9 files changed, 95 insertions, 0 deletions
diff --git a/src/pkg/runtime/asm_386.s b/src/pkg/runtime/asm_386.s
index 6bbec30638..da2290210a 100644
--- a/src/pkg/runtime/asm_386.s
+++ b/src/pkg/runtime/asm_386.s
@@ -425,6 +425,14 @@ TEXT runtime·cgocallback(SB),7,$12
 	// Save current m->g0->sched.sp on stack and then set it to SP.
 	get_tls(CX)
 	MOVL	m(CX), BP
+
+	// If m is nil, it is almost certainly because we have been called
+	// on a thread that Go did not create.  We're going to crash as
+	// soon as we try to use m; instead, try to print a nice error and exit.
+	CMPL	BP, $0
+	JNE 2(PC)
+	CALL	runtime·badcallback(SB)
+
 	MOVL	m_g0(BP), SI
 	PUSHL	(g_sched+gobuf_sp)(SI)
 	MOVL	SP, (g_sched+gobuf_sp)(SI)
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index 2ea87a779f..392ad8c87f 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -471,6 +471,14 @@ TEXT runtime·cgocallback(SB),7,$24
 	// Save current m->g0->sched.sp on stack and then set it to SP.
 	get_tls(CX)
 	MOVQ	m(CX), BP
+	
+	// If m is nil, it is almost certainly because we have been called
+	// on a thread that Go did not create.  We're going to crash as
+	// soon as we try to use m; instead, try to print a nice error and exit.
+	CMPQ	BP, $0
+	JNE 2(PC)
+	CALL	runtime·badcallback(SB)
+
 	MOVQ	m_g0(BP), SI
 	PUSHQ	(g_sched+gobuf_sp)(SI)
 	MOVQ	SP, (g_sched+gobuf_sp)(SI)
diff --git a/src/pkg/runtime/thread_darwin.c b/src/pkg/runtime/thread_darwin.c
index 556fb67e84..bbcdf05ef0 100644
--- a/src/pkg/runtime/thread_darwin.c
+++ b/src/pkg/runtime/thread_darwin.c
@@ -477,3 +477,13 @@ runtime·setprof(bool on)
 	else
 		runtime·sigprocmask(SIG_BLOCK, &sigset_prof, nil);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	runtime·write(2, badcallback, sizeof badcallback - 1);
+}
diff --git a/src/pkg/runtime/thread_freebsd.c b/src/pkg/runtime/thread_freebsd.c
index 77e8bb3dac..b848cbadd4 100644
--- a/src/pkg/runtime/thread_freebsd.c
+++ b/src/pkg/runtime/thread_freebsd.c
@@ -195,3 +195,13 @@ runtime·setprof(bool on)
 {
 	USED(on);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	runtime·write(2, badcallback, sizeof badcallback - 1);
+}
diff --git a/src/pkg/runtime/thread_linux.c b/src/pkg/runtime/thread_linux.c
index 6b428440e0..af765d53b9 100644
--- a/src/pkg/runtime/thread_linux.c
+++ b/src/pkg/runtime/thread_linux.c
@@ -255,3 +255,13 @@ runtime·setprof(bool on)
 {
 	USED(on);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	runtime·write(2, badcallback, sizeof badcallback - 1);
+}
diff --git a/src/pkg/runtime/thread_netbsd.c b/src/pkg/runtime/thread_netbsd.c
index 62e133c449..40e4f6ce1c 100644
--- a/src/pkg/runtime/thread_netbsd.c
+++ b/src/pkg/runtime/thread_netbsd.c
@@ -213,3 +213,13 @@ runtime·setprof(bool on)
 {
 	USED(on);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	runtime·write(2, badcallback, sizeof badcallback - 1);
+}
diff --git a/src/pkg/runtime/thread_openbsd.c b/src/pkg/runtime/thread_openbsd.c
index bee0c5755f..e4f95988b0 100644
--- a/src/pkg/runtime/thread_openbsd.c
+++ b/src/pkg/runtime/thread_openbsd.c
@@ -213,3 +213,13 @@ runtime·setprof(bool on)
 {
 	USED(on);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	runtime·write(2, badcallback, sizeof badcallback - 1);
+}
diff --git a/src/pkg/runtime/thread_plan9.c b/src/pkg/runtime/thread_plan9.c
index aaed5050bb..4ca01b0e66 100644
--- a/src/pkg/runtime/thread_plan9.c
+++ b/src/pkg/runtime/thread_plan9.c
@@ -247,3 +247,13 @@ runtime·setprof(bool on)
 {
 	USED(on);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	runtime·pwrite(2, badcallback, sizeof badcallback - 1, -1LL);
+}
diff --git a/src/pkg/runtime/thread_windows.c b/src/pkg/runtime/thread_windows.c
index 1147a05e6a..e75e0c1569 100644
--- a/src/pkg/runtime/thread_windows.c
+++ b/src/pkg/runtime/thread_windows.c
@@ -422,3 +422,22 @@ runtime·setprof(bool on)
 {
 	USED(on);
 }
+
+static int8 badcallback[] = "runtime: cgo callback on thread not created by Go.\n";
+
+// This runs on a foreign stack, without an m or a g.  No stack split.
+#pragma textflag 7
+void
+runtime·badcallback(void)
+{
+	uint32 written;
+
+	runtime·stdcall(
+		runtime·WriteFile, 5,
+		runtime·stdcall(runtime·GetStdHandle, 1, (uintptr)-12), // stderr
+		badcallback,
+		(uintptr)(sizeof badcallback - 1),
+		&written,
+		nil
+	);
+}