runtime: use a proper type, sigset, for m.sigmask

Replace the cross platform but unsafe [4]uintptr type with a OS
specific type, sigset. Most OSes already define sigset, and this
change defines a suitable sigset for the OSes that don't (darwin,
openbsd). The OSes that don't use m.sigmask (windows, plan9, nacl)
now defines sigset as the empty type, struct{}.

The gain is strongly typed access to m.sigmask, saving a dynamic
size sanity check and unsafe.Pointer casting. Also, some storage is
saved for each M, since [4]uinptr was conservative for most OSes.

The cost is that OSes that don't need m.sigmask has to define sigset.

completes ./all.bash with GOOS linux, on amd64
completes ./make.bash with GOOSes openbsd, android, plan9, windows,
darwin, solaris, netbsd, freebsd, dragonfly, all amd64.

With GOOS=nacl ./make.bash failed with a seemingly unrelated error.

R=go1.7

Change-Id: Ib460379f063eb83d393e1c5efe7333a643c1595e
Reviewed-on: https://go-review.googlesource.com/16942
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/src/runtime/os1_linux.go b/src/runtime/os1_linux.go
index 8b5cdd3465..5977b8437f 100644
--- a/src/runtime/os1_linux.go
+++ b/src/runtime/os1_linux.go
@@ -198,10 +198,7 @@ func mpreinit(mp *m) {
 }
 
 func msigsave(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
+	smask := &mp.sigmask
 	rtsigprocmask(_SIG_SETMASK, nil, smask, int32(unsafe.Sizeof(*smask)))
 }
 
@@ -218,7 +215,7 @@ func minit() {
 	_g_.m.procid = uint64(gettid())
 
 	// restore signal mask from m.sigmask and unblock essential signals
-	nmask := *(*sigset)(unsafe.Pointer(&_g_.m.sigmask))
+	nmask := _g_.m.sigmask
 	for i := range sigtable {
 		if sigtable[i].flags&_SigUnblock != 0 {
 			sigdelset(&nmask, i)
@@ -230,7 +227,7 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 func unminit() {
 	_g_ := getg()
-	smask := (*sigset)(unsafe.Pointer(&_g_.m.sigmask))
+	smask := &_g_.m.sigmask
 	rtsigprocmask(_SIG_SETMASK, smask, nil, int32(unsafe.Sizeof(*smask)))
 	signalstack(nil)
 }