follow-exec: delete all non-execing threads

This fixes invalid reads Valgrind first caught when debugging against
a GDBserver patched with a series that adds exec events to the remote
protocol.  Like these, using the gdb.threads/thread-execl.exp test:

$ valgrind ./gdb -data-directory=data-directory ./testsuite/gdb.threads/thread-execl  -ex "tar extended-remote :9999" -ex "b thread_execler" -ex "c" -ex "set scheduler-locking on"
...
Breakpoint 1, thread_execler (arg=0x0) at src/gdb/testsuite/gdb.threads/thread-execl.c:29
29        if (execl (image, image, NULL) == -1)
(gdb) n
Thread 32509.32509 is executing new program: build/gdb/testsuite/gdb.threads/thread-execl
[New Thread 32509.32532]
==32510== Invalid read of size 4
==32510==    at 0x5AA7D8: delete_breakpoint (breakpoint.c:13989)
==32510==    by 0x6285D3: delete_thread_breakpoint (thread.c:100)
==32510==    by 0x628603: delete_step_resume_breakpoint (thread.c:109)
==32510==    by 0x61622B: delete_thread_infrun_breakpoints (infrun.c:2928)
==32510==    by 0x6162EF: for_each_just_stopped_thread (infrun.c:2958)
==32510==    by 0x616311: delete_just_stopped_threads_infrun_breakpoints (infrun.c:2969)
==32510==    by 0x616C96: fetch_inferior_event (infrun.c:3267)
==32510==    by 0x63A2DE: inferior_event_handler (inf-loop.c:57)
==32510==    by 0x4E0E56: remote_async_serial_handler (remote.c:11877)
==32510==    by 0x4AF620: run_async_handler_and_reschedule (ser-base.c:137)
==32510==    by 0x4AF6F0: fd_event (ser-base.c:182)
==32510==    by 0x63806D: handle_file_event (event-loop.c:762)
==32510==  Address 0xcf333e0 is 16 bytes inside a block of size 200 free'd
==32510==    at 0x4A07577: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==32510==    by 0x77CB74: xfree (common-utils.c:98)
==32510==    by 0x5AA954: delete_breakpoint (breakpoint.c:14056)
==32510==    by 0x5988BD: update_breakpoints_after_exec (breakpoint.c:3765)
==32510==    by 0x61360F: follow_exec (infrun.c:1091)
==32510==    by 0x6186FA: handle_inferior_event (infrun.c:4061)
==32510==    by 0x616C55: fetch_inferior_event (infrun.c:3261)
==32510==    by 0x63A2DE: inferior_event_handler (inf-loop.c:57)
==32510==    by 0x4E0E56: remote_async_serial_handler (remote.c:11877)
==32510==    by 0x4AF620: run_async_handler_and_reschedule (ser-base.c:137)
==32510==    by 0x4AF6F0: fd_event (ser-base.c:182)
==32510==    by 0x63806D: handle_file_event (event-loop.c:762)
==32510==
[Switching to Thread 32509.32532]

Breakpoint 1, thread_execler (arg=0x0) at src/gdb/testsuite/gdb.threads/thread-execl.c:29
29        if (execl (image, image, NULL) == -1)
(gdb)

The breakpoint in question is the step-resume breakpoint of the
non-main thread, the one that was "next"ed.

The exact same issue can be seen on mainline with native debugging, by
running the thread-execl.exp test in non-stop mode, because the kernel
doesn't report a thread exit event for the execing thread.

Tested on x86_64 Fedora 20.

gdb/ChangeLog:
2015-03-02  Pedro Alves  <palves@redhat.com>

	* infrun.c (follow_exec): Delete all threads of the process except
	the event thread.  Extended comments.

gdb/testsuite/ChangeLog:
2015-03-02  Pedro Alves  <palves@redhat.com>

	* gdb.threads/thread-execl.exp (do_test): Handle non-stop.
	(top level): Call do_test with non-stop as well.

0 files changed, 0 insertions, 0 deletions