; - c = (unsigned char)c; if (!c) return (char *)s + strlen(s); +#ifdef __GNUC__ + typedef size_t __attribute__((__may_alias__)) word; + const word *w; for (; (uintptr_t)s % ALIGN; s++) if (!*s || *(unsigned char *)s == c) return (char *)s; - k = ONES * c; + size_t k = ONES * c; for (w = (void *)s; !HASZERO(*w) && !HASZERO(*w^k); w++); - for (s = (void *)w; *s && *(unsigned char *)s != c; s++); + s = (void *)w; +#endif + for (; *s && *(unsigned char *)s != c; s++); return (char *)s; } diff --git a/src/string/strlcpy.c b/src/string/strlcpy.c index dcb22f6e..ffa0b0b0 100644 --- a/src/string/strlcpy.c +++ b/src/string/strlcpy.c @@ -12,9 +12,11 @@ size_t strlcpy(char *d, const char *s, size_t n) { char *d0 = d; size_t *wd; - const size_t *ws; if (!n--) goto finish; +#ifdef __GNUC__ + typedef size_t __attribute__((__may_alias__)) word; + const word *ws; if (((uintptr_t)s & ALIGN) == ((uintptr_t)d & ALIGN)) { for (; ((uintptr_t)s & ALIGN) && n && (*d=*s); n--, s++, d++); if (n && *s) { @@ -24,6 +26,7 @@ size_t strlcpy(char *d, const char *s, size_t n) d=(void *)wd; s=(const void *)ws; } } +#endif for (; n && (*d=*s); n--, s++, d++); *d = 0; finish: diff --git a/src/string/strlen.c b/src/string/strlen.c index 929ddcbc..309990f0 100644 --- a/src/string/strlen.c +++ b/src/string/strlen.c @@ -10,9 +10,13 @@ size_t strlen(const char *s) { const char *a = s; - const size_t *w; +#ifdef __GNUC__ + typedef size_t __attribute__((__may_alias__)) word; + const word *w; for (; (uintptr_t)s % ALIGN; s++) if (!*s) return s-a; for (w = (const void *)s; !HASZERO(*w); w++); - for (s = (const void *)w; *s; s++); + s = (const void *)w; +#endif + for (; *s; s++); return s-a; } -- 2.25.1