Yeah, @ianlancetaylor and I were just discussing this. No clue what's going on yet.

I'm pretty sure this must be related to https://golang.org/cl/33142, though I don't see how.

@bcmills

The failure, as seen in

https://build.golang.org/log/17502ae096be2c10fedd81dbb9211e195aba2871
https://build.golang.org/log/415ae3c44929c4e3d54987e18fbe382b6aeac3f1
https://storage.googleapis.com/go-build-log/2f40e962/linux-amd64_a884cd40.log

is that the third and last time that misc/cgo/testcshared/main5.c raises SIGIO, the program crashes. At that point the signal handler is supposed to be the C signal handler that was installed before the shared library was dlopened'd. The C signal handler should have been restored by the call to ResetSIGIO which calls signal.Reset(syscall.SIGIO) which eventually calls sigdisable(SIGIO) which calls setsig(sig, fwdSig[sig]) which should have the effect of setting the signal handler back to the value it had when the shared library was loaded.

CL https://golang.org/cl/33331 mentions this issue.

I don't know for sure that this is fixed, as I was not able to recreate the problem. Optimistically leaving this closed; let's see if the problem recurs.

I saw this a bunch of times on Launchpad builders but haven't seen it since that fix (I have daily builds going now). I'll post here if it reappears.