runtime: initialize extra M for cgo during mstart

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>

1 files changed, 0 insertions, 9 deletions

diff --git a/src/runtime/sigqueue.go b/src/runtime/sigqueue.go
index df3c9c0e61..9cfe2592db 100644
--- a/src/runtime/sigqueue.go
+++ b/src/runtime/sigqueue.go
@@ -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))
 }