Avoid calling memcpy with NULL pointers #305
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I think adding a branch in |
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Are you concerned about the performance? I have not seen any difference caused by this change. |
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If the objective is to prevent calling if (count) {
data_.a.elements = (GenericValue*)allocator.Malloc(count * sizeof(GenericValue));
std::memcpy(data_.a.elements, values, count * sizeof(GenericValue));
}
else
data_.a.elements = 0;
data_.a.size = data_.a.capacity = count;
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Oh, you're right. |
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PR updated, see 0c5c153. |
According to the C/C++ standards, calling `memcpy(NULL, NULL, 0)` is undefined behaviour. Recent GCC versions may rely on this by optimizing NULL pointer checks more aggressively, see [1]. This patch tries to avoid calling std::memcpy with zero elements. As a side effect, explicitly return NULL when requesting an empty block from MemoryPoolAllocator::Malloc. This may be related to Tencent#301. [1] https://gcc.gnu.org/gcc-4.9/porting_to.html
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miloyip
added a commit
that referenced
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Apr 17, 2015
Avoid calling memcpy with NULL pointers
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I added a test case and also standardize CrtAllocator::Malloc() in 0e8bbe5. |
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Thanks! 👍 |
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According to the C/C++ standards, calling
memcpy(NULL, NULL, 0)is undefined behaviour. Recent GCC versions may rely on this by optimizing NULL pointer checks more aggressively, see [1].This patch tries to avoid calling std::memcpy with zero elements. As a side effect, explicitly return NULL when requesting an empty block from MemoryPoolAllocator::Malloc.
This may be related to #301. Opening the pull-request as requested by @miloyip.
[1] https://gcc.gnu.org/gcc-4.9/porting_to.html