[Bug server/19736] GDBserver gets internal error when the thread which is stepping over breakpoint fork/vfork/clone new thread

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19736

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Yao Qi <qiyao@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=0f8288ae82bf5bdb33d46d7447cd3132393a1bd2

commit 0f8288ae82bf5bdb33d46d7447cd3132393a1bd2
Author: Yao Qi <yao.qi@linaro.org>
Date:   Thu Mar 3 09:17:44 2016 +0000

    [GDBserver] Leave child suspended when step over parent

    I see the following GDBserver internal error in two cases,

     gdb/gdbserver/linux-low.c:1922: A problem internal to GDBserver has been
detected.
     unsuspend LWP 17200, suspended=-1

     1. step over a breakpoint on fork/vfork syscall instruction,
     2. step over a breakpoint on clone syscall instruction and child
        threads hits a breakpoint,

    the stack backtrace is

     #0  internal_error (file=file@entry=0x44c4c0 "gdb/gdbserver/linux-low.c",
line=line@entry=1922,
        fmt=fmt@entry=0x44c7d0 "unsuspend LWP %ld, suspended=%d\n") at
gdb/gdbserver/../common/errors.c:51
     #1  0x0000000000424014 in lwp_suspended_decr (lwp=<optimised out>,
lwp=<optimised out>) at gdb/gdbserver/linux-low.c:1922
     #2  0x000000000042403a in unsuspend_one_lwp (entry=<optimised out>,
except=0x66e8c0) at gdb/gdbserver/linux-low.c:2885
     #3  0x0000000000405f45 in find_inferior (list=<optimised out>,
func=func@entry=0x424020 <unsuspend_one_lwp>, arg=arg@entry=0x66e8c0)
        at gdb/gdbserver/inferiors.c:243
     #4  0x00000000004297de in unsuspend_all_lwps (except=0x66e8c0) at
gdb/gdbserver/linux-low.c:2895
     #5  linux_wait_1 (ptid=..., ourstatus=ourstatus@entry=0x665ec0
<last_status>, target_options=target_options@entry=0)
        at gdb/gdbserver/linux-low.c:3632
     #6  0x000000000042a764 in linux_wait (ptid=..., ourstatus=0x665ec0
<last_status>, target_options=0)
        at gdb/gdbserver/linux-low.c:3770
     #7  0x0000000000411163 in mywait (ptid=...,
ourstatus=ourstatus@entry=0x665ec0 <last_status>, options=options@entry=0,
connected_wait=connected_wait@entry=1)
        at gdb/gdbserver/target.c:214
     #8  0x000000000040b1f2 in resume (actions=0x66f800, num_actions=1) at
gdb/gdbserver/server.c:2757
     #9  0x000000000040f660 in handle_v_cont (own_buf=0x66a630
"vCont;c:p45e9.-1") at gdb/gdbserver/server.c:2719

    when GDBserver steps over a thread, other threads have been suspended,
    the "stepping" thread may create new thread, but GDBserver doesn't set
    it suspend count to 1.  When GDBserver unsuspend threads, the child's
    suspend count goes to -1, and the assert is triggered.  In fact, GDBserver
    has already taken care of suspend count of new thread when GDBserver is
    suspending all threads except the one GDBserver wants to step over by
    https://sourceware.org/ml/gdb-patches/2015-07/msg00946.html

    +     /* If we're suspending all threads, leave this one suspended
    +        too.  */
    +     if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS)
    +       {
    +         if (debug_threads)
    +           debug_printf ("HEW: leaving child suspended\n");
    +         child_lwp->suspended = 1;
    +       }

    but that is not enough, because new thread is still can be spawned in
    the thread which is being stepped over.  This patch extends the
    condition that GDBserver set child's suspend count to one if it is
    suspending threads or stepping over the thread.

    gdb/gdbserver:

    2016-03-03  Yao Qi  <yao.qi@linaro.org>

        PR server/19736
        * linux-low.c (handle_extended_wait): Set child suspended
        if event_lwp->bp_reinsert isn't zero.

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