[Bug tdep/29868] [gdb/tdep, s390x] breakpoint.c:5784: internal-error: bpstat_stop_status_nowatch: Assertion `!target_stopped_by_watchpoint ()'

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29868

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arnez at linux dot ibm.com,
                   |                            |ulrich.weigand at de dot ibm.com
          Component|gdb                         |tdep
            Summary|[gdb, s390x]                |[gdb/tdep, s390x]
                   |breakpoint.c:5784:          |breakpoint.c:5784:
                   |internal-error:             |internal-error:
                   |bpstat_stop_status_nowatch: |bpstat_stop_status_nowatch:
                   |Assertion                   |Assertion
                   |`!target_stopped_by_watchpo |`!target_stopped_by_watchpo
                   |int ()'                     |int ()'

--- Comment #2 from Tom de Vries <vries at gcc dot gnu.org> ---
I've added some code for debugging:
...
diff --git a/gdb/s390-linux-nat.c b/gdb/s390-linux-nat.c
index 96833e804e9..654a62545f3 100644
--- a/gdb/s390-linux-nat.c
+++ b/gdb/s390-linux-nat.c
@@ -602,6 +602,9 @@ s390_linux_nat_target::low_forget_process (pid_t pid)
     }
 }

+static void
+s390_show_debug_regs (int tid, const char *where);
+
 /* linux_nat_new_fork hook.   */

 void
@@ -625,6 +628,12 @@ s390_linux_nat_target::low_new_fork (struct lwp_info
*parent, pid_t child_pid)

   child_state->watch_areas = parent_state->watch_areas;
   child_state->break_areas = parent_state->break_areas;
+
+  if (show_debug_regs)
+    {
+      s390_show_debug_regs (parent_pid, "fork -- parent");
+      s390_show_debug_regs (child_pid, "fork -- child");
+    }
 }

 /* Dump PER state.  */
@@ -656,6 +665,10 @@ s390_show_debug_regs (int tid, const char *where)
                per_info.lowcore.words.perc_atmid,
                per_info.lowcore.words.address,
                per_info.lowcore.words.access_id);
+
+  int result = (per_info.lowcore.bits.perc_storage_alteration == 1
+                && per_info.lowcore.bits.perc_store_real_address == 0);
+  debug_printf ("  stopped_by_watchpoint: %d\n", result);
 }

 bool
@@ -688,6 +701,8 @@ s390_linux_nat_target::stopped_by_watchpoint ()
       memset (&per_lowcore, 0, sizeof (per_lowcore));
       if (ptrace (PTRACE_POKEUSR_AREA, s390_inferior_tid (), &parea, 0) < 0)
        perror_with_name (_("Couldn't clear watchpoint status"));
+      if (show_debug_regs)
+       s390_show_debug_regs (s390_inferior_tid (), "clear");
     }

   return result;
...
and then get the following log:
...
$ gdbh -q -batch -ex "set trace-commands on" -x gdb.in
+file
/suse/tdevries/gdb/build/s390x/gdb/testsuite/outputs/gdb.threads/watchpoint-fork/watchpoint-fork-parent-st
+set follow-fork-mode parent
+start
Temporary breakpoint 1 at 0x1000810: file
/suse/tdevries/gdb/src/gdb/testsuite/gdb.threads/watchpoint-fork-st.c, line 49.

Temporary breakpoint 1, main () at
/suse/tdevries/gdb/src/gdb/testsuite/gdb.threads/watchpoint-fork-st.c:49
49        marker ();
+watch var
Hardware watchpoint 2: var
+break marker
Breakpoint 3 at 0x10007da: file
/suse/tdevries/gdb/src/gdb/testsuite/gdb.threads/watchpoint-fork-st.c, line 33.
+info break
Num     Type           Disp Enb Address            What
2       hw watchpoint  keep y                      var
3       breakpoint     keep y   0x00000000010007da in marker at
/suse/tdevries/gdb/src/gdb/testsuite/gdb.threads/watchpoint-fork-st.c:33
+maint set show-debug-regs 1
+continue
PER (debug) state for 55488 -- resume
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 40f0  address: 10006a4  PAID: 0
  stopped_by_watchpoint: 0
PER (debug) state for 55488 -- stop
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 40f0  address: 10006a4  PAID: 0
  stopped_by_watchpoint: 0

Breakpoint 3, marker () at
/suse/tdevries/gdb/src/gdb/testsuite/gdb.threads/watchpoint-fork-st.c:33
33      }
+continue
PER (debug) state for 55488 -- resume
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 40f0  address: 10006a4  PAID: 0
  stopped_by_watchpoint: 0
PER (debug) state for 55488 -- stop
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 40f0  address: 10006a4  PAID: 0
  stopped_by_watchpoint: 0
PER (debug) state for 55488 -- stop
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 40f0  address: 10006a4  PAID: 0
  stopped_by_watchpoint: 0
PER (debug) state for 55488 -- stop
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 20f0  address: 1000820  PAID: 0
  stopped_by_watchpoint: 1
PER (debug) state for 55488 -- clear
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 20f0  address: 1000820  PAID: 0
  stopped_by_watchpoint: 1

Hardware watchpoint 2: var

Old value = 0
New value = 1
main () at
/suse/tdevries/gdb/src/gdb/testsuite/gdb.threads/watchpoint-fork-st.c:52
52        forkoff (1);
+continue
PER (debug) state for 55488 -- resume
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 20f0  address: 1000820  PAID: 0
  stopped_by_watchpoint: 1
PER (debug) state for 55488 -- fork -- parent
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 20f0  address: 1000820  PAID: 0
  stopped_by_watchpoint: 1
PER (debug) state for 55490 -- fork -- child
  cr9-11: 0 0 0
  start, end: 0 0
  code/ATMID: 0  address: 0  PAID: 0
  stopped_by_watchpoint: 0
PER (debug) state for 55488 -- stop
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 20f0  address: 1000820  PAID: 0
  stopped_by_watchpoint: 1
PER (debug) state for 55488 -- clear
  cr9-11: 20200000 100203c 100203f
  start, end: 100203c 100203f
  code/ATMID: 20f0  address: 1000820  PAID: 0
  stopped_by_watchpoint: 1
/suse/tdevries/gdb/src/gdb/breakpoint.c:5784: internal-error:
bpstat_stop_status_nowatch: Assertion `!target_stopped_by_watchpoint ()'
failed.
...

So, the watchpoint triggers, and we try to clear the watch point status in
s390_linux_nat_target::stopped_by_watchpoint to make sure that we "Do not
report this watchpoint again".  That doesn't seem to have any effect though,
and when we stop for the fork s390_linux_nat_target::stopped_by_watchpoint
still returns true, causing the assert.

-- 
You are receiving this mail because:
You are on the CC list for the bug.