From: Luis Machado <lgustavo@codesourcery.com>
To: Pedro Alves <palves@redhat.com>,
"'gdb-patches@sourceware.org'" <gdb-patches@sourceware.org>
Subject: Re: qemu-system debugging broken ([PATCH 03/18] remote.c/all-stop: Implement TARGET_WAITKIND_NO_RESUMED and TARGET_WNOHANG)
Date: Thu, 10 Sep 2015 11:38:00 -0000 [thread overview]
Message-ID: <55F16BB2.5000504@codesourcery.com> (raw)
In-Reply-To: <55F1595B.1050206@redhat.com>
Hi Pedro,
On 09/10/2015 07:20 AM, Pedro Alves wrote:
> Hi Luis,
>
> Sorry, I was away last week, and am still catching up.
>
No worries. I have since figured this out and addressed it in a
different message ...
> On 08/27/2015 11:19 PM, Luis Machado wrote:
>> Just a heads-up. It looks like this particular commit...
>>
>> commit 567420d10895611e03d5ee65e6b24c16a69a6e99
>> Author: Pedro Alves <palves@redhat.com>
>> Date: Fri Aug 7 17:23:56 2015 +0100
>>
>> remote.c/all-stop: Implement TARGET_WAITKIND_NO_RESUMED and
>> TARGET_WNOHANG
>>
>> Even though "target remote" supports target-async, the all-stop
>> target_wait implementation ignores TARGET_WNOHANG. If the core
>> happens to poll for events and we've already read the stop reply out
>> of the serial/socket, remote_wait_as hangs forever instead of
>> returning an indication that there are no events to process. This
>> can't happen currently, but later changes will trigger this.
>>
>> gdb/ChangeLog:
>> 2015-08-07 Pedro Alves <palves@redhat.com>
>>
>> * remote.c (remote_wait_as): If not waiting for a stop reply,
>> return TARGET_WAITKIND_NO_RESUMED. If TARGET_WNOHANG is
>> requested, don't block waiting forever.
>>
>> ... broke simulator-based debugging. The following is what i get when
>> trying to run the gdb.base/break binary on qemu-system for arm eabi:
>>
>> _ftext () at arm-vector.S:25
>> 25 ldr pc, [pc, #24] @ reset
>> (gdb) load
>> Loading section .text, size 0xc01c lma 0x0
>> Loading section .eh_frame, size 0x48 lma 0xc01c
>> Loading section .ARM.exidx, size 0x8 lma 0xc064
>> Loading section .rodata, size 0x398 lma 0xc070
>> Loading section .data, size 0x8e0 lma 0xc408
>> Start address 0x40, load size 52452
>> Transfer rate: 17074 KB/sec, 1748 bytes/write.
>> (gdb) c
>> Continuing.
>> infrun: clear_proceed_status_thread (Thread 1)
>> infrun: proceed (addr=0xffffffff, signal=GDB_SIGNAL_DEFAULT)
>> infrun: resume (step=0, signal=GDB_SIGNAL_0), trap_expected=0, current
>> thread [Thread 1] at 0x40
>> infrun: infrun_async(1)
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun: -1.0.0 [Thread 0],
>> infrun: status->kind = ignore
>> infrun: TARGET_WAITKIND_IGNORE
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun: -1.0.0 [Thread 0],
>> infrun: status->kind = ignore
>> infrun: TARGET_WAITKIND_IGNORE
>> infrun: prepare_to_wait
>> infrun: target_wait (-1.0.0, status) =
>> infrun: -1.0.0 [Thread 0],
>> infrun: status->kind = no-resumed
>> infrun: TARGET_WAITKIND_NO_RESUMED
>> infrun: stop_waiting
>> infrun: clear_step_over_info
>> No unwaited-for children left.
>> infrun: infrun_async(0)
>> (gdb) c
>> Continuing.
>> Cannot execute this command while the selected thread is running.
>> (gdb)
>> Continuing.
>> Cannot execute this command while the selected thread is running.
>>
>> Upon further inspection, it looks like the setting of status->kind to
>> TARGET_WAITKIND_NO_RESUMED in remote_wait_as causes GDB to stop waiting
>> for events and marks the active thread as running, returning the GDB
>> prompt and printing the old familiar message.
>>
>> Without setting TARGET_WAITKIND_NO_RESUMED, things worked fine and the
>> binary runs to completion, like so:
>
> ...
>
>> It sounds like we shouldn't drop to the prompt while we wait for
>> something to happen in all-stop mode either.
>
> Yes, but if the target was resumed, how come rs->waiting_for_stop_reply
> was false?
>
> if (!rs->waiting_for_stop_reply)
> {
> status->kind = TARGET_WAITKIND_NO_RESUMED;
> return minus_one_ptid;
> }
>
> I suspect that what happens is that qemu sends an F packet, and
> we miss setting waiting_for_stop_reply true back, like we do
> in the other cases:
>
> gdb/remote:remote_wait_as ()
> {
> ...
> /* We got something. */
> rs->waiting_for_stop_reply = 0;
> ...
> case 'F': /* File-I/O request. */
> remote_fileio_request (buf, rs->ctrlc_pending_p);
> rs->ctrlc_pending_p = 0;
> break;
> ...
>
> Looks like it'd be simpler to instead only clear
> waiting_for_stop_reply in the stop reply cases, instead of
> re-setting it in some cases, forgetting others.
... and it is really the case that we were forgetting to reset
rs->ctrlc_pending_p.
prev parent reply other threads:[~2015-09-10 11:38 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-27 22:19 Luis Machado
2015-09-10 10:20 ` Pedro Alves
2015-09-10 11:38 ` Luis Machado [this message]
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