runtime: preserve signal stack when calling Go on C thread

When calling a Go function on a C thread, if the C thread already has an
alternate signal stack, use that signal stack instead of installing a
new one.

Update #9896.

Change-Id: I62aa3a6a4a1dc4040fca050757299c8e6736987c
Reviewed-on: https://go-review.googlesource.com/18108
Reviewed-by: Russ Cox <rsc@golang.org>

misc/cgo/testcarchive/main4.c

@@ -0,0 +1,194 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Test a C thread that calls sigaltstack and then calls Go code.
+
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sched.h>
+#include <pthread.h>
+
+#include "libgo4.h"
+
+static void die(const char* msg) {
+	perror(msg);
+	exit(EXIT_FAILURE);
+}
+
+static int ok = 1;
+
+static void ioHandler(int signo, siginfo_t* info, void* ctxt) {
+}
+
+// Set up the SIGIO signal handler in a high priority constructor, so
+// that it is installed before the Go code starts.
+
+static void init(void) __attribute__ ((constructor (200)));
+
+static void init() {
+	struct sigaction sa;
+
+	memset(&sa, 0, sizeof sa);
+	sa.sa_sigaction = ioHandler;
+	if (sigemptyset(&sa.sa_mask) < 0) {
+		die("sigemptyset");
+	}
+	sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+	if (sigaction(SIGIO, &sa, NULL) < 0) {
+		die("sigaction");
+	}
+}
+
+// Test raising SIGIO on a C thread with an alternate signal stack
+// when there is a Go signal handler for SIGIO.
+static void* thread1(void* arg) {
+	pthread_t* ptid = (pthread_t*)(arg);
+	stack_t ss;
+	int i;
+	stack_t nss;
+
+	// Set up an alternate signal stack for this thread.
+	memset(&ss, 0, sizeof ss);
+	ss.ss_sp = malloc(SIGSTKSZ);
+	if (ss.ss_sp == NULL) {
+		die("malloc");
+	}
+	ss.ss_flags = 0;
+	ss.ss_size = SIGSTKSZ;
+	if (sigaltstack(&ss, NULL) < 0) {
+		die("sigaltstack");
+	}
+
+	// Send ourselves a SIGIO.  This will be caught by the Go
+	// signal handler which should forward to the C signal
+	// handler.
+	i = pthread_kill(*ptid, SIGIO);
+	if (i != 0) {
+		fprintf(stderr, "pthread_kill: %s\n", strerror(i));
+		exit(EXIT_FAILURE);
+	}
+
+	// Wait until the signal has been delivered.
+	i = 0;
+	while (SIGIOCount() == 0) {
+		if (sched_yield() < 0) {
+			perror("sched_yield");
+		}
+		i++;
+		if (i > 10000) {
+			fprintf(stderr, "looping too long waiting for signal\n");
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	// We should still be on the same signal stack.
+	if (sigaltstack(NULL, &nss) < 0) {
+		die("sigaltstack check");
+	}
+	if ((nss.ss_flags & SS_DISABLE) != 0) {
+		fprintf(stderr, "sigaltstack disabled on return from Go\n");
+		ok = 0;
+	} else if (nss.ss_sp != ss.ss_sp) {
+		fprintf(stderr, "sigalstack changed on return from Go\n");
+		ok = 0;
+	}
+
+	return NULL;
+}
+
+// Test calling a Go function to raise SIGIO on a C thread with an
+// alternate signal stack when there is a Go signal handler for SIGIO.
+static void* thread2(void* arg) {
+	pthread_t* ptid = (pthread_t*)(arg);
+	stack_t ss;
+	int i;
+	int oldcount;
+	stack_t nss;
+
+	// Set up an alternate signal stack for this thread.
+	memset(&ss, 0, sizeof ss);
+	ss.ss_sp = malloc(SIGSTKSZ);
+	if (ss.ss_sp == NULL) {
+		die("malloc");
+	}
+	ss.ss_flags = 0;
+	ss.ss_size = SIGSTKSZ;
+	if (sigaltstack(&ss, NULL) < 0) {
+		die("sigaltstack");
+	}
+
+	oldcount = SIGIOCount();
+
+	// Call a Go function that will call a C function to send us a
+	// SIGIO.
+	GoRaiseSIGIO(ptid);
+
+	// Wait until the signal has been delivered.
+	i = 0;
+	while (SIGIOCount() == oldcount) {
+		if (sched_yield() < 0) {
+			perror("sched_yield");
+		}
+		i++;
+		if (i > 10000) {
+			fprintf(stderr, "looping too long waiting for signal\n");
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	// We should still be on the same signal stack.
+	if (sigaltstack(NULL, &nss) < 0) {
+		die("sigaltstack check");
+	}
+	if ((nss.ss_flags & SS_DISABLE) != 0) {
+		fprintf(stderr, "sigaltstack disabled on return from Go\n");
+		ok = 0;
+	} else if (nss.ss_sp != ss.ss_sp) {
+		fprintf(stderr, "sigalstack changed on return from Go\n");
+		ok = 0;
+	}
+
+	return NULL;
+}
+
+int main(int argc, char **argv) {
+	pthread_t tid;
+	int i;
+
+	// Tell the Go library to start looking for SIGIO.
+	GoCatchSIGIO();
+
+	i = pthread_create(&tid, NULL, thread1, (void*)(&tid));
+	if (i != 0) {
+		fprintf(stderr, "pthread_create: %s\n", strerror(i));
+		exit(EXIT_FAILURE);
+	}
+
+	i = pthread_join(tid, NULL);
+	if (i != 0) {
+		fprintf(stderr, "pthread_join: %s\n", strerror(i));
+		exit(EXIT_FAILURE);
+	}
+
+	i = pthread_create(&tid, NULL, thread2, (void*)(&tid));
+	if (i != 0) {
+		fprintf(stderr, "pthread_create: %s\n", strerror(i));
+		exit(EXIT_FAILURE);
+	}
+
+	i = pthread_join(tid, NULL);
+	if (i != 0) {
+		fprintf(stderr, "pthread_join: %s\n", strerror(i));
+		exit(EXIT_FAILURE);
+	}
+
+	if (!ok) {
+		exit(EXIT_FAILURE);
+	}
+
+	printf("PASS\n");
+	return 0;
+}

