bpo-27987: align PyGC_Head to alignof(long double) explicitly#13336
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methane wants to merge 1 commit intopython:masterfrom
Closed
bpo-27987: align PyGC_Head to alignof(long double) explicitly#13336methane wants to merge 1 commit intopython:masterfrom
methane wants to merge 1 commit intopython:masterfrom
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vstinner
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May 15, 2019
| // Lowest two bits are used for flags documented later. | ||
| uintptr_t prev; | ||
| } _gc; | ||
| long double _dummy; /* for worst alignment */ |
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Can you please elaborate the comment? Add "bpo-27987" and explain that x64-64 ABI requires to align on 16 bytes.
Do you have to align to 16 bytes on x86 (32-bit) as well?
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Oh! I forgot about 32bit platform.
I thought this PR does nothing, but it makes PyGC_Head to 16 bytes from 8 bytes on x86 platform.
Maybe, we can use __attribute__ ((aligned)) if compiler is GCC or clang.
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Said differently, it doesn't change PyGC_Head size on 64-bit system, right? Does it change the size on 32-bit system? Correctness matters more than code beauty here ;-) |
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PyGC_Head consists two uintptr_t variables so it is aligned to 16 byte
on amd64 platform already.
This commit makes this alignment more explicit, although make code
bit ugly.
https://bugs.python.org/issue27987