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

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

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

            Bug ID: 19736
           Summary: GDBserver gets internal error when the thread which is
                    stepping over breakpoint fork/vfork/clone new thread
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: server
          Assignee: unassigned at sourceware dot org
          Reporter: qiyao at gcc dot gnu.org
  Target Milestone: ---

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

This GDBserver internal error can be reproduced by
gdb.base/step-over-syscall.exp.

FAIL: gdb.base/step-over-syscall.exp: break cond on target : fork: continue to
marker (fork)
FAIL: gdb.base/step-over-syscall.exp: break cond on target : vfork: continue to
marker (vfork)
FAIL: gdb.base/step-over-syscall.exp: break cond on target : clone: continue to
marker (clone)

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