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runtime: next release of OpenBSD requires MAP_STACK for stacks #26142

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aclements opened this issue Jun 29, 2018 · 3 comments
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runtime: next release of OpenBSD requires MAP_STACK for stacks #26142

aclements opened this issue Jun 29, 2018 · 3 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. OS-OpenBSD
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Go1.11

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@aclements
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As announced in http://openbsd-archive.7691.n7.nabble.com/stack-register-checking-td338238.html, the upcoming release of OpenBSD is going to start requiring that the SP points to memory that was mapped with MAP_STACK on system call entry, traps, and when switching to the alternate signal stack. This breaks with the current version of Go because we don't map any memory MAP_STACK.

Fixing this is somewhat tricky given how tightly we allocate stacks and that they are interwoven with heap memory. However, they're not interwoven below page granularity, so it should be possible to fix this by remapping memory whenever a span transitions to or from being used to allocate stacks.
@gopherbot
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Change https://golang.org/cl/121657 mentions this issue: runtime: remap stack spans with MAP_STACK on OpenBSD

@aclements aclements added this to the Go1.11 milestone Jun 29, 2018
@4a6f656c
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4a6f656c commented Jul 9, 2018

Unfortunately this is not quite fixed - it still fails on OpenBSD -current (what will become 6.4) as soon as a new thread is created:

$ ./all.bash
Building Go cmd/dist using /home/joel/src/go1.4.
Building Go toolchain1 using /home/joel/src/go1.4.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
go tool dist: FAILED: /home/joel/src/go/pkg/tool/openbsd_amd64/go_bootstrap install -gcflags=all= -ldflags=all= -a -i cmd/asm cmd/cgo cmd/compile cmd/link: signal: segmentation fault (core dumped)

I'll send a change to fix this.

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Change https://golang.org/cl/122735 mentions this issue: runtime: correct new thread stack for openbsd MAP_STACK

@aclements aclements reopened this Jul 9, 2018
@ianlancetaylor ianlancetaylor added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Jul 10, 2018
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