runtime: scheduler, cgo reorganization

* Change use of m->g0 stack (aka scheduler stack).
* Provide runtime.mcall(f) to invoke f() on m->g0 stack.
* Replace scheduler loop entry with runtime.mcall(schedule).

Runtime.mcall eliminates the need for fake scheduler states that
exist just to run a bit of code on the m->g0 stack
(Grecovery, Gstackalloc).

The elimination of the scheduler as a loop that stops and
starts using gosave and gogo fixes a bad interaction with the
way cgo uses the m->g0 stack.  Cgo runs external (gcc-compiled)
C functions on that stack, and then when calling back into Go,
it sets m->g0->sched.sp below the added call frames, so that
other uses of m->g0's stack will not interfere with those frames.
Unfortunately, gogo (longjmp) back to the scheduler loop at
this point would end up running scheduler with the lower
sp, which no longer points at a valid stack frame for
a call to scheduler.  If scheduler then wrote any function call
arguments or local variables to where it expected the stack
frame to be, it would overwrite other data on the stack.
I realized this possibility while debugging a problem with
calling complex Go code in a Go -> C -> Go cgo callback.
This wasn't the bug I was looking for, it turns out, but I believe
it is a real bug nonetheless.  Switching to runtime.mcall, which
only adds new frames to the stack and never jumps into
functions running in existing ones, fixes this bug.

* Move cgo-related code out of proc.c into cgocall.c.
* Add very large comment describing cgo call sequences.
* Simpilify, regularize cgo function implementations and names.
* Add test suite as misc/cgo/test.

Now the Go -> C path calls cgocall, which calls asmcgocall,
and the C -> Go path calls cgocallback, which calls cgocallbackg.

The shuffling, which affects mainly the callback case, moves
most of the callback implementation to cgocallback running
on the m->curg stack (not the m->g0 scheduler stack) and
only while accounted for with $GOMAXPROCS (between calls
to exitsyscall and entersyscall).

The previous callback code did not block in startcgocallback's
approximation to exitsyscall, so if, say, the garbage collector
were running, it would still barge in and start doing things
like call malloc.  Similarly endcgocallback's approximation of
entersyscall did not call matchmg to kick off new OS threads
when necessary, which caused the bug in issue 1560.

Fixes #1560.

R=iant
CC=golang-dev
https://golang.org/cl/4253054

Author: rsc

misc/cgo/stdio/Makefile

@@ -6,10 +6,7 @@ include ../../../src/Make.inc
 
 TARG=stdio
 CGOFILES=\
-	align.go\
 	file.go\
-	test.go\
-	test1.go\
 
 CLEANFILES+=hello fib chain run.out
 

misc/cgo/stdio/hello.go

@@ -4,26 +4,8 @@
 
 package main
 
-import (
-	"os"
-	"stdio"
-)
+import "stdio"
 
 func main() {
 	stdio.Stdout.WriteString(stdio.Greeting + "\n")
-
-	l := stdio.Atol("123")
-	if l != 123 {
-		println("Atol 123: ", l)
-		panic("bad atol")
-	}
-
-	n, err := stdio.Strtol("asdf", 123)
-	if n != 0 || err != os.EINVAL {
-		println("Strtol: ", n, err)
-		panic("bad atoi2")
-	}
-
-	stdio.TestAlign()
-	stdio.TestEnum()
 }

misc/cgo/test/Makefile

@@ -0,0 +1,23 @@
+# Copyright 2011 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.
+
+include ../../../src/Make.inc
+
+TARG=runtime/cgotest
+
+CGOFILES=\
+	align.go\
+	basic.go\
+	callback.go\
+	issue1222.go\
+	issue1328.go\
+	issue1560.go\
+
+CGO_OFILES=\
+	callback_c.o\
+
+OFILES=\
+	runtime.$O\
+
+include ../../../src/Make.pkg

misc/cgo/stdio/align.go renamed to misc/cgo/test/align.go

@@ -1,4 +1,4 @@
-package stdio
+package cgotest
 
 /*
 #include <stdio.h>
@@ -55,24 +55,18 @@ void cTest(SDL_KeyboardEvent *event) {
 import "C"
 
 import (
-	"fmt"
-	"syscall"
+	"testing"
 )
 
