[Core] Improve CowData and Memory metadata alignment.
#87814
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bruvzg
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Tested on:
On 32-bit Linux, I'm getting a few failed Another unrelated note: 32-bit MinGW GCC crash when building with debug symbols on Windows (cross-building is fine), probably symbols are not too big (might be worth adding a note to the compiling page). |
core/os/memory.cpp
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| // Alignment: ↓ max_align_t ↓ uint64_t ↓ max_align_t | ||
| // ┌─────────────────┬──┬────────────────┬──┬───────────... | ||
| // │ uint64_t │░░│ uint64_t │░░│ T[] | ||
| // │ alloc size │░░│ element count │░░│ data | ||
| // └─────────────────┴──┴────────────────┴──┴───────────... | ||
| // Offset: ↑ _size_offset ↑ _elem_offset ↑ _data_offset | ||
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core/templates/cowdata.h
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| @@ -46,7 +46,7 @@ class CharString; | |||
| template <class T, class V> | |||
| class VMap; | |||
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| SAFE_NUMERIC_TYPE_PUN_GUARANTEES(uint64_t) | |||
| static_assert(std::is_trivially_destructible<std::atomic<uint64_t>>::value); | |||
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If this because of the SafeNumeric<uint64_t> around, I'd suggest including this in the set of type-pun guarantees macro in safe_refcount.h.
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It is part of SAFE_NUMERIC_TYPE_PUN_GUARANTEES:
#define SAFE_NUMERIC_TYPE_PUN_GUARANTEES(m_type) \
static_assert(sizeof(SafeNumeric<m_type>) == sizeof(m_type)); \
static_assert(alignof(SafeNumeric<m_type>) == alignof(m_type)); \
static_assert(std::is_trivially_destructible<std::atomic<m_type>>::value);
We take case or sizes and alignment manually (since alignof part is not true on 32-bit platforms), and I have copy-pasted the remaining check here (but I'm not sure if there's any point for checking it for uint64_t at all).
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Needs rebase after #87871. |
bruvzg
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Thanks! |
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Would be good to get a Godot-cpp equivalent fix too |
Will do it soon. |
Fixes #87442
This should not change real memory structure on any platform. But instead of hard-coded values, it is using actual sizes and alignments to allocate and access metadata.