[release-branch.go1.4] runtime: fix SIGPROF change

CL 2789 backported a change that required a barrage of followup CLs.
This CL backports all the followup CLs together.

There are manual edits to os_plan9.go and syscall_windows.go to take
the place of edits to defs_windows_{amd64,386}.go and os2_plan9.go
in the original. Those files do not exist in the release branch, but the
definition being added must go somewhere.

Original change descriptions below.

---

runtime/cgo: initialize our pthread_create wrapper earlier on openbsd

This is a genuine bug exposed by our test for issue 9456: our wrapper
for pthread_create is not initialized until we initialize cgo itself,
but it is possible that a static constructor could call pthread_create,
and in that case, it will be calling a nil function pointer.

Fix that by also initializing the sys_pthread_create function pointer
inside our pthread_create wrapper function, and use a pthread_once to
make sure it is only initialized once.

Fix build for openbsd.

Change-Id: Ica4da2c21fcaec186fdd3379128ef46f0e767ed7
Reviewed-on: https://go-review.googlesource.com/2232
Reviewed-by: David Crawshaw <crawshaw@golang.org>
(cherry picked from commit 77cd6197d7)

---

runtime: provide a dummy value of _SIGPROF on plan9 and windows

Fixes build on plan9 and windows.

Change-Id: Ic9b02c641ab84e4f6d8149de71b9eb495e3343b2
Reviewed-on: https://go-review.googlesource.com/2233
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
(cherry picked from commit 1f28238557)

---

runtime/cgo: remove unused variable

I missed this one in golang.org/cl/2232 and only tested the patch
on openbsd/amd64.

Change-Id: I4ff437ae0bfc61c989896c01904b6d33f9bdf0ec
Reviewed-on: https://go-review.googlesource.com/2234
Reviewed-by: Minux Ma <minux@golang.org>
(cherry picked from commit 0b2a74e89c)

---

runtime: skip TestCgoExternalThreadSIGPROF on OS X 10.6

The test program requires static constructor, which in turn needs
external linking to work, but external linking never works on 10.6.

This should fix the darwin-{386,amd64} builders.

Change-Id: I714fdd3e35f9a7e5f5659cf26367feec9412444f
Reviewed-on: https://go-review.googlesource.com/2235
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 2cbe27a272)

---

runtime: fix TestCgoExternalThreadSIGPROF again

Shell out to `uname -r` this time, so that the test will compile
even if the platform doesn't have syscall.Sysctl.

Change-Id: I3a19ab5d820bdb94586a97f4507b3837d7040525
Reviewed-on: https://go-review.googlesource.com/2271
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 865e5e98b6)

---

runtime: remove unnecessary GOOS switch

Change-Id: I8f518e273c02110042b08f7c50c3d38a648c8b6e
Reviewed-on: https://go-review.googlesource.com/2281
Reviewed-by: Minux Ma <minux@golang.org>
(cherry picked from commit 1ebfb082a7)

---

Change-Id: Ifee9667ca90eda2b074817c319b1b7c66d4f741d
Reviewed-on: https://go-review.googlesource.com/2805
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

src/runtime/cgo/gcc_openbsd_386.c

@@ -65,12 +65,39 @@ thread_start_wrapper(void *arg)
 	return args.func(args.arg);
 }
 
+static void init_pthread_wrapper(void) {
+	void *handle;
+
+	// Locate symbol for the system pthread_create function.
+	handle = dlopen("libpthread.so", RTLD_LAZY);
+	if(handle == NULL) {
+		fprintf(stderr, "runtime/cgo: dlopen failed to load libpthread: %s\n", dlerror());
+		abort();
+	}
+	sys_pthread_create = dlsym(handle, "pthread_create");
+	if(sys_pthread_create == NULL) {
+		fprintf(stderr, "runtime/cgo: dlsym failed to find pthread_create: %s\n", dlerror());
+		abort();
+	}
+	dlclose(handle);
+}
+
+static pthread_once_t init_pthread_wrapper_once = PTHREAD_ONCE_INIT;
+
 int
 pthread_create(pthread_t *thread, const pthread_attr_t *attr,
 	void *(*start_routine)(void *), void *arg)
 {
 	struct thread_args *p;
 
