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.

[Replay of CL 16942 by Elias Naur.]

Change-Id: I98f144d626033ae5318576115ed635415ac71b2c
Reviewed-on: https://go-review.googlesource.com/17033Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>

src/runtime/os1_darwin.go

@@ -8,7 +8,9 @@ import "unsafe"
 
 //extern SigTabTT runtime·sigtab[];
 
-var sigset_all = ^uint32(0)
+type sigset uint32
+
+var sigset_all = ^sigset(0)
 
 func unimplemented(name string) {
 	println(name, "not implemented")
@@ -83,7 +85,7 @@ func newosproc(mp *m, stk unsafe.Pointer) {
 		print("newosproc stk=", stk, " m=", mp, " g=", mp.g0, " id=", mp.id, " ostk=", &mp, "\n")
 	}
 
-	var oset uint32
+	var oset sigset
 	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
 	errno := bsdthread_create(stk, unsafe.Pointer(mp), funcPC(mstart))
 	sigprocmask(_SIG_SETMASK, &oset, nil)
@@ -109,7 +111,7 @@ func newosproc0(stacksize uintptr, fn unsafe.Pointer, fnarg uintptr) {
 	}
 	stk := unsafe.Pointer(uintptr(stack) + stacksize)
 
-	var oset uint32
+	var oset sigset
 	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
 	errno := bsdthread_create(stk, fn, fnarg)
 	sigprocmask(_SIG_SETMASK, &oset, nil)
@@ -132,17 +134,12 @@ func mpreinit(mp *m) {
 
 //go:nosplit
 func msigsave(mp *m) {
-	smask := (*uint32)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
-	sigprocmask(_SIG_SETMASK, nil, smask)
+	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := (*uint32)(unsafe.Pointer(&mp.sigmask))
-	sigprocmask(_SIG_SETMASK, smask, nil)
+	sigprocmask(_SIG_SETMASK, &mp.sigmask, nil)
 }
 
 //go:nosplit
@@ -158,7 +155,7 @@ func minit() {
 	signalstack(&_g_.m.gsignal.stack)
 
 	// restore signal mask from m.sigmask and unblock essential signals
-	nmask := *(*uint32)(unsafe.Pointer(&_g_.m.sigmask))
+	nmask := _g_.m.sigmask
 	for i := range sigtable {
 		if sigtable[i].flags&_SigUnblock != 0 {
 			nmask &^= 1 << (uint32(i) - 1)
@@ -483,10 +480,11 @@ func signalstack(s *stack) {
 }
 
 func updatesigmask(m sigmask) {
-	sigprocmask(_SIG_SETMASK, &m[0], nil)
+	s := sigset(m[0])
+	sigprocmask(_SIG_SETMASK, &s, nil)
 }
 
 func unblocksig(sig int32) {
-	mask := uint32(1) << (uint32(sig) - 1)
+	mask := sigset(1) << (uint32(sig) - 1)
 	sigprocmask(_SIG_UNBLOCK, &mask, nil)
 }

src/runtime/os1_dragonfly.go

@@ -119,17 +119,12 @@ func mpreinit(mp *m) {
 
 //go:nosplit
 func msigsave(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
-	sigprocmask(_SIG_SETMASK, nil, smask)
+	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	sigprocmask(_SIG_SETMASK, smask, nil)
+	sigprocmask(_SIG_SETMASK, &mp.sigmask, nil)
 }
 
 //go:nosplit
@@ -149,7 +144,7 @@ func minit() {
 	signalstack(&_g_.m.gsignal.stack)
 
 	// 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 {
 			nmask.__bits[(i-1)/32] &^= 1 << ((uint32(i) - 1) & 31)

src/runtime/os1_freebsd.go

@@ -122,17 +122,12 @@ func mpreinit(mp *m) {
 
 //go:nosplit
 func msigsave(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
-	sigprocmask(_SIG_SETMASK, nil, smask)
+	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	sigprocmask(_SIG_SETMASK, smask, nil)
+	sigprocmask(_SIG_SETMASK, &mp.sigmask, nil)
 }
 
 //go:nosplit
@@ -155,7 +150,7 @@ func minit() {
 	signalstack(&_g_.m.gsignal.stack)
 
 	// 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 {
 			nmask.__bits[(i-1)/32] &^= 1 << ((uint32(i) - 1) & 31)

src/runtime/os1_linux.go

@@ -199,16 +199,13 @@ func mpreinit(mp *m) {
 
 //go:nosplit
 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)))
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
+	smask := &mp.sigmask
 	rtsigprocmask(_SIG_SETMASK, smask, nil, int32(unsafe.Sizeof(*smask)))
 }
 
@@ -230,7 +227,7 @@ 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)

src/runtime/os1_nacl.go

@@ -6,6 +6,8 @@ package runtime
 
 import "unsafe"
 
+type sigset struct{}
+
 // Called to initialize a new m (including the bootstrap m).
 // Called on the parent thread (main thread in case of bootstrap), can allocate memory.
 func mpreinit(mp *m) {

src/runtime/os1_netbsd.go

@@ -140,17 +140,12 @@ func mpreinit(mp *m) {
 
 //go:nosplit
 func msigsave(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
-	sigprocmask(_SIG_SETMASK, nil, smask)
+	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	sigprocmask(_SIG_SETMASK, smask, nil)
+	sigprocmask(_SIG_SETMASK, &mp.sigmask, nil)
 }
 
 //go:nosplit
@@ -168,7 +163,7 @@ func minit() {
 	signalstack(&_g_.m.gsignal.stack)
 
