runtime: unify handling of alternate signal stack

Change all Unix systems to use stackt for the alternate signal
stack (some were using sigaltstackt). Add OS-specific setSignalstackSP
function to handle different types for ss_sp field, and unify all
OS-specific signalstack functions into one. Unify handling of alternate
signal stack in OS-specific minit and sigtrampgo functions via new
functions minitSignalstack and setGsignalStack.

Change-Id: Idc316dc69b1dd725717acdf61a1cd8b9f33ed174
Reviewed-on: https://go-review.googlesource.com/29757
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 4 insertions, 26 deletions

diff --git a/src/runtime/os_openbsd.go b/src/runtime/os_openbsd.go
index 375c100aec..714416fa5b 100644
--- a/src/runtime/os_openbsd.go
+++ b/src/runtime/os_openbsd.go
@@ -218,22 +218,7 @@ func minit() {
 	// m.procid is a uint64, but tfork writes an int32. Fix it up.
 	_g_.m.procid = uint64(*(*int32)(unsafe.Pointer(&_g_.m.procid)))
 
-	// Initialize signal handling
-	var st stackt
-	sigaltstack(nil, &st)
-	if st.ss_flags&_SS_DISABLE != 0 {
-		signalstack(&_g_.m.gsignal.stack)
-		_g_.m.newSigstack = true
-	} else {
-		// Use existing signal stack.
-		stsp := uintptr(unsafe.Pointer(st.ss_sp))
-		_g_.m.gsignal.stack.lo = stsp
-		_g_.m.gsignal.stack.hi = stsp + st.ss_size
-		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
-		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
-		_g_.m.gsignal.stackAlloc = st.ss_size
-		_g_.m.newSigstack = false
-	}
+	minitSignalStack()
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -298,17 +283,10 @@ func getsig(i int32) uintptr {
 	return sa.sa_sigaction
 }
 
+// setSignaltstackSP sets the ss_sp field of a stackt.
 //go:nosplit
-func signalstack(s *stack) {
-	var st stackt
-	if s == nil {
-		st.ss_flags = _SS_DISABLE
-	} else {
-		st.ss_sp = s.lo
-		st.ss_size = s.hi - s.lo
-		st.ss_flags = 0
-	}
-	sigaltstack(&st, nil)
+func setSignalstackSP(s *stackt, sp uintptr) {
+	s.ss_sp = sp
 }
 
 //go:nosplit