vabackend: fix alignment of codecs #72
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Making the `NVCodec` structs maximally aligned was an erroneous move because the gcc may increase the alignment which can lead to undesirable behaviour (e.g. elFarto#71). In the aforementioned case the size of the struct was 496 bytes, which was properly aligned to the maximum alignment (`__BIGGEST_ALIGNMENT__`) on the platform (16 bytes - x86-64), but gcc chose to align the objects at a 32 byte boundary, which resulted in 16 bytes of padding between each element that was not accounted for at runtime. Specifying the alignment on the object itself and not the type prevents gcc from increasing the alignment. See: https://lore.kernel.org/lkml/[email protected]/ Fixes: 73ddb63 ("vabackend: make NVCodec struct aligned")
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Sorry again, I hope this will be last installment of the alignment saga. |
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Thanks for the patch! Let's hope this fixes it once and for all. |
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Making the
NVCodecstructs maximally aligned was an erroneous move because the gcc may increase the alignment which can lead to undesirable behaviour (e.g. #71).In the aforementioned case the size of the struct was 496 bytes, which was properly aligned to the maximum alignment (
__BIGGEST_ALIGNMENT__) on the platform (16 bytes - x86-64), but gcc chose to align the objects at a 32 byte boundary, which resulted in 16 bytes of padding between each element that was not accounted for at runtime.Specifying the alignment on the object itself and not the type prevents gcc from increasing the alignment.
See: https://lore.kernel.org/lkml/[email protected]/
Fixes: 73ddb63 ("vabackend: make NVCodec struct aligned")