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runtime: morestack_noctxt missing SPWRITE, causes "traceback stuck" assert [1.19 backport] #54675

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gopherbot opened this issue Aug 25, 2022 · 4 comments
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runtime: morestack_noctxt missing SPWRITE, causes "traceback stuck" assert [1.19 backport] #54675

gopherbot opened this issue Aug 25, 2022 · 4 comments
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CherryPickApproved Used during the release process for point releases compiler/runtime Issues related to the Go compiler and/or runtime. FrozenDueToAge
Milestone
Go1.19.1

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@gopherbot
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@cherrymui requested issue #54332 to be considered for backport to the next 1.19 minor release.

@gopherbot please backport this to previous releases. This may cause a runtime crash. Thanks.
@gopherbot gopherbot added the CherryPickCandidate Used during the release process for point releases label Aug 25, 2022
@gopherbot gopherbot mentioned this issue Aug 25, 2022
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@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Aug 25, 2022
@gopherbot gopherbot added this to the Go1.19.1 milestone Aug 25, 2022
@gopherbot
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Change https://go.dev/cl/425615 mentions this issue: [release-branch.go1.19] runtime: mark morestack_noctxt SPWRITE on LR architectures

@heschi heschi added the CherryPickApproved Used during the release process for point releases label Aug 31, 2022
@gopherbot gopherbot removed the CherryPickCandidate Used during the release process for point releases label Aug 31, 2022
gopherbot pushed a commit that referenced this issue Aug 31, 2022
@cherrymui @heschi
[release-branch.go1.19] runtime: mark morestack_noctxt SPWRITE on LR …
0bba4d2 
…architectures

On LR architectures, morestack (and morestack_noctxt) are called
with a special calling convention, where the caller doesn't save
LR on stack but passes it as a register, which morestack will save
to g.sched.lr. The stack unwinder currently doesn't understand it,
and would fail to unwind from it. morestack already writes SP (as
it switches stack), but morestack_noctxt (which tailcalls
morestack) doesn't. If a profiling signal lands right in
morestack_noctxt, the unwinder will try to unwind the stack and
go off, and possibly crash.

Marking morestack_noctxt SPWRITE stops the unwinding.

Ideally we could teach the unwinder about the special calling
convention, or change the calling convention to be less special
(so the unwinder doesn't need to fetch a register from the signal
context). This is a stop-gap solution, to stop the unwinder from
crashing.

Updates #54332.
Fixes #54675.

Change-Id: I75295f2e27ddcf05f1ea0b541aedcb9000ae7576
Reviewed-on: https://go-review.googlesource.com/c/go/+/425396
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
(cherry picked from commit e4be2ac)
Reviewed-on: https://go-review.googlesource.com/c/go/+/425615
@gopherbot
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Closed by merging 0bba4d2 to release-branch.go1.19.

bradfitz pushed a commit to tailscale/go that referenced this issue Sep 8, 2022
@cherrymui @bradfitz
[release-branch.go1.19] runtime: mark morestack_noctxt SPWRITE on LR …
9d417a5 
…architectures

On LR architectures, morestack (and morestack_noctxt) are called
with a special calling convention, where the caller doesn't save
LR on stack but passes it as a register, which morestack will save
to g.sched.lr. The stack unwinder currently doesn't understand it,
and would fail to unwind from it. morestack already writes SP (as
it switches stack), but morestack_noctxt (which tailcalls
morestack) doesn't. If a profiling signal lands right in
morestack_noctxt, the unwinder will try to unwind the stack and
go off, and possibly crash.

Marking morestack_noctxt SPWRITE stops the unwinding.

Ideally we could teach the unwinder about the special calling
convention, or change the calling convention to be less special
(so the unwinder doesn't need to fetch a register from the signal
context). This is a stop-gap solution, to stop the unwinder from
crashing.

Updates golang#54332.
Fixes golang#54675.

Change-Id: I75295f2e27ddcf05f1ea0b541aedcb9000ae7576
Reviewed-on: https://go-review.googlesource.com/c/go/+/425396
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
(cherry picked from commit e4be2ac)
Reviewed-on: https://go-review.googlesource.com/c/go/+/425615
@lizthegrey
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Backport confirmed working and stable in 1.19.1

@cherrymui
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Thanks @lizthegrey for confirming! This is great.

@golang golang locked and limited conversation to collaborators Sep 16, 2023
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