libmach: more info when memory reads fail on Darwin

R=r
CC=golang-dev
https://golang.org/cl/604043

diff --git a/src/libmach/darwin.c b/src/libmach/darwin.c
index 87fe423defd2141955f4c2d89c2e1724dc65a4aa..feb49c059b57bde274aa651d475823dd72b39695 100644 (file)
--- a/src/libmach/darwin.c
+++ b/src/libmach/darwin.c
@@ -156,7 +156,7 @@ me(kern_return_t r)
 
        for(i=0; i<nelem(macherr); i++){
                if(r == macherr[i].code){
-                       werrstr("%s", macherr[i].name);
+                       werrstr("mach: %s", macherr[i].name);
                        return -1;
                }
        }
@@ -408,8 +408,10 @@ machsegrw(Map *map, Seg *seg, uvlong addr, void *v, uint n, int isr)
        if(isr){
                vm_size_t nn;
                nn = n;
-               if(me(vm_read_overwrite(task, addr, n, (uintptr)v, &nn)) < 0)
+               if(me(vm_read_overwrite(task, addr, n, (uintptr)v, &nn)) < 0) {
+                       fprint(2, "vm_read_overwrite %#llux %d to %p: %r\n", addr, n, v);
                        return -1;
+               }
                return nn;
        }else{
                r = vm_write(task, addr, (uintptr)v, n);