Do not use b.cs instruction to jump to cerror
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Authored by kan on Apr 7 2017, 3:28 PM.

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Reviewers

andrew
emaste

Group Reviewers

arm64

Commits

rS316624: Do not use b.cs instruction to jump to cerror.

Summary

The conditional jump can only be performed tp targets up to 1MB in
either direction and does not work too well when linker places cerror
further that that from the caller. In that case linker will complain
about relocation overflows.

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Repository

rS FreeBSD src repository - subversion

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Build Status

Buildable 8583
Build 8897: CI src build	Jenkins

Event Timeline

kan created this revision.Apr 7 2017, 3:28 PM

Herald added a subscriber: imp. · View Herald TranscriptApr 7 2017, 3:28 PM

Can you add a comment to point out why we use the b.cs ; ret ; b sequence.

Harbormaster failed remote builds in B8583: Diff 27179!Apr 7 2017, 3:32 PM

imp added inline comments.Apr 7 2017, 3:34 PM

lib/libc/aarch64/SYS.h
54	why not use b cerror directly?

andrew added inline comments.Apr 7 2017, 3:38 PM

lib/libc/aarch64/SYS.h
54	How? We still need to check the process state as that's how syscalls signal failure.

This LGTM with @andrew's note addressed, probably just make a comment out of a short version of the explanation that's in the Phabricator summary?

Also, with luck a future version of the linker will insert a thunk by itself when necessary, and we could then revert this.

This revision is now accepted and ready to land.Apr 7 2017, 3:54 PM

emaste added a child revision: D10310: do not require binutils port if using lld as ld.Apr 7 2017, 6:33 PM

Closed by commit rS316624: Do not use b.cs instruction to jump to cerror. (authored by kan). · Explain WhyApr 7 2017, 10:58 PM

This revision was automatically updated to reflect the committed changes.

Revision Contents
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lib/

libc/

aarch64/

SYS.h

6 lines

Diff 27179

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Do not use b.cs instruction to jump to cerrorClosedPublicActions