-func TestAlign() {
-	if syscall.ARCH == "amd64" {
-		// alignment is known to be broken on amd64.
-		// http://code.google.com/p/go/issues/detail?id=609
-		return
-	}
+func TestAlign(t *testing.T) {
 	var evt C.SDL_KeyboardEvent
 	C.makeEvent(&evt)
 	if C.same(&evt, evt.typ, evt.which, evt.state, evt.keysym.scancode, evt.keysym.sym, evt.keysym.mod, evt.keysym.unicode) == 0 {
-		fmt.Println("*** bad alignment")
+		t.Error("*** bad alignment")
 		C.cTest(&evt)
-		fmt.Printf("Go: %#x %#x %#x %#x %#x %#x %#x\n",
+		t.Errorf("Go: %#x %#x %#x %#x %#x %#x %#x\n",
 			evt.typ, evt.which, evt.state, evt.keysym.scancode,
 			evt.keysym.sym, evt.keysym.mod, evt.keysym.unicode)
-		fmt.Println(evt)
+		t.Error(evt)
 	}
 }

misc/cgo/stdio/test.go renamed to misc/cgo/test/basic.go

@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// This file contains test cases for cgo.
+// Basic test cases for cgo.
 
-package stdio
+package cgotest
 
 /*
 #include <stdio.h>
@@ -52,6 +52,7 @@ struct ibv_context {
 import "C"
 import (
 	"os"
+	"testing"
 	"unsafe"
 )
 
@@ -89,38 +90,35 @@ func Atol(s string) int {
 	return int(n)
 }
 
-func TestConst() {
+func TestConst(t *testing.T) {
 	C.myConstFunc(nil, 0, nil)
 }
 
-func TestEnum() {
+func TestEnum(t *testing.T) {
 	if C.Enum1 != 1 || C.Enum2 != 2 {
-		println("bad enum", C.Enum1, C.Enum2)
+		t.Error("bad enum", C.Enum1, C.Enum2)
 	}
 }
 
-func TestAtol() {
+func TestAtol(t *testing.T) {
 	l := Atol("123")
 	if l != 123 {
-		println("Atol 123: ", l)
-		panic("bad atol")
+		t.Error("Atol 123: ", l)
 	}
 }
 
-func TestErrno() {
+func TestErrno(t *testing.T) {
 	n, err := Strtol("asdf", 123)
 	if n != 0 || err != os.EINVAL {
-		println("Strtol: ", n, err)
-		panic("bad strtol")
+		t.Error("Strtol: ", n, err)
 	}
 }
 
-func TestMultipleAssign() {
-	p := C.CString("123")
+func TestMultipleAssign(t *testing.T) {
+	p := C.CString("234")
 	n, m := C.strtol(p, nil, 345), C.strtol(p, nil, 10)
 	if n != 0 || m != 234 {
-		println("Strtol x2: ", n, m)
-		panic("bad strtol x2")
+		t.Fatal("Strtol x2: ", n, m)
 	}
 	C.free(unsafe.Pointer(p))
 }
@@ -134,11 +132,3 @@ var (
 type Context struct {
 	ctx *C.struct_ibv_context
 }
-
-func Test() {
-	TestAlign()
-	TestAtol()
-	TestEnum()
-	TestErrno()
-	TestConst()
-}

