runtime: stack copier should handle nil defers without faulting.

fixes #8047

LGTM=rsc
R=golang-codereviews, rsc
CC=golang-codereviews
https://golang.org/cl/101800043

diff --git a/src/pkg/runtime/stack.c b/src/pkg/runtime/stack.c
index d265d4b5008f941bf56cccae56ec6e1122db2066..a5e0f87a466a83957b0773f6dfaa401da201e30c 100644 (file)
--- a/src/pkg/runtime/stack.c
+++ b/src/pkg/runtime/stack.c
@@ -344,6 +344,8 @@ copyabletopsegment(G *gp)
                if(d->argp < cinfo.stk || cinfo.base <= d->argp)
                        break; // a defer for the next segment
                fn = d->fn;
+               if(fn == nil) // See issue 8047
+                       continue;
                f = runtime·findfunc((uintptr)fn->fn);
                if(f == nil)
                        return -1;
@@ -552,13 +554,19 @@ adjustdefers(G *gp, AdjustInfo *adjinfo)
                }
                if(d->argp < adjinfo->oldstk || adjinfo->oldbase <= d->argp)
                        break; // a defer for the next segment
-               f = runtime·findfunc((uintptr)d->fn->fn);
+               fn = d->fn;
+               if(fn == nil) {
+                       // Defer of nil function.  It will panic when run, and there
+                       // aren't any args to adjust.  See issue 8047.
+                       d->argp += adjinfo->delta;
+                       continue;
+               }
+               f = runtime·findfunc((uintptr)fn->fn);
                if(f == nil)
                        runtime·throw("can't adjust unknown defer");
                if(StackDebug >= 4)
                        runtime·printf("  checking defer %s\n", runtime·funcname(f));
                // Defer's FuncVal might be on the stack
-               fn = d->fn;
                if(adjinfo->oldstk <= (byte*)fn && (byte*)fn < adjinfo->oldbase) {
                        if(StackDebug >= 3)
                                runtime·printf("    adjust defer fn %s\n", runtime·funcname(f));