runtime: for c-archive/c-shared, install signal handlers synchronously

The previous behaviour of installing the signal handlers in a separate thread meant that Go initialization raced with non-Go initialization if the non-Go initialization also wanted to install signal handlers. Make installing signal handlers synchronous so that the process-wide behavior is predictable. Update #9896. Change-Id: Ice24299877ec46f8518b072a381932d273096a32 Reviewed-on: https://go-review.googlesource.com/18150 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Crawshaw <crawshaw@golang.org>
golang · Jan 9, 2016 · 21b4f23 · 21b4f23
1 parent 0b3807a
commit 21b4f23
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Showing 23 changed files with 200 additions and 12 deletions.
diff --git a/misc/cgo/testcarchive/main.c b/misc/cgo/testcarchive/main.c
@@ -2,15 +2,44 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+#include <signal.h>
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "p.h"
 #include "libgo.h"
 
+static void (*oldHandler)(int, siginfo_t*, void*);
+
+static void handler(int signo, siginfo_t* info, void* ctxt) {
+	if (oldHandler) {
+		oldHandler(signo, info, ctxt);
+	}
+}
+
 int main(void) {
+	struct sigaction sa;
+	struct sigaction osa;
 	int32_t res;
 
+	// Install our own signal handler.
+	memset(&sa, 0, sizeof sa);
+	sa.sa_sigaction = handler;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
+	memset(&osa, 0, sizeof osa);
+	sigemptyset(&osa.sa_mask);
+	if (sigaction(SIGSEGV, &sa, &osa) < 0) {
+		perror("sigaction");
+		return 2;
+	}
+	if (osa.sa_handler == SIG_DFL || (osa.sa_flags&SA_ONSTACK) == 0) {
+		fprintf(stderr, "Go runtime did not install signal handler\n");
+		return 2;
+	}
+	oldHandler = osa.sa_sigaction;
+
 	if (!DidInitRun()) {
 		fprintf(stderr, "ERROR: buildmode=c-archive init should run\n");
 		return 2;
@@ -21,6 +50,16 @@ int main(void) {
 		return 2;
 	}
 
+	// Make sure our signal handler is still the one in use.
+	if (sigaction(SIGSEGV, NULL, &sa) < 0) {
+		perror("sigaction check");
+		return 2;
+	}
+	if (sa.sa_sigaction != handler) {
+		fprintf(stderr, "ERROR: wrong signal handler: %p != %p\n", sa.sa_sigaction, handler);
+		return 2;
+	}
+
 	res = FromPkg();
 	if (res != 1024) {
 		fprintf(stderr, "ERROR: FromPkg()=%d, want 1024\n", res);

diff --git a/src/os/signal/doc.go b/src/os/signal/doc.go
@@ -172,7 +172,10 @@ When Go code is built with options like -buildmode=c-shared, it will
 be run as part of an existing non-Go program. The non-Go code may
 have already installed signal handlers when the Go code starts (that
 may also happen in unusual cases when using cgo or SWIG; in that case,
-the discussion here applies).
+the discussion here applies).  For -buildmode=c-archive the Go runtime
+will initialize signals at global constructor time.  For
+-buildmode=c-shared the Go runtime will initialize signals when the
+shared library is loaded.
 
 If the Go runtime sees an existing signal handler for the SIGCANCEL or
 SIGSETXID signals (which are used only on GNU/Linux), it will turn on

diff --git a/src/runtime/os1_darwin.go b/src/runtime/os1_darwin.go
@@ -125,6 +125,15 @@ func newosproc0(stacksize uintptr, fn unsafe.Pointer, fnarg uintptr) {
 var failallocatestack = []byte("runtime: failed to allocate stack for the new OS thread\n")
 var failthreadcreate = []byte("runtime: failed to create new OS thread\n")
 
