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Differential D23958

[PowerPC64] restrict memcpy/bcopy optimization to POWER ISA >=V2.07
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Authored by alfredo on Mar 4 2020, 5:50 PM.
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luporl
jhibbits
bdragon
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rS358672: [PowerPC64] restrict memcpy/bcopy optimization to POWER ISA >=V2.07
Summary

VSX instructions were added in POWER ISA V2.06 (POWER7), but it requires data to be word-aligned. Such requirement was removed in ISA V2.07B (POWER8).

Since current memcpy/bcopy optimization relies on VSX instructions handling misalignment transparently, and kernel doesn't currently implement an alignment error handler, we should restrict this to ISA V2.07 onwards.

SIGBUS on stxvd2x instruction was reproduced in POWER7+ CPU.

Test Plan

Buildworld and chroot
Installworld and reboot

Diff Detail

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Lint Passed
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Build Status
Buildable 29783
Build 27617: arc lint + arc unit

Event Timeline

alfredo created this revision.Mar 4 2020, 5:50 PM
Harbormaster completed remote builds in B29782: Diff 69165.Mar 4 2020, 5:50 PM
bdragon added inline comments.Mar 4 2020, 5:54 PM
lib/libc/powerpc64/string/bcopy_resolver.c
64–69

Perhaps put a comment here explaining why this was chosen, so nobody's tempted to change it back to PPC_FEATURE_HAS_VSX a couple years down the road when we've forgotten this.

alfredo updated this revision to Diff 69166.Mar 4 2020, 5:54 PM

Added code comments

Harbormaster completed remote builds in B29783: Diff 69166.Mar 4 2020, 5:54 PM
alfredo marked an inline comment as done.Mar 4 2020, 5:55 PM
luporl accepted this revision.Mar 4 2020, 5:57 PM

LGTM

This revision is now accepted and ready to land.Mar 4 2020, 5:57 PM
bdragon accepted this revision.Mar 4 2020, 6:25 PM

Looks fine to me as well.

jhibbits accepted this revision.Mar 4 2020, 8:57 PM
Closed by commit rS358672: [PowerPC64] restrict memcpy/bcopy optimization to POWER ISA >=V2.07 (authored by alfredo). · Explain WhyMar 5 2020, 2:13 PM
This revision was automatically updated to reflect the committed changes.
alfredo added a commit: rS358672: [PowerPC64] restrict memcpy/bcopy optimization to POWER ISA >=V2.07.
Herald added a subscriber: imp. · View Herald TranscriptMar 5 2020, 2:13 PM
alfredo mentioned this in D23969: powerpc/powerpc64: Enforce natural alignment in memcpy.Mar 5 2020, 8:09 PM

Revision Contents
Changeset List

PathSize
lib/
libc/
powerpc64/
string/
7 lines

Diff 69166

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lib/libc/powerpc64/string/bcopy_resolver.c

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