[release-branch.go1.3] runtime: revise CL 105140044 (defer nil) to work on Windows

rsc · rsc · commit 64de40a55106 · 2014-06-12T21:52:52.000-04:00
««« CL 105120044 / 824ea5943ba8 runtime: revise CL 105140044 (defer nil) to work on Windows It appears that something about Go on Windows cannot handle the fault cause by a jump to address 0. The way Go represents and calls functions, this never happened at all, until CL 105140044. This CL changes the code added in CL 105140044 to make jump to 0 impossible once again. Fixes #8047. (again, on Windows) TBR=bradfitz R=golang-codereviews, dave CC=adg, golang-codereviews, iant, r https://golang.org/cl/105120044 »»» LGTM=bradfitz R=golang-codereviews, bradfitz, alex.brainman CC=adg, golang-codereviews https://golang.org/cl/108890045
diff --git a/src/pkg/runtime/stack.c b/src/pkg/runtime/stack.c
@@ -9,6 +9,7 @@
 #include "funcdata.h"
 #include "typekind.h"
 #include "type.h"
+#include "../../cmd/ld/textflag.h"
 
 enum
 {
@@ -851,16 +852,24 @@ runtime·newstack(void)
 	*(int32*)345 = 123;	// never return
 }
 
+#pragma textflag NOSPLIT
+void
+runtime·nilfunc(void)
+{
+	*(byte*)0 = 0;
+}
+
 // adjust Gobuf as if it executed a call to fn
 // and then did an immediate gosave.
 void
 runtime·gostartcallfn(Gobuf *gobuf, FuncVal *fv)
 {
 	void *fn;
 
-	fn = nil;
 	if(fv != nil)
 		fn = fv->fn;
+	else
+		fn = runtime·nilfunc;
 	runtime·gostartcall(gobuf, fn, fv);
 }
 
