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.