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RISC-V and unaligned memory access #1670

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ccawley2011 opened this issue Feb 16, 2024 · 1 comment
Open

RISC-V and unaligned memory access #1670

ccawley2011 opened this issue Feb 16, 2024 · 1 comment
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@ccawley2011
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The RISC-V chunkset code includes the line uint##elen##_t val = *(uint##elen##_t*)from; as part of the CHUNK_MEMSET_RVV_IMPL, however all the other chunkset implementations use alignment-safe reads here. RISC-V also doesn't define UNALIGNED_OK, and looking at the output from Compiler Explorer shows that both memcpy and __attribute__ ((__packed__, __may_alias__)) read one byte at a time for smaller sizes. Is using unaligned reads intentional here?
@mtl1979
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mtl1979 commented Feb 16, 2024

AFAIK RISC-V traps on unaligned loads and stores, but can handle them in M-mode. In case of reads, it will read more and shift the result to get the correct bytes. In case of unaligned writes, it will write byte by byte.

@nmoinvaz nmoinvaz added the Architecture Architecture specific label Feb 27, 2024
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@nmoinvaz @mtl1979 @ccawley2011