+// Called to do synchronous initialization of Go code built with
+// -buildmode=c-archive or -buildmode=c-shared.
+// None of the Go runtime is initialized.
+//go:nosplit
+//go:nowritebarrierrec
+func libpreinit() {
+	initsig(true)
+}
+
 // 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) {
@@ -459,6 +468,8 @@ func memlimit() uintptr {
 	return 0
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK
@@ -471,6 +482,8 @@ func setsig(i int32, fn uintptr, restart bool) {
 	sigaction(uint32(i), &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	var osa usigactiont
 	sigaction(uint32(i), nil, &osa)
@@ -486,6 +499,8 @@ func setsigstack(i int32) {
 	sigaction(uint32(i), &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa usigactiont
 	sigaction(uint32(i), nil, &sa)
@@ -505,6 +520,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m sigmask) {
 	s := sigset(m[0])
 	sigprocmask(_SIG_SETMASK, &s, nil)

diff --git a/src/runtime/os1_dragonfly.go b/src/runtime/os1_dragonfly.go
@@ -213,6 +213,8 @@ type sigactiont struct {
 	sa_mask      sigset
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK
@@ -227,10 +229,14 @@ func setsig(i int32, fn uintptr, restart bool) {
 	sigaction(i, &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	throw("setsigstack")
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa sigactiont
 	sigaction(i, nil, &sa)
@@ -253,6 +259,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m sigmask) {
 	var mask sigset
 	copy(mask.__bits[:], m[:])

diff --git a/src/runtime/os1_freebsd.go b/src/runtime/os1_freebsd.go
@@ -220,6 +220,8 @@ type sigactiont struct {
 	sa_mask    sigset
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK
@@ -234,10 +236,14 @@ func setsig(i int32, fn uintptr, restart bool) {
 	sigaction(i, &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	throw("setsigstack")
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa sigactiont
 	sigaction(i, nil, &sa)
@@ -260,6 +266,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m [(_NSIG + 31) / 32]uint32) {
 	var mask sigset
 	copy(mask.__bits[:], m[:])

diff --git a/src/runtime/os1_linux.go b/src/runtime/os1_linux.go
@@ -190,6 +190,15 @@ func goenvs() {
 	goenvs_unix()
 }
 
+// Called to do synchronous initialization of Go code built with
+// -buildmode=c-archive or -buildmode=c-shared.
+// None of the Go runtime is initialized.
+//go:nosplit
+//go:nowritebarrierrec
+func libpreinit() {
+	initsig(true)
+}
+
 // 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) {
@@ -298,6 +307,8 @@ func memlimit() uintptr {
 func sigreturn()
 func sigtramp()
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 	memclr(unsafe.Pointer(&sa), unsafe.Sizeof(sa))
@@ -316,12 +327,11 @@ func setsig(i int32, fn uintptr, restart bool) {
 		fn = funcPC(sigtramp)
 	}
 	sa.sa_handler = fn
-	// Qemu rejects rt_sigaction of SIGRTMAX (64).
-	if rt_sigaction(uintptr(i), &sa, nil, unsafe.Sizeof(sa.sa_mask)) != 0 && i != 64 {
-		throw("rt_sigaction failure")
-	}
+	rt_sigaction(uintptr(i), &sa, nil, unsafe.Sizeof(sa.sa_mask))
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	var sa sigactiont
 	if rt_sigaction(uintptr(i), nil, &sa, unsafe.Sizeof(sa.sa_mask)) != 0 {
@@ -336,6 +346,8 @@ func setsigstack(i int32) {
 	}
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa sigactiont
 
@@ -362,6 +374,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m sigmask) {
 	var mask sigset
 	sigcopyset(&mask, m)

diff --git a/src/runtime/os1_nacl.go b/src/runtime/os1_nacl.go
@@ -67,7 +67,7 @@ func goenvs() {
 	goenvs_unix()
 }
 
