powerpc/powerpc64: Enforce natural alignment in memcpy
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Authored by jhibbits on Mar 5 2020, 2:59 PM.

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Reviewers

luporl
alfredo

Group Reviewers

PowerPC

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rS358688: powerpc/powerpc64: Enforce natural alignment in memcpy

Summary

POWER architecture CPUs (Book-S) require natural alignment for
cache-inhibited storage accesses. Since we can't know the caching model
for a page ahead of time, always enforce natural alignment in memcpy.
This fixes a SIGBUS in X with acceleration enabled on POWER9.

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Build Status

Buildable 29804
Build 27635: arc lint + arc unit

Event Timeline

jhibbits created this revision.Mar 5 2020, 2:59 PM

Harbormaster completed remote builds in B29804: Diff 69219.Mar 5 2020, 2:59 PM

luporl added inline comments.Mar 5 2020, 4:09 PM

lib/libc/powerpc64/string/memcpy.S
61	You also need to check if len (r5) is 0 and exit, because .Lcopy_remaining_fix_index_byte doesn't handle this case.

luporl added inline comments.Mar 5 2020, 4:10 PM

lib/libc/powerpc64/string/memcpy.S
61	Sorry, I missed the cmpdi %r5, 0 above, so forget my previous comment.

I tested this patch with D23958/r358672 reverted. This solution makes optimized memcpy/bcopy code viable again on POWER7. It slows down some cases but it's a gain in overal, I think.

This revision is now accepted and ready to land.Mar 5 2020, 8:09 PM

Closed by commit rS358688: powerpc/powerpc64: Enforce natural alignment in memcpy (authored by jhibbits). · Explain WhyMar 6 2020, 1:45 AM

This revision was automatically updated to reflect the committed changes.

jhibbits added a commit: rS358688: powerpc/powerpc64: Enforce natural alignment in memcpy.

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