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runtime: initialize extra M for cgo during mstart

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Previously the extra m needed for cgo callbacks was created on the
first callback. This works for cgo, however the cgocallback mechanism
is also borrowed by badsignal which can run before any cgo calls are
made.

Now we initialize the extra M at runtime startup before any signal
handlers are registered, so badsignal cannot be called until the
extra M is ready.

Updates #10207.

Change-Id: Iddda2c80db6dc52d8b60e2b269670fbaa704c7b3
Reviewed-on: https://go-review.googlesource.com/7978
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
This commit is contained in:
David Crawshaw 2015-03-24 09:22:35 -04:00
parent 63f59b6322
commit b8caed823b
3 changed files with 5 additions and 14 deletions
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9
src/runtime/sigqueue.go
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@ -165,14 +165,5 @@ func signal_ignore(s uint32) {
// This runs on a foreign stack, without an m or a g. No stack split.
//go:nosplit
func badsignal(sig uintptr) {
// Some external libraries, for example, OpenBLAS, create worker threads in
// a global constructor. If we're doing cpu profiling, and the SIGPROF signal
// comes to one of the foreign threads before we make our first cgo call, the
// call to cgocallback below will bring down the whole process.
// It's better to miss a few SIGPROF signals than to abort in this case.
// See http://golang.org/issue/9456.
if _SIGPROF != 0 && sig == _SIGPROF && needextram != 0 {
return
}
cgocallback(unsafe.Pointer(funcPC(sigsend)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig))
}