Consecutive step-overs trigger internal error.
If a thread trips on a breakpoint that needs stepping over just after
finishing a step over, GDB currently fails an assertion. This is a
regression caused by the "Handle multiple step-overs." patch
(99619beac6) at
https://sourceware.org/ml/gdb-patches/2014-02/msg00765.html.
(gdb) x /4i $pc
=> 0x400540 <main+4>: movl $0x0,0x2003da(%rip) # 0x600924 <i>
0x40054a <main+14>: movl $0x1,0x2003d0(%rip) # 0x600924 <i>
0x400554 <main+24>: movl $0x2,0x2003c6(%rip) # 0x600924 <i>
0x40055e <main+34>: movl $0x3,0x2003bc(%rip) # 0x600924 <i>
(gdb) PASS: gdb.base/consecutive-step-over.exp: get breakpoint addresses
break *0x40054a
Breakpoint 2 at 0x40054a: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 23.
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 1: set breakpoint
condition $bpnum condition
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 1: set condition
break *0x400554
Breakpoint 3 at 0x400554: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 24.
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 2: set breakpoint
condition $bpnum condition
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 2: set condition
break *0x40055e
Breakpoint 4 at 0x40055e: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 25.
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 3: set breakpoint
condition $bpnum condition
(gdb) PASS: gdb.base/consecutive-step-over.exp: insn 3: set condition
break 27
Breakpoint 5 at 0x400568: file ../../../src/gdb/testsuite/gdb.base/consecutive-step-over.c, line 27.
(gdb) continue
Continuing.
../../src/gdb/infrun.c:5200: internal-error: switch_back_to_stepped_thread: Assertion `!tp->control.trap_expected' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
FAIL: gdb.base/consecutive-step-over.exp: continue to breakpoint: break here (GDB internal error)
The assertion fails, because the code is not expecting that the event
thread itself might need another step over. IOW, not expecting that
TP in:
tp = find_thread_needs_step_over (stepping_thread != NULL,
stepping_thread);
could be the event thread.
A small fix for this would be to clear the event thread's
trap_expected earlier, before asserting. But looking deeper, although
currently_stepping_or_nexting_callback's intention is finding the
thread that is doing a step/next, it also returns the thread that is
doing a step-over dance, with trap_expected set. If there ever was a
reason for that (it was I who added
currently_stepping_or_nexting_callback , but I can't recall why I put
trap_expected there in the first place), the only remaining reason
nowadays is to aid in implementing switch_back_to_stepped_thread's
assertion that is now triggering, by piggybacking on the walk over all
threads, thus avoiding a separate walk. This is quite obscure, and I
think we can do even better, by merging the walks that look for the
stepping thread, and the walk that looks for some thread that might
need a step over.
Tested on x86_64 Fedora 17, native and gdbserver, and also native on
top of my "software single-step on x86_64" series.
gdb/
2014-04-22 Pedro Alves <palves@redhat.com>
* infrun.c (schedlock_applies): New function, factored out from
find_thread_needs_step_over.
(find_thread_needs_step_over): Use it.
(switch_back_to_stepped_thread): Always clear trap_expected if the
step over is finished. Return early if scheduler locking applies.
Look for the stepping thread and a potential step-over thread with
a single loop.
(currently_stepping_or_nexting_callback): Delete.
2014-04-22 Pedro Alves <palves@redhat.com>
* gdb.base/consecutive-step-over.c: New file.
* gdb.base/consecutive-step-over.exp: New file.
This commit is contained in:
Pedro Alves
parent
06d9754365
commit
483805cf9e
@ -1,3 +1,14 @@
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2014-04-22 Pedro Alves <palves@redhat.com>
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* infrun.c (schedlock_applies): New function, factored out from
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find_thread_needs_step_over.
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(find_thread_needs_step_over): Use it.
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(switch_back_to_stepped_thread): Always clear trap_expected if the
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step over is finished. Return early if scheduler locking applies.
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Look for the stepping thread and a potential step-over thread with
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a single loop.
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(currently_stepping_or_nexting_callback): Delete.
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2014-04-22 Nick Clifton <nickc@redhat.com>
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* NEWS: Mention that ARM sim now supports tracing.