 	// 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 {
 			nmask.__bits[(i-1)/32] &^= 1 << ((uint32(i) - 1) & 31)

src/runtime/os1_openbsd.go

@@ -22,9 +22,11 @@ const (
 	_CLOCK_MONOTONIC = 3
 )
 
+type sigset uint32
+
 const (
-	sigset_none = uint32(0)
-	sigset_all  = ^uint32(0)
+	sigset_none = sigset(0)
+	sigset_all  = ^sigset(0)
 )
 
 // From OpenBSD's <sys/sysctl.h>
@@ -150,17 +152,12 @@ func mpreinit(mp *m) {
 
 //go:nosplit
 func msigsave(mp *m) {
-	smask := (*uint32)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
-	*smask = sigprocmask(_SIG_BLOCK, 0)
+	mp.sigmask = sigprocmask(_SIG_BLOCK, 0)
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := *(*uint32)(unsafe.Pointer(&mp.sigmask))
-	sigprocmask(_SIG_SETMASK, smask)
+	sigprocmask(_SIG_SETMASK, mp.sigmask)
 }
 
 //go:nosplit
@@ -180,7 +177,7 @@ func minit() {
 	signalstack(&_g_.m.gsignal.stack)
 
 	// restore signal mask from m.sigmask and unblock essential signals
-	nmask := *(*uint32)(unsafe.Pointer(&_g_.m.sigmask))
+	nmask := _g_.m.sigmask
 	for i := range sigtable {
 		if sigtable[i].flags&_SigUnblock != 0 {
 			nmask &^= 1 << (uint32(i) - 1)
@@ -213,7 +210,7 @@ func setsig(i int32, fn uintptr, restart bool) {
 	if restart {
 		sa.sa_flags |= _SA_RESTART
 	}
-	sa.sa_mask = sigset_all
+	sa.sa_mask = uint32(sigset_all)
 	if fn == funcPC(sighandler) {
 		fn = funcPC(sigtramp)
 	}
@@ -248,10 +245,10 @@ func signalstack(s *stack) {
 }
 
 func updatesigmask(m sigmask) {
-	sigprocmask(_SIG_SETMASK, m[0])
+	sigprocmask(_SIG_SETMASK, sigset(m[0]))
 }
 
 func unblocksig(sig int32) {
-	mask := uint32(1) << (uint32(sig) - 1)
+	mask := sigset(1) << (uint32(sig) - 1)
 	sigprocmask(_SIG_UNBLOCK, mask)
 }

src/runtime/os1_plan9.go

@@ -9,6 +9,8 @@ import (
 	"unsafe"
 )
 
+type sigset struct{}
+
 // Called to initialize a new m (including the bootstrap m).
 // Called on the parent thread (main thread in case of bootstrap), can allocate memory.
 func mpreinit(mp *m) {

src/runtime/os1_windows.go

@@ -97,6 +97,8 @@ var (
 	_GetQueuedCompletionStatusEx stdFunction
 )
 
+type sigset struct{}
+
 // Call a Windows function with stdcall conventions,
 // and switch to os stack during the call.
 func asmstdcall(fn unsafe.Pointer)

src/runtime/os3_solaris.go

@@ -194,17 +194,12 @@ func miniterrno()
 
 //go:nosplit
 func msigsave(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	if unsafe.Sizeof(*smask) > unsafe.Sizeof(mp.sigmask) {
-		throw("insufficient storage for signal mask")
-	}
-	sigprocmask(_SIG_SETMASK, nil, smask)
+	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
 }
 
 //go:nosplit
 func msigrestore(mp *m) {
-	smask := (*sigset)(unsafe.Pointer(&mp.sigmask))
-	sigprocmask(_SIG_SETMASK, smask, nil)
+	sigprocmask(_SIG_SETMASK, &mp.sigmask, nil)
 }
 
 //go:nosplit
@@ -221,7 +216,7 @@ func minit() {
 	signalstack(&_g_.m.gsignal.stack)
 
 	// 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 {
 			nmask.__sigbits[(i-1)/32] &^= 1 << ((uint32(i) - 1) & 31)

src/runtime/os_darwin.go

@@ -24,7 +24,7 @@ func mach_thread_self() uint32
 func sysctl(mib *uint32, miblen uint32, out *byte, size *uintptr, dst *byte, ndst uintptr) int32
 
 //go:noescape
-func sigprocmask(how uint32, new, old *uint32)
+func sigprocmask(how uint32, new, old *sigset)
 
 //go:noescape
 func sigaction(mode uint32, new, old *sigactiont)

src/runtime/os_openbsd.go

@@ -18,7 +18,7 @@ func sigaction(sig int32, new, old *sigactiont)
 func sigaltstack(new, old *stackt)
 
 //go:noescape
-func sigprocmask(mode int32, new uint32) uint32
+func sigprocmask(mode int32, new sigset) sigset
 
 //go:noescape
 func sysctl(mib *uint32, miblen uint32, out *byte, size *uintptr, dst *byte, ndst uintptr) int32

src/runtime/runtime2.go

@@ -284,7 +284,7 @@ type m struct {
 	// Fields not known to debuggers.
 	procid        uint64     // for debuggers, but offset not hard-coded
 	gsignal       *g         // signal-handling g
-	sigmask       [4]uintptr // storage for saved signal mask
+	sigmask       sigset     // storage for saved signal mask
 	tls           [6]uintptr // thread-local storage (for x86 extern register)
 	mstartfn      func()
 	curg          *g       // current running goroutine