diff options
Diffstat (limited to 'lib/xalloc-oversized.h')
| -rw-r--r-- | lib/xalloc-oversized.h | 51 |
1 files changed, 36 insertions, 15 deletions
diff --git a/lib/xalloc-oversized.h b/lib/xalloc-oversized.h index d81a8471d37..503bb37801b 100644 --- a/lib/xalloc-oversized.h +++ b/lib/xalloc-oversized.h @@ -19,29 +19,50 @@ #define XALLOC_OVERSIZED_H_ #include <stddef.h> +#include <stdint.h> +/* Default for (non-Clang) compilers that lack __has_builtin. */ #ifndef __has_builtin # define __has_builtin(x) 0 #endif -/* 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. - +/* 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. */ -#if 5 <= __GNUC__ || __has_builtin (__builtin_mul_overflow) -# define xalloc_oversized(n, s) \ - ({ size_t __xalloc_size; __builtin_mul_overflow (n, s, &__xalloc_size); }) + 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) \ + __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) \ - ((size_t) (sizeof (ptrdiff_t) <= sizeof (size_t) ? -1 : -2) / (s) < (n)) + (__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_ */ |