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125
gdb/infrun.c
125
gdb/infrun.c
@ -85,9 +85,6 @@ static void set_schedlock_func (char *args, int from_tty,
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static int currently_stepping (struct thread_info *tp);
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static int currently_stepping_or_nexting_callback (struct thread_info *tp,
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void *data);
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static void xdb_handle_command (char *args, int from_tty);
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static void print_exited_reason (int exitstatus);
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@ -2107,6 +2104,17 @@ thread_still_needs_step_over (struct thread_info *tp)
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return 0;
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}
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/* Returns true if scheduler locking applies. STEP indicates whether
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we're about to do a step/next-like command to a thread. */
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static int
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schedlock_applies (int step)
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{
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return (scheduler_mode == schedlock_on
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|| (scheduler_mode == schedlock_step
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&& step));
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}
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/* Look a thread other than EXCEPT that has previously reported a
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breakpoint event, and thus needs a step-over in order to make
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progress. Returns NULL is none is found. STEP indicates whether
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@ -2116,21 +2124,16 @@ thread_still_needs_step_over (struct thread_info *tp)
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static struct thread_info *
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find_thread_needs_step_over (int step, struct thread_info *except)
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{
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int schedlock_enabled;
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struct thread_info *tp, *current;
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/* With non-stop mode on, threads are always handled individually. */
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gdb_assert (! non_stop);
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schedlock_enabled = (scheduler_mode == schedlock_on
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|| (scheduler_mode == schedlock_step
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&& step));
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current = inferior_thread ();
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/* If scheduler locking applies, we can avoid iterating over all
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threads. */
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if (schedlock_enabled)
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if (schedlock_applies (step))
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{
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if (except != current
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&& thread_still_needs_step_over (current))
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@ -5137,6 +5140,7 @@ switch_back_to_stepped_thread (struct execution_control_state *ecs)
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{
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struct thread_info *tp;
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struct thread_info *stepping_thread;
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struct thread_info *step_over;
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/* If any thread is blocked on some internal breakpoint, and we
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simply need to step over that breakpoint to get it going
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@ -5179,17 +5183,72 @@ switch_back_to_stepped_thread (struct execution_control_state *ecs)
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return 1;
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}
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stepping_thread
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= iterate_over_threads (currently_stepping_or_nexting_callback,
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ecs->event_thread);
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/* Otherwise, we no longer expect a trap in the current thread.
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Clear the trap_expected flag before switching back -- this is
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what keep_going does as well, if we call it. */
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ecs->event_thread->control.trap_expected = 0;
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/* Check if any other thread except the stepping thread that
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needs to start a step-over. Do that before actually
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proceeding with step/next/etc. */
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tp = find_thread_needs_step_over (stepping_thread != NULL,
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stepping_thread);
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if (tp != NULL)
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/* If scheduler locking applies even if not stepping, there's no
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need to walk over threads. Above we've checked whether the
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current thread is stepping. If some other thread not the
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event thread is stepping, then it must be that scheduler
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locking is not in effect. */
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if (schedlock_applies (0))
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return 0;
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/* Look for the stepping/nexting thread, and check if any other
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thread other than the stepping thread needs to start a
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step-over. Do all step-overs before actually proceeding with
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step/next/etc. */
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stepping_thread = NULL;
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step_over = NULL;
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ALL_THREADS (tp)
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{
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/* Ignore threads of processes we're not resuming. */
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if (!sched_multi
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&& ptid_get_pid (tp->ptid) != ptid_get_pid (inferior_ptid))
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continue;
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/* When stepping over a breakpoint, we lock all threads
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except the one that needs to move past the breakpoint.
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If a non-event thread has this set, the "incomplete
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step-over" check above should have caught it earlier. */
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gdb_assert (!tp->control.trap_expected);
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/* Did we find the stepping thread? */
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if (tp->control.step_range_end)
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{
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/* Yep. There should only one though. */
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gdb_assert (stepping_thread == NULL);
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/* The event thread is handled at the top, before we
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enter this loop. */
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gdb_assert (tp != ecs->event_thread);
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/* If some thread other than the event thread is
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stepping, then scheduler locking can't be in effect,
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otherwise we wouldn't have resumed the current event
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thread in the first place. */
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gdb_assert (!schedlock_applies (1));
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stepping_thread = tp;
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}
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else if (thread_still_needs_step_over (tp))
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{
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step_over = tp;
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/* At the top we've returned early if the event thread
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is stepping. If some other thread not the event
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thread is stepping, then scheduler locking can't be
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in effect, and we can resume this thread. No need to
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keep looking for the stepping thread then. */
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break;
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}
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}
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if (step_over != NULL)
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{
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tp = step_over;
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if (debug_infrun)
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{
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fprintf_unfiltered (gdb_stdlog,
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@ -5197,14 +5256,9 @@ switch_back_to_stepped_thread (struct execution_control_state *ecs)
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target_pid_to_str (tp->ptid));
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}
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gdb_assert (!tp->control.trap_expected);
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/* Only the stepping thread should have this set. */
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gdb_assert (tp->control.step_range_end == 0);
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/* We no longer expect a trap in the current thread. Clear
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the trap_expected flag before switching. This is what
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keep_going would do as well, if we called it. */
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ecs->event_thread->control.trap_expected = 0;
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ecs->ptid = tp->ptid;
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ecs->event_thread = tp;
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switch_to_thread (ecs->ptid);
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@ -5212,12 +5266,13 @@ switch_back_to_stepped_thread (struct execution_control_state *ecs)
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return 1;
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}
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tp = stepping_thread;
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if (tp != NULL)
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if (stepping_thread != NULL)
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{
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struct frame_info *frame;
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struct gdbarch *gdbarch;
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tp = stepping_thread;
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/* If the stepping thread exited, then don't try to switch
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back and resume it, which could fail in several different
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ways depending on the target. Instead, just keep going.