misc/cgo/testcarchive/src/libgo4/libgo4.go

@@ -0,0 +1,52 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+/*
+#include <signal.h>
+#include <pthread.h>
+
+// Raise SIGIO.
+static void CRaiseSIGIO(pthread_t* p) {
+	pthread_kill(*p, SIGIO);
+}
+*/
+import "C"
+
+import (
+	"os"
+	"os/signal"
+	"sync/atomic"
+	"syscall"
+)
+
+var sigioCount int32
+
+// Catch SIGIO.
+//export GoCatchSIGIO
+func GoCatchSIGIO() {
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, syscall.SIGIO)
+	go func() {
+		for range c {
+			atomic.AddInt32(&sigioCount, 1)
+		}
+	}()
+}
+
+// Raise SIGIO.
+//export GoRaiseSIGIO
+func GoRaiseSIGIO(p *C.pthread_t) {
+	C.CRaiseSIGIO(p)
+}
+
+// Return the number of SIGIO signals seen.
+//export SIGIOCount
+func SIGIOCount() C.int {
+	return C.int(atomic.LoadInt32(&sigioCount))
+}
+
+func main() {
+}

misc/cgo/testcarchive/test.bash

@@ -77,4 +77,12 @@ if ! $bin; then
 fi
 rm -rf libgo3.a libgo3.h testp pkg
 
+GOPATH=$(pwd) go build -buildmode=c-archive -o libgo4.a libgo4
+$(go env CC) $(go env GOGCCFLAGS) $ccargs -o testp main4.c libgo4.a
+if ! $bin; then
+    echo "FAIL test4"
+    status=1
+fi
+rm -rf libgo4.a libgo4.h testp pkg
+
 exit $status

src/runtime/os1_darwin.go

@@ -152,7 +152,22 @@ func sigblock() {
 func minit() {
 	// Initialize signal handling.
 	_g_ := getg()
-	signalstack(&_g_.m.gsignal.stack)
+
+	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
+	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -167,7 +182,9 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 //go:nosplit
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 // Mach IPC, to get at semaphores

src/runtime/os1_dragonfly.go

@@ -141,7 +141,21 @@ func minit() {
 	_g_.m.procid = uint64(*(*int32)(unsafe.Pointer(&_g_.m.procid)))
 
