Support cgo export on amd64.

R=rsc
CC=golang-dev
https://golang.org/cl/857045

src/libcgo/amd64.S

@@ -43,3 +43,39 @@ EXT(crosscall_amd64):
 	popq %rbp
 	popq %rbx
 	ret
+
+/*
+ * void crosscall2(void (*fn)(void*, int32), void *arg, int32 argsize)
+ *
+ * Save registers and call fn with two arguments.  fn is a Go function
+ * which takes parameters on the stack rather than in registers.
+ */
+.globl EXT(crosscall2)
+EXT(crosscall2):
+	subq  $0x58, %rsp	/* keeps stack pointer 32-byte aligned */
+	movq  %rbx, 0x10(%rsp)
+	movq  %rbp, 0x18(%rsp)
+	movq  %r12, 0x20(%rsp)
+	movq  %r13, 0x28(%rsp)
+	movq  %r14, 0x30(%rsp)
+	movq  %r15, 0x38(%rsp)
+
+	movq  %rdi, %r12	/* fn */
+	movq  %rsi, 0(%rsp)	/* arg */
+	movq  %rdx, 8(%rsp)	/* argsize (includes padding) */
+
+	leaq  0x40(%rsp), %rdi
+	call  EXT(libcgo_get_scheduler)
+	movq  0x40(%rsp), %r14	/* m */
+	movq  0x48(%rsp), %r15	/* g */
+
+	call *%r12
+
+	movq  0x10(%rsp), %rbx
+	movq  0x18(%rsp), %rbp
+	movq  0x20(%rsp), %r12
+	movq  0x28(%rsp), %r13
+	movq  0x30(%rsp), %r14
+	movq  0x38(%rsp), %r15
+	addq  $0x58, %rsp
+	ret

src/libcgo/darwin_amd64.c

@@ -7,9 +7,19 @@
 
 static void* threadentry(void*);
 
+static pthread_key_t km, kg;
+
 void
 initcgo(void)
 {
+	if(pthread_key_create(&km, nil) < 0) {
+		fprintf(stderr, "libcgo: pthread_key_create failed\n");
+		abort();
+	}
+	if(pthread_key_create(&kg, nil) < 0) {
+		fprintf(stderr, "libcgo: pthread_key_create failed\n");
+		abort();
+	}
 }
 
 void
@@ -44,3 +54,25 @@ threadentry(void *v)
 	crosscall_amd64(ts.m, ts.g, ts.fn);
 	return nil;
 }
+
+void
+libcgo_set_scheduler(void *m, void *g)
+{
+	pthread_setspecific(km, m);
+	pthread_setspecific(kg, g);
+}
+
+struct get_scheduler_args {
+	void *m;
+	void *g;
+};
+
+void libcgo_get_scheduler(struct get_scheduler_args *)
+  __attribute__ ((visibility("hidden")));
+
+void
+libcgo_get_scheduler(struct get_scheduler_args *p)
+{
+	p->m = pthread_getspecific(km);
+	p->g = pthread_getspecific(kg);
+}

src/libcgo/freebsd_amd64.c

@@ -47,3 +47,28 @@ threadentry(void *v)
 	crosscall_amd64(ts.m, ts.g, ts.fn);
 	return nil;
 }
+
+static __thread void *libcgo_m;
+static __thread void *libcgo_g;
+
+void
+libcgo_set_scheduler(void *m, void *g)
+{
+	libcgo_m = m;
+	libcgo_g = g;
+}
+
+struct get_scheduler_args {
+	void *m;
+	void *g;
+};
+
+void libcgo_get_scheduler(struct get_scheduler_args *)
+  __attribute__ ((visibility("hidden")));
+
+void
+libcgo_get_scheduler(struct get_scheduler_args *p)
+{
+	p->m = libcgo_m;
+	p->g = libcgo_g;
+}