+	// we must initialize our wrapper in pthread_create, because it is valid to call
+	// pthread_create in a static constructor, and in fact, our test for issue 9456
+	// does just that.
+	if(pthread_once(&init_pthread_wrapper_once, init_pthread_wrapper) != 0) {
+		fprintf(stderr, "runtime/cgo: failed to initialize pthread_create wrapper\n");
+		abort();
+	}
+
 	p = malloc(sizeof(*p));
 	if(p == NULL) {
 		errno = ENOMEM;
@@ -87,7 +114,6 @@ x_cgo_init(G *g, void (*setg)(void*))
 {
 	pthread_attr_t attr;
 	size_t size;
-	void *handle;
 
 	setg_gcc = setg;
 	pthread_attr_init(&attr);
@@ -95,18 +121,10 @@ x_cgo_init(G *g, void (*setg)(void*))
 	g->stacklo = (uintptr)&attr - size + 4096;
 	pthread_attr_destroy(&attr);
 
-	// Locate symbol for the system pthread_create function.
-	handle = dlopen("libpthread.so", RTLD_LAZY);
-	if(handle == NULL) {
-		fprintf(stderr, "dlopen: failed to load libpthread: %s\n", dlerror());
+	if(pthread_once(&init_pthread_wrapper_once, init_pthread_wrapper) != 0) {
+		fprintf(stderr, "runtime/cgo: failed to initialize pthread_create wrapper\n");
 		abort();
 	}
-	sys_pthread_create = dlsym(handle, "pthread_create");
-	if(sys_pthread_create == NULL) {
-		fprintf(stderr, "dlsym: failed to find pthread_create: %s\n", dlerror());
-		abort();
-	}
-	dlclose(handle);
 
 	tcb_fixup(1);
 }

src/runtime/cgo/gcc_openbsd_amd64.c

@@ -65,12 +65,39 @@ thread_start_wrapper(void *arg)
 	return args.func(args.arg);
 }
 
+static void init_pthread_wrapper(void) {
+	void *handle;
+
+	// Locate symbol for the system pthread_create function.
+	handle = dlopen("libpthread.so", RTLD_LAZY);
+	if(handle == NULL) {
+		fprintf(stderr, "runtime/cgo: dlopen failed to load libpthread: %s\n", dlerror());
+		abort();
+	}
+	sys_pthread_create = dlsym(handle, "pthread_create");
+	if(sys_pthread_create == NULL) {
+		fprintf(stderr, "runtime/cgo: dlsym failed to find pthread_create: %s\n", dlerror());
+		abort();
+	}
+	dlclose(handle);
+}
+
+static pthread_once_t init_pthread_wrapper_once = PTHREAD_ONCE_INIT;
+
 int
 pthread_create(pthread_t *thread, const pthread_attr_t *attr,
 	void *(*start_routine)(void *), void *arg)
 {
 	struct thread_args *p;
 
+	// we must initialize our wrapper in pthread_create, because it is valid to call
+	// pthread_create in a static constructor, and in fact, our test for issue 9456
+	// does just that.
+	if(pthread_once(&init_pthread_wrapper_once, init_pthread_wrapper) != 0) {
+		fprintf(stderr, "runtime/cgo: failed to initialize pthread_create wrapper\n");
+		abort();
+	}
+
 	p = malloc(sizeof(*p));
 	if(p == NULL) {
 		errno = ENOMEM;
@@ -87,7 +114,6 @@ x_cgo_init(G *g, void (*setg)(void*))
 {
 	pthread_attr_t attr;
 	size_t size;
-	void *handle;
 
 	setg_gcc = setg;
 	pthread_attr_init(&attr);
@@ -95,18 +121,10 @@ x_cgo_init(G *g, void (*setg)(void*))
 	g->stacklo = (uintptr)&attr - size + 4096;
 	pthread_attr_destroy(&attr);
 
