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cmd/compile: R12 can be clobbered for write barrier call on PPC64 [1.15 backport] #40868

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gopherbot opened this issue Aug 18, 2020 · 4 comments
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cmd/compile: R12 can be clobbered for write barrier call on PPC64 [1.15 backport] #40868

gopherbot opened this issue Aug 18, 2020 · 4 comments
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CherryPickApproved Used during the release process for point releases FrozenDueToAge
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Go1.15.2

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@gopherbot
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@cherrymui requested issue #40851 to be considered for backport to the next 1.15 minor release.

@gopherbot please consider backporting this to Go 1.15. Thanks.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Aug 18, 2020
@gopherbot gopherbot mentioned this issue Aug 18, 2020
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@gopherbot gopherbot added this to the Go1.15.1 milestone Aug 18, 2020
@cherrymui
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(Copied from the original issue)
I think we may want to back port, as this could cause runtime crash or data corruption without workaround.

@gopherbot
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Change https://golang.org/cl/249019 mentions this issue: [release-branch.go1.15] cmd/compile, runtime: mark R12 clobbered for write barrier call on PPC64

@dmitshur dmitshur modified the milestones: Go1.15.1, Go1.15.2 Sep 1, 2020
@dmitshur
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dmitshur commented Sep 2, 2020

Approving per discussion in a release meeting. This backport applies to both 1.15 (this issue) and 1.14 (#40938).

@dmitshur dmitshur mentioned this issue Sep 2, 2020
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@dmitshur dmitshur added CherryPickApproved Used during the release process for point releases and removed CherryPickCandidate Used during the release process for point releases labels Sep 2, 2020
@gopherbot
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Closed by merging f50cde9 to release-branch.go1.15.

gopherbot pushed a commit that referenced this issue Sep 3, 2020
@cherrymui @dmitshur
[release-branch.go1.15] cmd/compile, runtime: mark R12 clobbered for …
f50cde9 
…write barrier call on PPC64

When external linking, for large binaries, the external linker
may insert a trampoline for the write barrier call, which looks

0000000005a98cc8 <__long_branch_runtime.gcWriteBarrier>:
 5a98cc8:       86 01 82 3d     addis   r12,r2,390
 5a98ccc:       d8 bd 8c e9     ld      r12,-16936(r12)
 5a98cd0:       a6 03 89 7d     mtctr   r12
 5a98cd4:       20 04 80 4e     bctr

It clobbers R12 (and CTR, which is never live across a call).

As at compile time we don't know whether the binary is big and
what link mode will be used, I think we need to mark R12 as
clobbered for write barrier call. For extra safety (future-proof)
we mark caller-saved register that cannot be used for function
arguments, which includes R11, as potentially clobbered as well.

Updates #40851.
Fixes #40868.

Change-Id: Iedd901c5072f1127cc59b0a48cfeb4aaec81b519
Reviewed-on: https://go-review.googlesource.com/c/go/+/248917
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
(cherry picked from commit b58d297)
Reviewed-on: https://go-review.googlesource.com/c/go/+/249019
claucece pushed a commit to claucece/go that referenced this issue Oct 22, 2020
@cherrymui @claucece
[release-branch.go1.15] cmd/compile, runtime: mark R12 clobbered for …
d22de4b 
…write barrier call on PPC64

When external linking, for large binaries, the external linker
may insert a trampoline for the write barrier call, which looks

0000000005a98cc8 <__long_branch_runtime.gcWriteBarrier>:
 5a98cc8:       86 01 82 3d     addis   r12,r2,390
 5a98ccc:       d8 bd 8c e9     ld      r12,-16936(r12)
 5a98cd0:       a6 03 89 7d     mtctr   r12
 5a98cd4:       20 04 80 4e     bctr

It clobbers R12 (and CTR, which is never live across a call).

As at compile time we don't know whether the binary is big and
what link mode will be used, I think we need to mark R12 as
clobbered for write barrier call. For extra safety (future-proof)
we mark caller-saved register that cannot be used for function
arguments, which includes R11, as potentially clobbered as well.

Updates golang#40851.
Fixes golang#40868.

Change-Id: Iedd901c5072f1127cc59b0a48cfeb4aaec81b519
Reviewed-on: https://go-review.googlesource.com/c/go/+/248917
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
(cherry picked from commit b58d297)
Reviewed-on: https://go-review.googlesource.com/c/go/+/249019
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