runtime: arrange to show a few local variables when cgoCheckUnknownPointer panics

For #13934.

Change-Id: Id399e35598def96f8bb89b9fcd1bf14ee06e2e62
Reviewed-on: https://go-review.googlesource.com/18612
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
index 9710c418b22041d16186e40634305f038e28f6f6..3b395fb8cdd7f62cd0431948a9c5a7811a8dd192 100644 (file)
--- a/src/runtime/cgocall.go
+++ b/src/runtime/cgocall.go
@@ -498,7 +498,8 @@ func cgoCheckArg(t *_type, p unsafe.Pointer, indir, top bool, msg string) {
 // cgoCheckUnknownPointer is called for an arbitrary pointer into Go
 // memory.  It checks whether that Go memory contains any other
 // pointer into Go memory.  If it does, we panic.
-func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) {
+// The return values are unused but useful to see in panic tracebacks.
+func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) (base, i uintptr) {
        if cgoInRange(p, mheap_.arena_start, mheap_.arena_used) {
                if !inheap(uintptr(p)) {
                        // This pointer is either to a stack or to an
@@ -508,12 +509,13 @@ func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) {
                        panic(errorString("cgo argument has invalid Go pointer"))
                }
 
-               base, hbits, span := heapBitsForObject(uintptr(p), 0, 0)
+               b, hbits, span := heapBitsForObject(uintptr(p), 0, 0)
+               base = b
                if base == 0 {
                        return
                }
                n := span.elemsize
-               for i := uintptr(0); i < n; i += sys.PtrSize {
+               for i = uintptr(0); i < n; i += sys.PtrSize {
                        bits := hbits.bits()
                        if i >= 2*sys.PtrSize && bits&bitMarked == 0 {
                                // No more possible pointers.
@@ -539,6 +541,8 @@ func cgoCheckUnknownPointer(p unsafe.Pointer, msg string) {
                // In the text or noptr sections, we know that the
                // pointer does not point to a Go pointer.
        }
+
+       return
 }
 
 // cgoIsGoPointer returns whether the pointer is a Go pointer--a