-	// Locate symbol for the system pthread_create function.
-	handle = dlopen("libpthread.so", RTLD_LAZY);
-	if(handle == NULL) {
-		fprintf(stderr, "dlopen: failed to load libpthread: %s\n", dlerror());
+	if(pthread_once(&init_pthread_wrapper_once, init_pthread_wrapper) != 0) {
+		fprintf(stderr, "runtime/cgo: failed to initialize pthread_create wrapper\n");
 		abort();
 	}
-	sys_pthread_create = dlsym(handle, "pthread_create");
-	if(sys_pthread_create == NULL) {
-		fprintf(stderr, "dlsym: failed to find pthread_create: %s\n", dlerror());
-		abort();
-	}
-	dlclose(handle);
 
 	tcb_fixup(1);
 }

src/runtime/crash_cgo_test.go

@@ -7,6 +7,7 @@
 package runtime_test
 
 import (
+	"os/exec"
 	"runtime"
 	"strings"
 	"testing"
@@ -52,8 +53,20 @@ func TestCgoExternalThreadPanic(t *testing.T) {
 
 func TestCgoExternalThreadSIGPROF(t *testing.T) {
 	// issue 9456.
-	if runtime.GOOS == "plan9" || runtime.GOOS == "windows" {
+	switch runtime.GOOS {
+	case "plan9", "windows":
 		t.Skipf("no pthreads on %s", runtime.GOOS)
+	case "darwin":
+		// static constructor needs external linking, but we don't support
+		// external linking on OS X 10.6.
+		out, err := exec.Command("uname", "-r").Output()
+		if err != nil {
+			t.Fatalf("uname -r failed: %v", err)
+		}
+		// OS X 10.6 == Darwin 10.x
+		if strings.HasPrefix(string(out), "10.") {
+			t.Skipf("no external linking on OS X 10.6")
+		}
 	}
 	got := executeTest(t, cgoExternalThreadSIGPROFSource, nil)
 	want := "OK\n"

src/runtime/defs_windows.go

@@ -41,6 +41,7 @@ const (
 	DUPLICATE_SAME_ACCESS   = C.DUPLICATE_SAME_ACCESS
 	THREAD_PRIORITY_HIGHEST = C.THREAD_PRIORITY_HIGHEST
 
+	SIGPROF          = 0 // dummy value for badsignal
 	SIGINT           = C.SIGINT
 	CTRL_C_EVENT     = C.CTRL_C_EVENT
 	CTRL_BREAK_EVENT = C.CTRL_BREAK_EVENT

src/runtime/os_plan9.go

@@ -6,6 +6,8 @@ package runtime
 
 import "unsafe"
 
+const _SIGPROF = 0 // dummy value for badsignal
+
 func pread(fd int32, buf unsafe.Pointer, nbytes int32, offset int64) int32
 func pwrite(fd int32, buf unsafe.Pointer, nbytes int32, offset int64) int32
 func seek(fd int32, offset int64, whence int32) int64

src/runtime/sigqueue.go

@@ -160,7 +160,7 @@ func badsignal(sig uintptr) {
 	// call to cgocallback below will bring down the whole process.
 	// It's better to miss a few SIGPROF signals than to abort in this case.
 	// See http://golang.org/issue/9456.
-	if sig == _SIGPROF && needextram != 0 {
+	if _SIGPROF != 0 && sig == _SIGPROF && needextram != 0 {
 		return
 	}
 	cgocallback(unsafe.Pointer(funcPC(sigsend)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig))

src/runtime/syscall_windows.go

@@ -8,6 +8,8 @@ import (
 	"unsafe"
 )
 
+const _SIGPROF = 0 // dummy value for badsignal
+
 type callbacks struct {
 	lock mutex
 	ctxt [cb_max]*wincallbackcontext