Re: sim_engine_halt() broken in binutils 2.34

On Sun, Feb 2, 2020 at 4:47 PM Andrew Burgess
<[email protected]> wrote:
>
> * William Tambe <[email protected]> [2020-02-02 00:03:40 -0500]:
>
> > I am running GDB with target sim.
> >
> > Calling sim_engine_halt() triggers the following error:
> > ../../binutils-gdb/gdb/inferior.c:286: internal-error: inferior*
> > find_inferior_pid(process_stratum_target*, int): Assertion `pid != 0'
> > failed.
> > A problem internal to GDB has been detected,
> > further debugging may prove unreliable.
> > Quit this debugging session? (y or n)
> >
> > Any idea idea what changed ?
>
> I suspect that this is a similar issue (but not the exact same fix) as
> something I already posted here:
>
>    https://sourceware.org/ml/gdb-patches/2020-01/msg00980.html

I tried using above fix, but it did not resolve the issue.

>
> You could double check if you like, I believe if you check out the
> commit just before 5b6d1e4fa4fc682 then you'll find your issue goes
> away.

I could not quickly test above as I need to do rebase adjustments for
the custom port that I am using.

>
> The problem is caused, I suspect, by a use of `inferior_ptid' at a
> place where this used to not be the null_ptid, but now is null_ptid.
>
> I had a little nose around for places related to the simulator where
> this bug might be hiding, but couldn't see anything obvious.
>
> If you could let us know which simulator you're using, and what you do
> to trigger the call to sim_engine_halt then we might be able to
> reproduce the issue.

The simulator I am using is a custom port that is not upstream.

sim_engine_halt() is used by simulators to do things like SIM_SIGTRAP,
SIGABRT, SIGILL or SIM_SIGSEGV;
The fact that sim_engine_halt() is broken makes gdb target sim useless
because breakpoints cannot be set.

>
> You could also try to collect a backtrace from GDB at the point the
> assertion triggers, I believe GDB offers to dump core on an assertion,
> so you can use that to obtain the backtrace.  We might get lucky, and
> something in the backtrace could be the offender.

See below backtrace from GDB when assert triggers due to
sim_engine_halt() getting called for a breakpoint using SIM_SIGTRAP:

../../binutils-gdb/gdb/inferior.c:279: internal-error: inferior*
find_inferior_pid(process_stratum_target*, int): Assertion `pid != 0'
failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)
(gdb) bt
#0  0x00007ffff66c9bf9 in __GI___poll (fds=0x555555fd36e0, nfds=4,
timeout=timeout@entry=-1) at ../sysdeps/unix/sysv/linux/poll.c:29
#1  0x00005555556ecf90 in poll (__timeout=-1, __nfds=<optimized out>,
__fds=<optimized out>) at
/usr/include/x86_64-linux-gnu/bits/poll2.h:46
#2  gdb_wait_for_event (block=block@entry=1) at
../../binutils-gdb/gdb/event-loop.c:769
#3  0x00005555556ed152 in gdb_do_one_event () at
../../binutils-gdb/gdb/event-loop.c:346
#4  0x00005555556ed286 in gdb_do_one_event () at
../../binutils-gdb/gdb/event-loop.c:352
#5  0x000055555585d60f in gdb_readline_wrapper (prompt=<optimized
out>) at ../../binutils-gdb/gdb/top.c:1078
#6  0x000055555588db16 in defaulted_query(const char *, char, typedef
__va_list_tag __va_list_tag *) (ctlstr=<optimized out>,
defchar=defchar@entry=0 '\000', args=args@entry=0x7fffffffd740)
    at ../../binutils-gdb/gdb/utils.c:867
#7  0x000055555588de5b in query (ctlstr=<optimized out>) at
../../binutils-gdb/gdb/utils.c:959
#8  0x000055555588e3a6 in internal_vproblem(internal_problem *, const
char *, int, const char *, typedef __va_list_tag __va_list_tag *) (
    problem=problem@entry=0x555555d59880 <internal_error_problem>,
file=<optimized out>, line=279, fmt=<optimized out>,
ap=ap@entry=0x7fffffffd900) at ../../binutils-gdb/gdb/utils.c:372
#9  0x000055555588e4eb in internal_verror (file=<optimized out>,
line=<optimized out>, fmt=<optimized out>, ap=ap@entry=0x7fffffffd900)
at ../../binutils-gdb/gdb/utils.c:438
#10 0x00005555559590df in internal_error
(file=file@entry=0x5555559f2cd0 "../../binutils-gdb/gdb/inferior.c",
line=line@entry=279, fmt=<optimized out>)
    at ../../binutils-gdb/gdbsupport/errors.c:55
#11 0x000055555572e72f in find_inferior_pid (targ=<optimized out>,
pid=<optimized out>) at ../../binutils-gdb/gdb/inferior.c:279
#12 0x0000555555856905 in find_thread_ptid
(targ=targ@entry=0x555555d58f60 <gdbsim_ops>, ptid=...) at
../../binutils-gdb/gdb/thread.c:527
#13 0x000055555573f42d in handle_inferior_event
(ecs=ecs@entry=0x7fffffffdd30) at ../../binutils-gdb/gdb/infrun.c:5062
#14 0x000055555574096f in fetch_inferior_event (client_data=<optimized
out>) at ../../binutils-gdb/gdb/infrun.c:4002
#15 0x00005555556ed19c in check_async_event_handlers () at
../../binutils-gdb/gdb/event-loop.c:1062
#16 gdb_do_one_event () at ../../binutils-gdb/gdb/event-loop.c:325
#17 0x00005555556ed2be in gdb_do_one_event () at
../../binutils-gdb/gdb/event-loop.c:303
#18 start_event_loop () at ../../binutils-gdb/gdb/event-loop.c:370
#19 0x0000555555765018 in captured_command_loop () at
../../binutils-gdb/gdb/main.c:360
#20 0x0000555555766f75 in captured_main (data=<optimized out>) at
../../binutils-gdb/gdb/main.c:1203
#21 gdb_main (args=<optimized out>) at ../../binutils-gdb/gdb/main.c:1218
#22 0x00005555555bff1b in main (argc=<optimized out>, argv=<optimized
out>) at ../../binutils-gdb/gdb/gdb.c:32

>
> Best of luck!
>
> Andrew
>