 	// Initialize signal handling
-	signalstack(&_g_.m.gsignal.stack)
+	var st sigaltstackt
+	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
+	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -155,7 +169,9 @@ func minit() {
 
 // Called from dropm to undo the effect of an minit.
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 func memlimit() uintptr {

src/runtime/os1_freebsd.go

@@ -147,7 +147,21 @@ func minit() {
 	}
 
 	// Initialize signal handling.
-	signalstack(&_g_.m.gsignal.stack)
+	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
+	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -162,7 +176,9 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 //go:nosplit
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 func memlimit() uintptr {

src/runtime/os1_linux.go

@@ -221,7 +221,22 @@ func gettid() uint32
 func minit() {
 	// Initialize signal handling.
 	_g_ := getg()
-	signalstack(&_g_.m.gsignal.stack)
+
+	var st sigaltstackt
+	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
+	}
 
 	// for debuggers, in case cgo created the thread
 	_g_.m.procid = uint64(gettid())
@@ -239,7 +254,9 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 //go:nosplit
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 func memlimit() uintptr {

src/runtime/os1_netbsd.go

@@ -160,7 +160,21 @@ func minit() {
 	_g_.m.procid = uint64(lwp_self())
 
 	// Initialize signal handling
-	signalstack(&_g_.m.gsignal.stack)
+	var st sigaltstackt
+	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
+	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -175,7 +189,9 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 //go:nosplit
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 func memlimit() uintptr {

src/runtime/os1_openbsd.go

@@ -174,7 +174,21 @@ func minit() {
 	_g_.m.procid = uint64(*(*int32)(unsafe.Pointer(&_g_.m.procid)))
 
 	// Initialize signal handling
-	signalstack(&_g_.m.gsignal.stack)
+	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
+	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -189,7 +203,9 @@ func minit() {
 // Called from dropm to undo the effect of an minit.
 //go:nosplit
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 func memlimit() uintptr {

src/runtime/os3_solaris.go

@@ -213,7 +213,21 @@ func minit() {
 	_g_ := getg()
 	asmcgocall(unsafe.Pointer(funcPC(miniterrno)), unsafe.Pointer(&libc____errno))
 	// Initialize signal handling
-	signalstack(&_g_.m.gsignal.stack)
+	var st sigaltstackt
+	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 + uintptr(st.ss_size)
+		_g_.m.gsignal.stackguard0 = stsp + _StackGuard
+		_g_.m.gsignal.stackguard1 = stsp + _StackGuard
+		_g_.m.gsignal.stackAlloc = uintptr(st.ss_size)
+		_g_.m.newSigstack = false
+	}
 
 	// restore signal mask from m.sigmask and unblock essential signals
 	nmask := _g_.m.sigmask
@@ -227,7 +241,9 @@ func minit() {
 
 // Called from dropm to undo the effect of an minit.
 func unminit() {
-	signalstack(nil)
+	if getg().m.newSigstack {
+		signalstack(nil)
+	}
 }
 
 func memlimit() uintptr {

src/runtime/runtime2.go

@@ -303,6 +303,7 @@ type m struct {
 	spinning      bool // m is out of work and is actively looking for work
 	blocked       bool // m is blocked on a note
 	inwb          bool // m is executing a write barrier
+	newSigstack   bool // minit on C thread called sigaltstack
 	printlock     int8
 	fastrand      uint32
 	ncgocall      uint64 // number of cgo calls in total