[downstream patch FYI] workaround stale frame_info * (PR 13866)

Jan Kratochvil
2012-04-04T19:14:53Z

Hi,

I did not look at which commit caused this regression but apparently it was
introduced at least with multi-inferiors.

I understand this fix is not right fix of the crash; but in most GDB cases one
does not use multi-inferior so why to regress single-inferior by it.
Some more simple solutions still fix the single-inferior mode but they
regressed the multi-inferior mode
gdb.threads/no-unwaited-for-left.exp
gdb.multi/base.exp
so I had to put there that sorting magic.

With proper C++ sanity check of stale live frame_info references the testcase
would be simple without the "frame_garbage_collection" reproducer below.
It is also reproducible just with valgrind but regularly running the whole
testsuite under valgrind I did not find feasible.

No regressions on {x86_64,x86_64-m32,i686}-fedora17-linux-gnu.

Thanks,
Jan

gdb/
2012-04-04 Jan Kratochvil <jan.kratochvil@redhat.com>

Workaround PR backtrace/13866.
* 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)
void
switch_to_program_space_and_thread (struct program_space *pspace)
{
- struct inferior *inf;
+ struct inferior *inf = current_inferior ();

- inf = find_inferior_for_program_space (pspace);
+ if (inf->pspace != pspace)
+ inf = find_inferior_for_program_space (pspace);
if (inf != NULL)
{
- struct thread_info *tp;
+ struct thread_info *tp, *current_tp = NULL;
+
+ if (ptid_get_pid (inferior_ptid) == inf->pid)
+ current_tp = find_thread_ptid (inferior_ptid);

tp = any_live_thread_of_process (inf->pid);
if (tp != NULL)
{
- switch_to_thread (tp->ptid);
+ /* 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))
+ 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;
}