diff options
Diffstat (limited to 'lib/xalloc-oversized.h')
| -rw-r--r-- | lib/xalloc-oversized.h | 58 |
1 files changed, 44 insertions, 14 deletions
diff --git a/lib/xalloc-oversized.h b/lib/xalloc-oversized.h index ad777d8..503bb37 100644 --- a/lib/xalloc-oversized.h +++ b/lib/xalloc-oversized.h @@ -1,6 +1,6 @@ /* xalloc-oversized.h -- memory allocation size checking - Copyright (C) 1990-2000, 2003-2004, 2006-2012 Free Software Foundation, Inc. + Copyright (C) 1990-2000, 2003-2004, 2006-2016 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -16,23 +16,53 @@ along with this program. If not, see <http://www.gnu.org/licenses/>. */ #ifndef XALLOC_OVERSIZED_H_ -# define XALLOC_OVERSIZED_H_ +#define XALLOC_OVERSIZED_H_ -# include <stddef.h> +#include <stddef.h> +#include <stdint.h> -/* Return 1 if an array of N objects, each of size S, cannot exist due - to size arithmetic overflow. S must be positive and N must be - nonnegative. This is a macro, not a function, so that it - works correctly even when SIZE_MAX < N. +/* Default for (non-Clang) compilers that lack __has_builtin. */ +#ifndef __has_builtin +# define __has_builtin(x) 0 +#endif +/* True if N * S would overflow in a size_t calculation, + or would generate a value larger than PTRDIFF_MAX. + This expands to a constant expression if N and S are both constants. By gnulib convention, SIZE_MAX represents overflow in size - calculations, so the conservative dividend to use here is - SIZE_MAX - 1, since SIZE_MAX might represent an overflowed value. - However, malloc (SIZE_MAX) fails on all known hosts where - sizeof (ptrdiff_t) <= sizeof (size_t), so do not bother to test for - exactly-SIZE_MAX allocations on such hosts; this avoids a test and - branch when S is known to be 1. */ + calculations, so the conservative size_t-based dividend to use here + is SIZE_MAX - 1. */ +#define __xalloc_oversized(n, s) \ + ((size_t) (PTRDIFF_MAX < SIZE_MAX ? PTRDIFF_MAX : SIZE_MAX - 1) / (s) < (n)) + +#if PTRDIFF_MAX < SIZE_MAX +typedef ptrdiff_t __xalloc_count_type; +#else +typedef size_t __xalloc_count_type; +#endif + +/* Return 1 if an array of N objects, each of size S, cannot exist + reliably due to size or ptrdiff_t arithmetic overflow. S must be + positive and N must be nonnegative. This is a macro, not a + function, so that it works correctly even when SIZE_MAX < N. */ + +#if 7 <= __GNUC__ || __has_builtin (__builtin_add_overflow_p) # define xalloc_oversized(n, s) \ - ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n)) + __builtin_mul_overflow_p (n, s, (__xalloc_count_type) 1) +#elif ((5 <= __GNUC__ \ + || (__has_builtin (__builtin_mul_overflow) \ + && __has_builtin (__builtin_constant_p))) \ + && !__STRICT_ANSI__) +# define xalloc_oversized(n, s) \ + (__builtin_constant_p (n) && __builtin_constant_p (s) \ + ? __xalloc_oversized (n, s) \ + : ({ __xalloc_count_type __xalloc_count; \ + __builtin_mul_overflow (n, s, &__xalloc_count); })) + +/* Other compilers use integer division; this may be slower but is + more portable. */ +#else +# define xalloc_oversized(n, s) __xalloc_oversized (n, s) +#endif #endif /* !XALLOC_OVERSIZED_H_ */ |