3 files changed, 21 insertions, 6 deletions

diff --git a/src/pkg/runtime/cgocall.c b/src/pkg/runtime/cgocall.c
index 7b2ec26f3..75d3850ef 100644
--- a/src/pkg/runtime/cgocall.c
+++ b/src/pkg/runtime/cgocall.c
@@ -234,14 +234,18 @@ void runtime·cgocallbackg1(void);
 void
 runtime·cgocallbackg(void)
 {
+	uintptr pc, sp;
+
 	if(g != m->curg) {
 		runtime·prints("runtime: bad g in cgocallback");
 		runtime·exit(2);
 	}
 
+	pc = g->syscallpc;
+	sp = g->syscallsp;
 	runtime·exitsyscall();	// coming out of cgo call
 	runtime·cgocallbackg1();
-	runtime·entersyscall();	// going back to cgo call
+	runtime·reentersyscall((void*)pc, sp);	// going back to cgo call
 }
 
 void
diff --git a/src/pkg/runtime/proc.c b/src/pkg/runtime/proc.c
index 914a02e0b..de4f70153 100644
--- a/src/pkg/runtime/proc.c
+++ b/src/pkg/runtime/proc.c
@@ -1499,14 +1499,14 @@ save(void *pc, uintptr sp)
 // entersyscall is going to return immediately after.
 #pragma textflag NOSPLIT
 void
-·entersyscall(int32 dummy)
+runtime·reentersyscall(void *pc, uintptr sp)
 {
 	// Disable preemption because during this function g is in Gsyscall status,
 	// but can have inconsistent g->sched, do not let GC observe it.
 	m->locks++;
 
 	// Leave SP around for GC and traceback.
-	save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+	save(pc, sp);
 	g->syscallsp = g->sched.sp;
 	g->syscallpc = g->sched.pc;
 	g->syscallstack = g->stackbase;
@@ -1525,7 +1525,7 @@ void
 			runtime·notewakeup(&runtime·sched.sysmonnote);
 		}
 		runtime·unlock(&runtime·sched);
-		save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+		save(pc, sp);
 	}
 
 	m->mcache = nil;
@@ -1538,7 +1538,7 @@ void
 				runtime·notewakeup(&runtime·sched.stopnote);
 		}
 		runtime·unlock(&runtime·sched);
-		save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+		save(pc, sp);
 	}
 
 	// Goroutines must not split stacks in Gsyscall status (it would corrupt g->sched).
@@ -1548,6 +1548,13 @@ void
 	m->locks--;
 }
 
+#pragma textflag NOSPLIT
+void
+·entersyscall(int32 dummy)
+{
+	runtime·reentersyscall(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
+}
+
 // The same as runtime·entersyscall(), but with a hint that the syscall is blocking.
 #pragma textflag NOSPLIT
 void
@@ -1588,10 +1595,13 @@ void
 // from the low-level system calls used by the runtime.
 #pragma textflag NOSPLIT
 void
-runtime·exitsyscall(void)
+·exitsyscall(int32 dummy)
 {
 	m->locks++;  // see comment in entersyscall
 
+	if(runtime·getcallersp(&dummy) > g->syscallsp)
+		runtime·throw("exitsyscall: syscall frame is no longer valid");
+
 	if(g->isbackground)  // do not consider blocked scavenger for deadlock detection
 		incidlelocked(-1);
 
diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index 511550378..42fb3a47d 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -921,6 +921,7 @@ M*	runtime·newm(void);
 void	runtime·goexit(void);
 void	runtime·asmcgocall(void (*fn)(void*), void*);
 void	runtime·entersyscall(void);
+void	runtime·reentersyscall(void*, uintptr);
 void	runtime·entersyscallblock(void);
 void	runtime·exitsyscall(void);
 G*	runtime·newproc1(FuncVal*, byte*, int32, int32, void*);