[Bug gdb/18749] New: problems if whole process dies while (ptrace-) stopped

[Bug gdb/18749] New: problems if whole process dies while (ptrace-) stopped

[palves at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18749

            Bug ID: 18749
           Summary: problems if whole process dies while (ptrace-) stopped
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: palves at redhat dot com
  Target Milestone: ---

Between fetching a thread stop event (on Linux, after waitpid returns a stop)
and fully handling the event (e.g., all the way evaluating a breakpoint
condition and reresuming if it evals false), some other thread that is still
running may cause the whole process to exit.  Usually in such a situation, the
lower level code that tries to access memory or registers throws an error
(usually a perror_with_name/ESRCH), and many code paths in GDB don't expect
this, resulting in a broken debug session.

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[Bug gdb/18749] problems if whole process dies while (ptrace-) stopped

[palves at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18749

--- Comment #1 from Pedro Alves <palves at redhat dot com> ---
I'm adding a test to the testsuite that exposes several of these on at least
native GNU/Linux:

E.g., on one run:

 [Thread 0x7ffff6fbe700 (LWP 1332) exited]
 Cannot access memory at address 0x400872

And on another:
 [Thread 0x7ffff3fb8700 (LWP 2161) exited]
 Cannot find user-level thread for LWP 2163: generic error
 (gdb) [Thread 0x7ffff2fb6700 (LWP 2163) exited]
 [Thread 0x7ffff47b9700 (LWP 2160) exited]

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[Bug gdb/18749] problems if whole process dies while (ptrace-) stopped

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18749

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Pedro Alves <palves@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=465a859e0a991d3bfe8a9ee65a29a223c42e2ce7

commit 465a859e0a991d3bfe8a9ee65a29a223c42e2ce7
Author: Pedro Alves <palves@redhat.com>
Date:   Fri Aug 21 19:52:36 2015 +0100

    Fix gdbserver crash exposed by
gdb.threads/process-dies-while-handling-bp.exp

    Running that test in a loop, I found a gdbserver core dump with the
    following back trace:

     Core was generated by `../gdbserver/gdbserver --once --multi :2346'.
     Program terminated with signal SIGSEGV, Segmentation fault.
     #0  0x0000000000406ab6 in inferior_regcache_data (inferior=0x0) at
src/gdb/gdbserver/inferiors.c:236
     236       return inferior->regcache_data;
     (gdb) up
     #1  0x0000000000406d7f in get_thread_regcache (thread=0x0, fetch=1) at
src/gdb/gdbserver/regcache.c:31
     31        regcache = (struct regcache *) inferior_regcache_data (thread);
     (gdb) bt
     #0  0x0000000000406ab6 in inferior_regcache_data (inferior=0x0) at
src/gdb/gdbserver/inferiors.c:236
     #1  0x0000000000406d7f in get_thread_regcache (thread=0x0, fetch=1) at
src/gdb/gdbserver/regcache.c:31
     #2  0x0000000000409271 in prepare_resume_reply (buf=0x20dd593 "",
ptid=..., status=0x20edce0) at src/gdb/gdbserver/remote-utils.c:1147
     #3  0x000000000040ab0a in vstop_notif_reply (event=0x20edcc0,
own_buf=0x20dd590 "T05") at src/gdb/gdbserver/server.c:183
     #4  0x0000000000426b38 in notif_write_event (notif=0x66e6c0 <notif_stop>,
own_buf=0x20dd590 "T05") at src/gdb/gdbserver/notif.c:69
     #5  0x0000000000426c55 in handle_notif_ack (own_buf=0x20dd590 "T05",
packet_len=8) at src/gdb/gdbserver/notif.c:113
     #6  0x000000000041118f in handle_v_requests (own_buf=0x20dd590 "T05",
packet_len=8, new_packet_len=0x7fff742c77b8)
         at src/gdb/gdbserver/server.c:2862
     #7  0x0000000000413850 in process_serial_event () at
src/gdb/gdbserver/server.c:4148
     #8  0x0000000000413945 in handle_serial_event (err=0, client_data=0x0) at
src/gdb/gdbserver/server.c:4196
     #9  0x000000000041a1ef in handle_file_event (event_file_desc=5) at
src/gdb/gdbserver/event-loop.c:429
     #10 0x00000000004199b6 in process_event () at
src/gdb/gdbserver/event-loop.c:184
     #11 0x000000000041a735 in start_event_loop () at
src/gdb/gdbserver/event-loop.c:547
     #12 0x00000000004123d2 in captured_main (argc=4, argv=0x7fff742c7ac8) at
src/gdb/gdbserver/server.c:3562
     #13 0x000000000041252e in main (argc=4, argv=0x7fff742c7ac8) at
src/gdb/gdbserver/server.c:3631

    Clearly this means that a thread pushed a stop reply in the event
    queue, and then before GDB confused the event, the whole process died,
    along with its thread.  But the pending thread event was left
    dangling.  When GDB fetched that event, gdbserver looked up the
    corresponding thread, but found NULL; not expecting this, gdbserver
    crashes when it tries to read this thread's registers.

    gdb/gdbserver/
    2015-08-21  Pedro Alves  <palves@redhat.com>

        PR gdb/18749
        * inferiors.c (remove_thread): Discard any pending stop reply for
        this thread.
        * server.c (remove_all_on_match_pid): Rename to ...
        (remove_all_on_match_ptid): ... this.  Work with a filter ptid
        instead of a pid.
        (discard_queued_stop_replies): Change parameter to a ptid.  Now
        extern.
        (handle_v_kill, kill_inferior_callback)
        (process_serial_event): Adjust.
        (captured_main): Call initialize_notif before starting the
        program, thus before threads are created.
        * server.h (discard_queued_stop_replies): Declare.

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[Bug gdb/18749] problems if whole process dies while (ptrace-) stopped

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18749

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ssbssa at sourceware dot org

--- Comment #5 from Hannes Domani <ssbssa at sourceware dot org> ---
(In reply to Sourceware Commits from comment #4)
> The master branch has been updated by Yao Qi <qiyao@sourceware.org>:
> 
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;
> h=9a70f35c8d872bb5542e98e34b8b044228dcb844
> 
> commit 9a70f35c8d872bb5542e98e34b8b044228dcb844
> Author: Yao Qi <yao.qi@linaro.org>
> Date:   Tue Jan 16 09:05:39 2018 +0000
> 
>     Mark register unavailable when PTRACE_PEEKUSER fails
>     
>     As described in PR 18749, GDB/GDBserver may get an error on accessing
>     memory or register because the thread may disappear.  However, some
>     path doesn't expect the error.  This patch fixes this problem by
>     marking the register unavailable when PTRACE_PEEKUSER fails instead
>     of throwing error.
>     
>     gdb/gdbserver:
>     
>     2018-01-16  Yao Qi  <yao.qi@linaro.org>
>     
>     	PR gdb/18749
>     	* linux-low.c (fetch_register): Call supply_register instead of
>     	error.

Can this be closed?

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