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Use checked unsigned multiplication extension of GCC/Clang

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Most processors have carry flags which they set on addition overflow, so
it is a good idea to access them whenever possible. Most of them also
have widening multiply instructions that can be used to detect overflow
of the non-widening version. Both GCC and Clang offer a way to detect an
overflow for security critical applications.

Reference:
  https://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins
This commit is contained in:
Jim Huang 2019-07-07 12:56:40 +08:00
parent 49ceb4d018
commit afd981d008
1 changed files with 11 additions and 0 deletions
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11
include/mimalloc-internal.h
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@ -109,6 +109,9 @@ bool _mi_page_is_valid(mi_page_t* page);
#define mi_likely(x) (x)
#endif
#ifndef __has_builtin
#define __has_builtin(x) 0
#endif
#if defined(_MSC_VER)
#define mi_decl_noinline __declspec(noinline)
@ -141,9 +144,17 @@ bool _mi_page_is_valid(mi_page_t* page);
// Overflow detecting multiply
#define MI_MUL_NO_OVERFLOW ((size_t)1 << (4*sizeof(size_t))) // sqrt(SIZE_MAX)
static inline bool mi_mul_overflow(size_t size, size_t count, size_t* total) {
#if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
#if (MI_INTPTR_SIZE == 4)
return __builtin_umul_overflow(size, count, total);
#else
return __builtin_umull_overflow(size, count, total);
#endif
#else /* __builtin_umul_overflow is unavailable */
*total = size * count;
return ((size >= MI_MUL_NO_OVERFLOW || count >= MI_MUL_NO_OVERFLOW)
&& size > 0 && (SIZE_MAX / size) < count);
#endif
}
// Align a byte size to a size in _machine words_,