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Differential D26444

Move PLTs to the beginning of amd64 kmods.
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Authored by markj on Sep 15 2020, 6:47 PM.
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jhb
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rS365796: Move PLTs to the beginning of amd64 kernel modules.
Summary

As with .text, the idea is to ensure that executable sections are
segregated from the rest. For some reason, firmware modules end up with
a 16-byte PLT. This wasn't the case before LLVM 11 I believe.

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rS FreeBSD src repository - subversion
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Event Timeline

markj requested review of this revision.Sep 15 2020, 6:47 PM
markj created this revision.
Harbormaster completed remote builds in B33577: Diff 77064.Sep 15 2020, 6:47 PM
markj edited the summary of this revision. (Show Details)Sep 15 2020, 6:51 PM
markj added reviewers: kib, jhb.
kib added a comment.Sep 15 2020, 7:04 PM

Can you show output from readelf -a for that files ? It is very strange to see plt in the result of incremental linking.

markj added a comment.Sep 15 2020, 7:16 PM
In D26444#588245, @kib wrote:

Can you show output from readelf -a for that files ? It is very strange to see plt in the result of incremental linking.

Sure: https://reviews.freebsd.org/P424

This was linked with the patch applied.

kib accepted this revision.Sep 15 2020, 7:38 PM

Hm, I see the same .plt section on stable/12 with clang 10.0.1 as well.

There are two PLT32 relocs, but creating plt for them is not the duty of ld -r. Anyway.

This revision is now accepted and ready to land.Sep 15 2020, 7:38 PM
markj added a comment.Sep 15 2020, 7:59 PM
In D26444#588281, @kib wrote:

Hm, I see the same .plt section on stable/12 with clang 10.0.1 as well.

Huh, I don't remember seeing this. Maybe I last checked when llvm was at version 9.

There are two PLT32 relocs, but creating plt for them is not the duty of ld -r. Anyway.

Indeed. In regular modules there are many PLT32 relocs but no .plt, and I don't see any differences in cc/ld flags.

Closed by commit rS365796: Move PLTs to the beginning of amd64 kernel modules. (authored by markj). · Explain WhySep 16 2020, 1:52 PM
This revision was automatically updated to reflect the committed changes.
markj added a commit: rS365796: Move PLTs to the beginning of amd64 kernel modules..
Herald added a subscriber: imp. · View Herald TranscriptSep 16 2020, 1:52 PM

Revision Contents
Changeset List

PathSize
head/
sys/
conf/
4 lines

Diff 77097

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head/sys/conf/ldscript.kmod.amd64

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