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@ -5250,11 +5305,6 @@ switch_back_to_stepped_thread (struct execution_control_state *ecs)
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return 1;
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}
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/* Otherwise, we no longer expect a trap in the current thread.
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Clear the trap_expected flag before switching back -- this is
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what keep_going would do as well, if we called it. */
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ecs->event_thread->control.trap_expected = 0;
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if (debug_infrun)
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fprintf_unfiltered (gdb_stdlog,
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"infrun: switching back to stepped thread\n");
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@ -5325,19 +5375,6 @@ currently_stepping (struct thread_info *tp)
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|| bpstat_should_step ());
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}
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/* Returns true if any thread *but* the one passed in "data" is in the
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middle of stepping or of handling a "next". */
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static int
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currently_stepping_or_nexting_callback (struct thread_info *tp, void *data)
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{
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if (tp == data)
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return 0;
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return (tp->control.step_range_end
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|| tp->control.trap_expected);
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}
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/* Inferior has stepped into a subroutine call with source code that
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we should not step over. Do step to the first line of code in
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it. */
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@ -1,3 +1,8 @@
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2014-04-22 Pedro Alves <palves@redhat.com>
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* gdb.base/consecutive-step-over.c: New file.
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* gdb.base/consecutive-step-over.exp: New file.
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2014-04-22 Pedro Alves <palves@redhat.com>
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* lib/gdb.exp (gdb_continue_to_breakpoint): Use gdb_test_multiple
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28
gdb/testsuite/gdb.base/consecutive-step-over.c
Normal file
28
gdb/testsuite/gdb.base/consecutive-step-over.c
Normal file
@ -0,0 +1,28 @@
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/* Copyright 2014 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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volatile int i;
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volatile int condition;
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int
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main (void)
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{
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i = 0;
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i = 1;
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i = 2;
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i = 3;
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return 0; /* break here */
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}
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70
gdb/testsuite/gdb.base/consecutive-step-over.exp
Normal file
70
gdb/testsuite/gdb.base/consecutive-step-over.exp
Normal file
@ -0,0 +1,70 @@
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# Copyright 2014 Free Software Foundation, Inc.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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#
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# Regression test for a bug where GDB would internal error if a thread
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# runs into a breakpoint that needs stepping over, just after stepping
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# over another breakpoint, without a user visible stop in between.
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#
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standard_testfile
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if {[prepare_for_testing "failed to prepare" $testfile $srcfile debug]} {
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return -1
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}
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if ![runto_main] then {
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fail "Can't run to main"
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return 0
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}
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# Make sure the target doesn't hide the breakpoint hits (that don't
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# cause a user visible stop) from GDB.
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gdb_test_no_output "set breakpoint condition-evaluation host"
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set up_to_nl "\[^\r\n\]+\[\r\n\]+"
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# Number of consecutive breakpoints in a row to try.
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set n_insns 3
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# Extract addresses of a few consecutive instructions.
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set test "get breakpoint addresses"
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if { [gdb_test_multiple "x /[expr $n_insns + 1]i \$pc" $test {
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-re "=> $hex${up_to_nl} ($hex)${up_to_nl} ($hex)${up_to_nl} ($hex)${up_to_nl}$gdb_prompt $" {
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for {set i 1} {$i <= $n_insns} {incr i} {
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set bp_addrs($i) $expect_out($i,string)
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}
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pass $test
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}
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}] != 0 } {
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# No use proceeding if bp_addrs wasn't set.
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return
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}
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for {set i 1} {$i <= $n_insns} {incr i} {
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with_test_prefix "insn $i" {
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gdb_test "break \*$bp_addrs($i)" \
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"Breakpoint $decimal at $bp_addrs($i): file .*" \
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"set breakpoint"
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# Give the breakpoint a condition that always fails, so that
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# the thread is immediately re-resumed.
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gdb_test_no_output "condition \$bpnum condition" \
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"set condition"
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}
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}
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set lineno [gdb_get_line_number "break here"]
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gdb_breakpoint $lineno
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gdb_continue_to_breakpoint "break here" ".*break here.*"
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Loading…
Reference in New Issue
Block a user