src/libcgo/linux_amd64.c

@@ -44,3 +44,28 @@ threadentry(void *v)
 	crosscall_amd64(ts.m, ts.g, ts.fn);
 	return nil;
 }
+
+static __thread void *libcgo_m;
+static __thread void *libcgo_g;
+
+void
+libcgo_set_scheduler(void *m, void *g)
+{
+	libcgo_m = m;
+	libcgo_g = g;
+}
+
+struct get_scheduler_args {
+	void *m;
+	void *g;
+};
+
+void libcgo_get_scheduler(struct get_scheduler_args *)
+  __attribute__ ((visibility("hidden")));
+
+void
+libcgo_get_scheduler(struct get_scheduler_args *p)
+{
+	p->m = libcgo_m;
+	p->g = libcgo_g;
+}

src/pkg/runtime/amd64/asm.s

@@ -276,14 +276,13 @@ TEXT jmpdefer(SB), 7, $0
 // Save g and m across the call,
 // since the foreign code might reuse them.
 TEXT runcgo(SB),7,$32
-	// Save old registers.
-	MOVQ	fn+0(FP),AX
-	MOVQ	arg+8(FP),DI	// DI = first argument in AMD64 ABI
+	MOVQ	fn+0(FP), R12
+	MOVQ	arg+8(FP), R13
 	MOVQ	SP, CX
 
 	// Figure out if we need to switch to m->g0 stack.
-	MOVQ	m_g0(m), R8
-	CMPQ	R8, g
+	MOVQ	m_g0(m), SI
+	CMPQ	SI, g
 	JEQ	2(PC)
 	MOVQ	(m_sched+gobuf_sp)(m), SP
 
@@ -293,7 +292,17 @@ TEXT runcgo(SB),7,$32
 	MOVQ	g, 24(SP)	// save old g, m, SP
 	MOVQ	m, 16(SP)
 	MOVQ	CX, 8(SP)
-	CALL	AX
+
+	// Save g and m values for a potential callback.  The callback
+	// will start running with on the g0 stack and as such should
+	// have g set to m->g0.
+	MOVQ	m, DI		// DI = first argument in AMD64 ABI
+				// SI, second argument, set above
+	MOVQ	libcgo_set_scheduler(SB), BX
+	CALL	BX
+
+	MOVQ	R13, DI		// DI = first argument in AMD64 ABI
+	CALL	R12
 
 	// Restore registers, stack pointer.
 	MOVQ	16(SP), m
@@ -301,6 +310,32 @@ TEXT runcgo(SB),7,$32
 	MOVQ	8(SP), SP
 	RET
 
+// runcgocallback(G *g1, void* sp, void (*fn)(void))
+// Switch to g1 and sp, call fn, switch back.  fn's arguments are on
+// the new stack.
+TEXT runcgocallback(SB),7,$48
+	MOVQ	g1+0(FP), DX
+	MOVQ	sp+8(FP), AX
+	MOVQ	fp+16(FP), BX
+
+	MOVQ	DX, g
+
+	// We are running on m's scheduler stack.  Save current SP
+	// into m->sched.sp so that a recursive call to runcgo doesn't
+	// clobber our stack, and also so that we can restore
+	// the SP when the call finishes.  Reusing m->sched.sp
+	// for this purpose depends on the fact that there is only
+	// one possible gosave of m->sched.
+	MOVQ	SP, (m_sched+gobuf_sp)(m)
+
+	// Set new SP, call fn
+	MOVQ	AX, SP
+	CALL	BX
+
+	// Restore old SP, return
+	MOVQ	(m_sched+gobuf_sp)(m), SP
+	RET
+
 // check that SP is in range [g->stackbase, g->stackguard)
 TEXT stackcheck(SB), 7, $0
 	CMPQ	g_stackbase(g), SP
@@ -337,3 +372,4 @@ TEXT getcallersp(SB),7,$0
 	MOVQ	sp+0(FP), AX
 	RET
 
+GLOBL libcgo_set_scheduler(SB), $8