[Bug server/20053] New: As a side effect of patch supporting "Target remote mode fork and exec event support". Cross-debugging with gdbserver fails to hit breakpoint in parent after many fork / exec's.

["ranjan.amit8 at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=20053

            Bug ID: 20053
           Summary: As a side effect of patch supporting "Target remote
                    mode fork and exec event support". Cross-debugging
                    with gdbserver fails to hit breakpoint in parent after
                    many fork / exec's.
           Product: gdb
           Version: 7.11
            Status: NEW
          Severity: critical
          Priority: P2
         Component: server
          Assignee: unassigned at sourceware dot org
          Reporter: ranjan.amit8 at gmail dot com
  Target Milestone: ---

On my target(x86_64) after cross-debugging a program with "follow fork / follow
exec" enabled, it fails to hit a breakpoint in the parent program after many
fork/exec's. The gdbserver prints following error message near the end of the
program: 

  gdb/7.11-r0/gdb-7.11/gdb/gdbserver/linux-low.c:1922: A problem internal to
GDBserver has been detected. 
unsuspend LWP 842, suspended=-1 

And Host Side I am getting gdb error as:

gdb-cross-x86_64/7.11-r0/gdb-7.11/gdb/thread.c:1100: internal-error:
finish_thread_state: Assertion `tp' failed. 
A problem internal to GDB has been detected, 
further debugging may prove unreliable. 
-----------------

STEPS TO REPRODUCE:-

wget http://www.gzip.org/gz124src.zip 
unzip gz124src.zip 
cd gz124 
./configure 
time make -j 4 # real 1.5 sec / user 5.124 sec 
make clean 
gdbserver :1234 time make -j 4 

# Back on the host, perform the following: 
gdb 
set non-stop on 
target remote 128.224.199.101:1234 
set pagination off 
set follow-fork-mode parent 
set detach-on-fork off 
b time.c:654 
cont 

--> The program runs to end, and gdbserver prints an error 
--> Expected: The breakpoint at time.c:654 should hit.
-------------

ANALYSIS:-

On Analyzing the issue I identified that patch supporting the functionality
"support fork and exec events for target remote mode Linux targets",
reference:(https://sourceware.org/ml/gdb-patches/2015-11/msg00209.html)
is causing the problem. If we remove this particular patch then issue gets
resolved. May be this patch have some side effect which is not taken care.
Up-streamed Link:-
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=8020350c5277e056e89b0ea5e14a8d09408f7fb3
--------------------

References:- https://sourceware.org/bugzilla/show_bug.cgi?id=13584

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