re PR go/65349 (go tool crashes, can't compile go code on 32bit linux systems)

PR go/65349
runtime: Don't call malloc from __go_file_line callback.

When crashing, we call runtime_printcreatedby which calls
__go_file_line which used to call the Go malloc.  If we are
crashing due to a signal due to heap corruption of some sort,
the GO malloc lock might already be held, leading to a crash
within a crash.  Avoid that by assuming that the libbacktrace
strings will stick around, as we already do in go-callers.c.

From-SVN: r221291

libgo/runtime/go-caller.c

@@ -37,36 +37,12 @@ callback (void *data, uintptr_t pc __attribute__ ((unused)),
 {
   struct caller *c = (struct caller *) data;
 
-  if (function == NULL)
+  /* The libbacktrace library says that these strings might disappear,
-    {
+     but with the current implementation they won't.  We can't easily
-      c->fn.str = NULL;
+     allocate memory here, so for now assume that we can save a
-      c->fn.len = 0;
+     pointer to the strings.  */
-    }
+  c->fn = runtime_gostringnocopy ((const byte *) function);
-  else
+  c->file = runtime_gostringnocopy ((const byte *) filename);
-    {
-      byte *s;
-
-      c->fn.len = __builtin_strlen (function);
-      s = runtime_malloc (c->fn.len);
-      __builtin_memcpy (s, function, c->fn.len);
-      c->fn.str = s;
-    }
-
-  if (filename == NULL)
-    {
-      c->file.str = NULL;
-      c->file.len = 0;
-    }
-  else
-    {
-      byte *s;
-
-      c->file.len = __builtin_strlen (filename);
-      s = runtime_malloc (c->file.len);
-      __builtin_memcpy (s, filename, c->file.len);
-      c->file.str = s;
-    }
-
   c->line = lineno;
 
   return 0;