misc/cgo/test/callback.go

@@ -0,0 +1,136 @@
+package cgotest
+
+/*
+void callback(void *f);
+void callGoFoo(void) {
+	extern void goFoo(void);
+	goFoo();
+}
+*/
+import "C"
+
+import (
+	"runtime"
+	"testing"
+	"unsafe"
+)
+
+// nestedCall calls into C, back into Go, and finally to f.
+func nestedCall(f func()) {
+	// NOTE: Depends on representation of f.
+	// callback(x) calls goCallback(x)
+	C.callback(*(*unsafe.Pointer)(unsafe.Pointer(&f)))
+}
+
+//export goCallback
+func goCallback(p unsafe.Pointer) {
+	(*(*func())(unsafe.Pointer(&p)))()
+}
+
+func TestCallback(t *testing.T) {
+	var x = false
+	nestedCall(func(){x = true})
+	if !x {
+		t.Fatal("nestedCall did not call func")
+	}
+}
+
+func TestCallbackGC(t *testing.T) {
+	nestedCall(runtime.GC)
+}
+
+func lockedOSThread() bool  // in runtime.c
+
+func TestCallbackPanic(t *testing.T) {
+	// Make sure panic during callback unwinds properly.
+	if lockedOSThread() {
+		t.Fatal("locked OS thread on entry to TestCallbackPanic")
+	}
+	defer func() {
+		s := recover()
+		if s == nil {
+			t.Fatal("did not panic")
+		}
+		if s.(string) != "callback panic" {
+			t.Fatal("wrong panic:", s)
+		}
+		if lockedOSThread() {
+			t.Fatal("locked OS thread on exit from TestCallbackPanic")
+		}
+	}()
+	nestedCall(func(){panic("callback panic")})
+	panic("nestedCall returned")
+}
+
+func TestCallbackPanicLoop(t *testing.T) {
+	// Make sure we don't blow out m->g0 stack.
+	for i := 0; i < 100000; i++ {
+		TestCallbackPanic(t)
+	}
+}
+
+func TestCallbackPanicLocked(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	if !lockedOSThread() {
+		t.Fatal("runtime.LockOSThread didn't")
+	}
+	defer func() {
+		s := recover()
+		if s == nil {
+			t.Fatal("did not panic")
+		}
+		if s.(string) != "callback panic" {
+			t.Fatal("wrong panic:", s)
+		}
+		if !lockedOSThread() {
+			t.Fatal("lost lock on OS thread after panic")
+		}
+	}()
+	nestedCall(func(){panic("callback panic")})
+	panic("nestedCall returned")
+}
+
+// Callback with zero arguments used to make the stack misaligned,
+// which broke the garbage collector and other things.
+func TestZeroArgCallback(t *testing.T) {
+	defer func() {
+		s := recover()
+		if s != nil {
+			t.Fatal("panic during callback:", s)
+		}
+	}()
+	C.callGoFoo()
+}
+
+//export goFoo
+func goFoo() {
+	x := 1
+	for i := 0; i < 10000; i++ {
+		// variadic call mallocs + writes to 
+		variadic(x, x, x)
+		if x != 1 {
+			panic("bad x")
+		}
+	}
+}
+
+func variadic(x ...interface{}) {}
+
+func TestBlocking(t *testing.T) {
+	c := make(chan int)
+	go func() {
+		for i := 0; i < 10; i++ {
+			c <- <-c
+		}
+	}()
+	nestedCall(func(){
+		for i := 0; i < 10; i++ {
+			c <- i
+			if j := <-c; j != i {
+				t.Errorf("out of sync %d != %d", j, i)
+			}
+		}
+	})
+}

misc/cgo/test/callback_c.c

@@ -0,0 +1,12 @@
+// Copyright 2011 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.
+
+#include <sys/types.h>
+#include "_cgo_export.h"
+
+void
+callback(void *f)
+{
+	goCallback(f);
+}

misc/cgo/test/cgo_test.go

@@ -0,0 +1,6 @@
+package cgotest
+
+// dummy file so gotest thinks there are tests.
+// the actual tests are in the main go files, next
+// to the code they test.
+

misc/cgo/stdio/test1.go renamed to misc/cgo/test/issue1222.go

@@ -4,7 +4,7 @@
 
 // This file contains test cases for cgo.
 
-package stdio
+package cgotest
 
 /*
 // issue 1222

misc/cgo/test/issue1328.go

@@ -0,0 +1,30 @@
+// Copyright 2011 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 cgotest
+
+import "testing"
+
+// extern void BackIntoGo(void);
+// void IntoC() { BackIntoGo(); }
+import "C"
+
+//export BackIntoGo
+func BackIntoGo() {
+	x := 1
+
+	for i := 0; i < 10000; i++ {
+		xvariadic(x)
+		if x != 1 {
+			panic("x is not 1?")
+		}
+	}
+}
+
+func xvariadic(x ...interface{}) {
+}
+
+func Test1328(t *testing.T) {
+	C.IntoC()
+}