Do not use address of a local variable to get approximate stack pointer

Use __builtin_frame_address(0), if available, in
GC_call_with_stack_base(), GC_call_with_gc_active() and
GC_do_blocking_inner().

* misc.c (GC_call_with_stack_base): Use APPROX_SP() to set
base.mem_base.
* misc.c [!THREADS] (GC_call_with_gc_active): Use
APPROX_SP(&stacksect.saved_stack_ptr) instead of &stacksect; update
comment.
* pthread_support.c (GC_call_with_gc_active): Likewise.
* misc.c [!THREADS] (GC_do_blocking_inner): Remove d local variable.
* pthread_support.c (GC_do_blocking_inner): Likewise.
* misc.c [!THREADS && !SPARC] (GC_do_blocking_inner): Use
GC_approx_sp() instead of &d to set GC_blocked_sp; remove useless
comment; do not compare GC_blocked_sp to &d in assertion.
* pthread_support.c [GC_PTHREADS && !SN_TARGET_ORBIS
&& !SN_TARGET_PSP2 && DEBUG_THREADS] (GC_start_rtn_prepare_thread): Use
GC_approx_sp() instead of &arg.

misc.c

@@ -2396,7 +2396,7 @@ GC_call_with_stack_base(GC_stack_base_func fn, void *arg)
   struct GC_stack_base base;
   void *result;
 
-  base.mem_base = &base;
+  APPROX_SP((volatile ptr_t *)&base.mem_base);
 #ifdef IA64
   base.reg_base = GC_save_regs_in_stack();
   /* TODO: Unnecessarily flushes register stack,    */
@@ -2437,9 +2437,10 @@ GC_call_with_gc_active(GC_fn_type fn, void *client_data)
 
   /* Adjust our stack bottom pointer (this could happen if    */
   /* GC_get_main_stack_base() is unimplemented or broken for  */
-  /* the platform).                                           */
-  if (HOTTER_THAN(GC_stackbottom, (ptr_t)(&stacksect)))
-    GC_stackbottom = COVERT_DATAFLOW_P(&stacksect);
+  /* the platform).  Note: stacksect variable is reused here. */
+  APPROX_SP((volatile ptr_t *)&stacksect.saved_stack_ptr);
+  if (HOTTER_THAN(GC_stackbottom, stacksect.saved_stack_ptr))
+    GC_stackbottom = stacksect.saved_stack_ptr;
 
   if (GC_blocked_sp == NULL) {
     /* We are not inside GC_do_blocking() - do nothing more.  */
@@ -2484,28 +2485,23 @@ GC_call_with_gc_active(GC_fn_type fn, void *client_data)
 STATIC void
 GC_do_blocking_inner(ptr_t data, void *context)
 {
-  struct blocking_data *d = (struct blocking_data *)data;
-
   UNUSED_ARG(context);
   GC_ASSERT(GC_is_initialized);
   GC_ASSERT(GC_blocked_sp == NULL);
 #  ifdef SPARC
   GC_blocked_sp = GC_save_regs_in_stack();
 #  else
-  /* Save the approximate stack pointer.  */
-  GC_blocked_sp = (ptr_t)&d;
+  GC_blocked_sp = GC_approx_sp();
 #    ifdef IA64
   GC_blocked_register_sp = GC_save_regs_in_stack();
 #    endif
 #  endif
 
-  d->client_data = d->fn(d->client_data);
+  ((struct blocking_data *)data)->client_data /* result */
+      = ((struct blocking_data *)data)
+            ->fn(((struct blocking_data *)data)->client_data);
 
-#  ifdef SPARC
   GC_ASSERT(GC_blocked_sp != NULL);
-#  else
-  GC_ASSERT(GC_blocked_sp == (ptr_t)(&d));
-#  endif
 #  if defined(CPPCHECK)
   GC_noop1_ptr(GC_blocked_sp);
 #  endif

pthread_support.c

@@ -2000,7 +2000,6 @@ do_blocking_leave(GC_thread me, GC_bool topOfStackUnset)
 GC_INNER void
 GC_do_blocking_inner(ptr_t data, void *context)
 {
-  struct blocking_data *d = (struct blocking_data *)data;
   GC_thread me;
   GC_bool topOfStackUnset;
 
@@ -2010,7 +2009,9 @@ GC_do_blocking_inner(ptr_t data, void *context)
   do_blocking_enter(&topOfStackUnset, me);
   READER_UNLOCK_RELEASE();
 
-  d->client_data = d->fn(d->client_data);
+  ((struct blocking_data *)data)->client_data /* result */
+      = ((struct blocking_data *)data)
+            ->fn(((struct blocking_data *)data)->client_data);
 
   /* This will block if the world is stopped. */
   READER_LOCK();
@@ -2162,10 +2163,11 @@ GC_call_with_gc_active(GC_fn_type fn, void *client_data)
   /* GC_get_stack_base() was used which returned GC_SUCCESS). */
   stack_end = crtn->stack_end; /* read of a volatile field */
   GC_ASSERT(stack_end != NULL);
-  if (HOTTER_THAN(stack_end, (ptr_t)(&stacksect))) {
-    crtn->stack_end = (ptr_t)(&stacksect);
+  APPROX_SP((volatile ptr_t *)&stacksect.saved_stack_ptr);
+  if (HOTTER_THAN(stack_end, stacksect.saved_stack_ptr)) {
+    crtn->stack_end = stacksect.saved_stack_ptr;
 #  if defined(I386) && defined(GC_WIN32_THREADS)
-    crtn->initial_stack_base = (ptr_t)(&stacksect);
+    crtn->initial_stack_base = stacksect.saved_stack_ptr;
 #  endif
   }
 
@@ -2595,7 +2597,8 @@ GC_start_rtn_prepare_thread(void *(**pstart)(void *), void **pstart_arg,
 
 #    ifdef DEBUG_THREADS
   GC_log_printf("Starting thread %p, sp= %p\n",
-                (void *)GC_PTHREAD_PTRVAL(pthread_self()), (void *)&arg);
+                (void *)GC_PTHREAD_PTRVAL(pthread_self()),
+                (void *)GC_approx_sp());
 #    endif
   /* If a GC occurs before the thread is registered, that GC will     */
   /* ignore this thread.  That's fine, since it will block trying to  */