code review 3822041: runtime: implementation of callback functions for Windo...

src/pkg/runtime/windows/thread.c

Index: src/pkg/runtime/windows/thread.c
===================================================================
--- a/src/pkg/runtime/windows/thread.c
+++ b/src/pkg/runtime/windows/thread.c
@@ -168,8 +168,16 @@
 void
 runtime·syscall(StdcallParams *p)
 {
+	G *oldlock;
 	uintptr a;
 
+	/*
+	 * Lock g to m to ensure we stay on the same stack if we do a callback.
+	 */
+	oldlock = m->lockedg;
+	m->lockedg = g;
+	g->lockedm = m;
+
 	runtime·entersyscall();
 	// TODO(brainman): Move calls to SetLastError and GetLastError
 	// to stdcall_raw to speed up syscall.
@@ -178,4 +186,32 @@
 	p->r = (uintptr)runtime·stdcall_raw((void*)p->fn, p->n, p->args);
 	p->err = (uintptr)runtime·stdcall_raw(runtime·GetLastError, 0, &a);
 	runtime·exitsyscall();
+
+	m->lockedg = oldlock;
+	if(oldlock == nil)
+		g->lockedm = nil;
 }
+
+// Call back from windows dll into go.
+void
+runtime·setcallback(byte *code, void *fn, uint32 argsize)
+{
+	byte *p = code;
+
+	// PUSH argsize
+	*p++ = 0x68;
+	*(uint32*)p = argsize;
+	p += 4;
+	// PUSH fn
+	*p++ = 0x68;
+	*(uint32*)p = (uint32)fn;
+	p += 4;
+	// MOV callbackasm, AX
+	void* (*x)(void) = runtime·callbackasm;
+	*p++ = 0xb8;
+	*(uint32*)p = (uint32)x;
+	p += 4;
+	// CALL AX
+	*p++ = 0xff;
+	*p++ = 0xd0;
+}