-func initsig() {
+func initsig(preinit bool) {
 }
 
 //go:nosplit

diff --git a/src/runtime/os1_netbsd.go b/src/runtime/os1_netbsd.go
@@ -206,6 +206,8 @@ type sigactiont struct {
 	sa_flags     int32
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK
@@ -220,10 +222,14 @@ func setsig(i int32, fn uintptr, restart bool) {
 	sigaction(i, &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	throw("setsigstack")
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa sigactiont
 	sigaction(i, nil, &sa)
@@ -246,6 +252,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m sigmask) {
 	var mask sigset
 	copy(mask.__bits[:], m[:])

diff --git a/src/runtime/os1_openbsd.go b/src/runtime/os1_openbsd.go
@@ -220,6 +220,8 @@ type sigactiont struct {
 	sa_flags     int32
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 	sa.sa_flags = _SA_SIGINFO | _SA_ONSTACK
@@ -234,10 +236,14 @@ func setsig(i int32, fn uintptr, restart bool) {
 	sigaction(i, &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	throw("setsigstack")
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa sigactiont
 	sigaction(i, nil, &sa)
@@ -260,6 +266,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m sigmask) {
 	sigprocmask(_SIG_SETMASK, sigset(m[0]))
 }

diff --git a/src/runtime/os1_plan9.go b/src/runtime/os1_plan9.go
@@ -107,7 +107,7 @@ func getRandomData(r []byte) {
 func goenvs() {
 }
 
-func initsig() {
+func initsig(preinit bool) {
 }
 
 //go:nosplit

diff --git a/src/runtime/os3_solaris.go b/src/runtime/os3_solaris.go
@@ -279,6 +279,8 @@ func memlimit() uintptr {
 
 func sigtramp()
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsig(i int32, fn uintptr, restart bool) {
 	var sa sigactiont
 
@@ -295,6 +297,8 @@ func setsig(i int32, fn uintptr, restart bool) {
 	sigaction(i, &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func setsigstack(i int32) {
 	var sa sigactiont
 	sigaction(i, nil, &sa)
@@ -306,6 +310,8 @@ func setsigstack(i int32) {
 	sigaction(i, &sa, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func getsig(i int32) uintptr {
 	var sa sigactiont
 	sigaction(i, nil, &sa)
@@ -328,6 +334,8 @@ func signalstack(s *stack) {
 	sigaltstack(&st, nil)
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func updatesigmask(m sigmask) {
 	var mask sigset
 	copy(mask.__sigbits[:], m[:])
@@ -478,6 +486,8 @@ func pthread_create(thread *pthread, attr *pthreadattr, fn uintptr, arg unsafe.P
 	return int32(sysvicall4(&libc_pthread_create, uintptr(unsafe.Pointer(thread)), uintptr(unsafe.Pointer(attr)), uintptr(fn), uintptr(arg)))
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func raise(sig int32) /* int32 */ {
 	sysvicall1(&libc_raise, uintptr(sig))
 }
@@ -516,6 +526,8 @@ func setitimer(which int32, value *itimerval, ovalue *itimerval) /* int32 */ {
 	sysvicall3(&libc_setitimer, uintptr(which), uintptr(unsafe.Pointer(value)), uintptr(unsafe.Pointer(ovalue)))
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func sigaction(sig int32, act *sigactiont, oact *sigactiont) /* int32 */ {
 	sysvicall3(&libc_sigaction, uintptr(sig), uintptr(unsafe.Pointer(act)), uintptr(unsafe.Pointer(oact)))
 }
@@ -527,6 +539,7 @@ func sigaltstack(ss *sigaltstackt, oss *sigaltstackt) /* int32 */ {
 }
 
 //go:nosplit
+//go:nowritebarrierrec
 func sigprocmask(how int32, set *sigset, oset *sigset) /* int32 */ {
 	sysvicall3(&libc_sigprocmask, uintptr(how), uintptr(unsafe.Pointer(set)), uintptr(unsafe.Pointer(oset)))
 }