[patch] Fix stale tp->step_resume_breakpoint

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

while debugging unrelated issue I got some:
	bpstat_what: unhandled bptype -3735941133 (garbage)

due to a stale memory below.

I did not create a special testcase but it is reproducible with valgrind and
the following code (which is not a minimal reproducer):

Invalid read of size 4
   at: is_hardware_watchpoint (breakpoint.c:1212)
   by: is_watchpoint (breakpoint.c:1223)
   by: bpstat_check_watchpoint (breakpoint.c:3741)
   by: bpstat_stop_status (breakpoint.c:4098)
   by: handle_inferior_event (infrun.c:3898)
   by: wait_for_inferior (infrun.c:2575)
   by: proceed (infrun.c:2106)
   by: step_once (infcmd.c:1031)
   by: step_1 (infcmd.c:880)
   by: stepi_command (infcmd.c:816)
   by: do_cfunc (cli-decode.c:67)
   by: cmd_func (cli-decode.c:1771)
   by: execute_command (top.c:422)
   by: command_loop (top.c:534)
   by: read_command_file (top.c:321)
   by: wrapped_read_command_file (cli-script.c:1592)
   by: catch_exception (exceptions.c:468)
   by: script_from_file (cli-script.c:1622)
   by: source_script_from_stream (cli-cmds.c:557)
   by: source_script_with_search (cli-cmds.c:588)
   by: source_script (cli-cmds.c:598)
   by: catch_command_errors (exceptions.c:534)
   by: captured_main (main.c:886)
   by: catch_errors (exceptions.c:518)
   by: gdb_main (main.c:921)
   by: main (gdb.c:34)
 Address 0xb62d808 is 8 bytes inside a block of size 368 free'd
   at: free (vg_replace_malloc.c:325)
   by: xfree (utils.c:1525)
   by: delete_breakpoint (breakpoint.c:9733)
   by: delete_step_resume_breakpoint (thread.c:88)
   by: delete_step_resume_breakpoint_callback (infrun.c:2339)
   by: iterate_over_threads (thread.c:353)
   by: delete_step_thread_step_resume_breakpoint (infrun.c:2368)
   by: delete_step_thread_step_resume_breakpoint_cleanup (infrun.c:2376)
   by: do_my_cleanups (utils.c:479)
   by: do_cleanups (utils.c:461)
   by: wait_for_inferior (infrun.c:2584)
   by: proceed (infrun.c:2106)
   by: run_inferior_call (infcall.c:378)
   by: call_function_by_hand (infcall.c:804)
   by: evaluate_subexp_standard (eval.c:1816)
   by: evaluate_subexp_c (c-lang.c:1047)
   by: evaluate_subexp (eval.c:76)
   by: evaluate_expression (eval.c:167)
   by: breakpoint_cond_eval (breakpoint.c:3431)
   by: catch_errors (exceptions.c:518)
   by: bpstat_check_breakpoint_conditions (breakpoint.c:3959)
   by: bpstat_stop_status (breakpoint.c:4110)
   by: handle_inferior_event (infrun.c:3898)
   by: wait_for_inferior (infrun.c:2575)
   by: proceed (infrun.c:2106)
   by: step_once (infcmd.c:1031)
   by: step_1 (infcmd.c:880)
   by: stepi_command (infcmd.c:816)
   by: do_cfunc (cli-decode.c:67)
   by: cmd_func (cli-decode.c:1771)
   by: execute_command (top.c:422)
   by: command_loop (top.c:534)
   by: read_command_file (top.c:321)
   by: wrapped_read_command_file (cli-script.c:1592)
   by: catch_exception (exceptions.c:468)
   by: script_from_file (cli-script.c:1622)
   by: source_script_from_stream (cli-cmds.c:557)
   by: source_script_with_search (cli-cmds.c:588)
   by: source_script (cli-cmds.c:598)
   by: catch_command_errors (exceptions.c:534)
   by: captured_main (main.c:886)
   by: catch_errors (exceptions.c:518)
   by: gdb_main (main.c:921)
   by: main (gdb.c:34)

#define _GNU_SOURCE
#include <stdio.h>
#include <signal.h>
#include <pthread.h>
#include <asm/unistd.h>
#include <unistd.h>
#define tgkill(pid, tid, sig) syscall (__NR_tgkill, (pid), (tid), (sig))
#define gettid() syscall (__NR_gettid)
int condA (void) { puts ("condA"); return 1; }
int condB (void) { puts ("condB"); return 1; }
__attribute__((noinline, noclone)) void loop (void)
{
  volatile int i = 0;
  for (;;);
    i = 0;
}
static void *start (void *arg)
{
  for (;;)
    {
      tgkill (getpid (), getpid (), SIGUSR1);
      usleep (10000);
    }
  return arg;
}
int main (void)
{
  pthread_t thread;
  pthread_create (&thread, NULL, start, NULL);
  loop ();
  return 0;
}

file ./1
handle SIGUSR1 print nopass nostop
tb loop
r
disass
b if condA ()
commands
echo A\n
end
stepi
b if condB ()
commands
echo B\n
end
#set debug infrun 1
stepi
stepi
 <-- CTRL-C it here, it keeps scrolling signal deliveries

gcc -o 1 1.c -O2 -Wall -g -pthread
valgrind --db-attach=yes --num-callers=50 ./gdb -nx -x ./1.cmd
x86_64-fedora13-linux-gnu


No regressions on {x86_64,x86_64-m32,i686}-fedora14snapshot-linux-gnu.

A comment is welcome but it seems safe to me.


Thanks,
Jan


gdb/
2010-11-02  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* infrun.c (struct inferior_thread_state) <step_resume_breakpoint>:
	New field.
	(save_inferior_thread_state): Save STEP_RESUME_BREAKPOINT.
	(restore_inferior_thread_state): Restore STEP_RESUME_BREAKPOINT.

--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -6044,6 +6044,7 @@ struct inferior_thread_state
   enum target_signal stop_signal;
   CORE_ADDR stop_pc;
   struct regcache *registers;
+  struct breakpoint *step_resume_breakpoint;
 
   /* Format of SIGINFO or NULL if it is not present.  */
   struct gdbarch *siginfo_gdbarch;
@@ -6096,6 +6097,9 @@ save_inferior_thread_state (void)
 
   inf_state->registers = regcache_dup (regcache);
 
+  inf_state->step_resume_breakpoint = tp->step_resume_breakpoint;
+  tp->step_resume_breakpoint = NULL;
+
   return inf_state;
 }
 
@@ -6127,6 +6131,11 @@ restore_inferior_thread_state (struct inferior_thread_state *inf_state)
     /* NB: The register write goes through to the target.  */
     regcache_cpy (regcache, inf_state->registers);
   regcache_xfree (inf_state->registers);
+
+  /* Check first for stale STEP_RESUME_BREAKPOINT after an infcall.  */
+  gdb_assert (tp->step_resume_breakpoint == NULL);
+  tp->step_resume_breakpoint = inf_state->step_resume_breakpoint;
+
   xfree (inf_state->siginfo_data);
   xfree (inf_state);
 }