runtime: signal stack change broke DragonflyBSD

[bradfitz]

This CL (292558b) broke Dragonfly:

runtime: restore the Go-allocated signal stack in unminit
https://go-review.googlesource.com/c/go/+/81476

I emailed Austin & Ian details of how to access a VM I created.

[bradfitz]

/cc @aclements @ianlancetaylor

[ianlancetaylor]

This most likely has to do with the fact that on DragonFly a newly created thread inherits the alternate signal stack of the creating thread. See the comment in minit in runtime/os_dragonfly.go.

[ianlancetaylor]

Sorry, I was looking at an old source tree due to a complex accident. DragonFly used to work that way, but it's been fixed.

[gopherbot]

Change https://golang.org/cl/83035 mentions this issue: runtime: don't use MAP_STACK on DragonFly in SigStack test