Workaround crashes from stale frame_info pointer (BZ 804256).

gdb-stale-frame_info.patch

@@ -33,9 +33,11 @@ gdb/
 	* progspace.c (switch_to_program_space_and_thread): Try not to call
 	switch_to_thread.
 
---- a/gdb/progspace.c
-+++ b/gdb/progspace.c
-@@ -481,17 +481,28 @@ save_current_space_and_thread (void)
+Index: gdb-7.3.50.20110722/gdb/progspace.c
+===================================================================
+--- gdb-7.3.50.20110722.orig/gdb/progspace.c	2011-01-05 23:22:50.000000000 +0100
++++ gdb-7.3.50.20110722/gdb/progspace.c	2012-04-04 23:07:16.329038403 +0200
+@@ -480,17 +480,36 @@ save_current_space_and_thread (void)
  void
  switch_to_program_space_and_thread (struct program_space *pspace)
  {
@@ -57,118 +59,22 @@ gdb/
        if (tp != NULL)
  	{
 -	  switch_to_thread (tp->ptid);
++	  /* thread.c */
++	  enum thread_state
++	  {
++	    THREAD_STOPPED,
++	    THREAD_RUNNING,
++	    THREAD_EXITED,
++	  };
++
 +	  /* Prefer primarily thread not THREAD_EXITED and secondarily thread
 +	     not EXECUTING.  */
 +	  if (current_tp == NULL
-+	      || (tp->state != THREAD_EXITED
-+		  && current_tp->state == THREAD_EXITED)
-+	      || (!tp->executing && current_tp->executing))
++	      || (tp->state_ != THREAD_EXITED
++		  && current_tp->state_ == THREAD_EXITED)
++	      || (!tp->executing_ && current_tp->executing_))
 +	    switch_to_thread (tp->ptid);
 +
  	  /* Switching thread switches pspace implicitly.  We're
  	     done.  */
  	  return;
-
-
-Reproducer with:
-./gdb -nx ~/t/thread -ex 'b 24' -ex r -ex 'until 25'
-Breakpoint 1, main () at /home/jkratoch/t/thread.c:24
-24	  v++;
-Segmentation fault (core dumped)
-
-#include <pthread.h>
-#include <assert.h>
-#include <unistd.h>
-
-static int v;
-
-static void *start (void *arg)
-{
-  v++;
-  v++;
-  v++;
-  v++;
-  sleep (100);
-  return arg;
-}
-
-int main (void)
-{
-  pthread_t thread1;
-  int i;
-
-  i = pthread_create (&thread1, NULL, start, NULL);
-  assert (i == 0);
-  v++;
-  v++;
-  v++;
-  v++;
-  i = pthread_join (thread1, NULL);
-  assert (i == 0);
-
-  return 0;
-}
-### --- a/gdb/frame.c
-### +++ b/gdb/frame.c
-### @@ -1522,12 +1522,30 @@ frame_observer_target_changed (struct target_ops *target)
-###    reinit_frame_cache ();
-###  }
-###  
-### +typedef struct obstack obstack_s;
-### +DEF_VEC_O (obstack_s);
-### +static VEC (obstack_s) *frame_poison_vec;
-### +
-### +void frame_garbage_collection (void);
-### +void
-### +frame_garbage_collection (void)
-### +{
-### +  struct obstack *obstack_p;
-### +  int ix;
-### +
-### +  for (ix = 0; VEC_iterate (obstack_s, frame_poison_vec, ix, obstack_p); ix++)
-### +    obstack_free (obstack_p, 0);
-### +
-### +  VEC_free (obstack_s, frame_poison_vec);
-### +  frame_poison_vec = NULL;
-### +}
-### +
-###  /* Flush the entire frame cache.  */
-###  
-###  void
-###  reinit_frame_cache (void)
-###  {
-### -  struct frame_info *fi;
-### +  struct frame_info *fi, *fi_prev;
-###  
-###    /* Tear down all frame caches.  */
-###    for (fi = current_frame; fi != NULL; fi = fi->prev)
-### @@ -1538,8 +1556,14 @@ reinit_frame_cache (void)
-###  	fi->base->unwind->dealloc_cache (fi, fi->base_cache);
-###      }
-###  
-### +  for (fi = current_frame; fi != NULL; fi = fi_prev)
-### +    {
-### +      fi_prev = fi->prev;
-### +      memset (fi, 0, sizeof (*fi));
-### +    }
-### +  VEC_safe_push (obstack_s, frame_poison_vec, &frame_cache_obstack);
-### +
-###    /* Since we can't really be sure what the first object allocated was.  */
-### -  obstack_free (&frame_cache_obstack, 0);
-###    obstack_init (&frame_cache_obstack);
-###  
-###    if (current_frame != NULL)
-### --- a/gdb/top.c
-### +++ b/gdb/top.c
-### @@ -359,6 +359,11 @@ prepare_execute_command (void)
-###    if (non_stop)
-###      target_dcache_invalidate ();
-###  
-### +  {
-### +    extern void frame_garbage_collection (void);
-### +    frame_garbage_collection ();
-### +  }
-### +
-###    return cleanup;
-###  }
-###