[06/16,v3] Extended-remote Linux follow fork

  This patch implements basic support for follow-fork and detach-on-fork on
extended-remote Linux targets.  Only 'fork' is supported in this patch;
'vfork' support is added n a subsequent patch.  Sufficient extended-remote
functionality has been implemented here to pass gdb.base/foll-fork.exp with
the catchpoint tests commented out.

The implementation follows the same general structure as for the native
implementation as much as possible.

This implementation included:
 * enabling fork events in linux-low.c in initialize_low and
   linux_enable_extended_features

   - this adds the ptrace option to trace fork events to the new functions
     from patch 4 that set up ptrace options.

 * handling fork events in gdbserver/linux-low.c:handle_extended_wait

   - when a fork event occurs in gdbserver, we must do the full creation
     of the new process, thread, lwp, and breakpoint lists.  This is
     required whether or not the new child is destined to be
     detached-on-fork, because GDB will make target calls that require all
     the structures.  In particular we need the breakpoint lists in order
     to remove the breakpoints from a detaching child.  If we are not
     detaching the child we will need all these structures anyway.

   - as part of this event handling we store the target_waitstatus in a new
     member of the parent thread_info structure, 'pending_follow'.  This
     mimics a similar mechanism used in the native implementation.  Here is
     it used in several ways:
     - in remote_detach_1 to distinguish between a process that is being
       detached-on-fork vs. just detached.  In the fork case we don't want
       to mourn the process because we want to keep the inferior around in
       case the user decides to run the inferior again.
     - to record the child pid for the expected follow_fork request.
     - to find the parent in follow_fork (and later, elsewhere).

   - we also store the waitstatus in a new lwp_info member, 'waitstatus',
     which is used in controlling the reporting of the event in
     linux_wait_1.  We cannot re-use pending_follow for this because we
     need to mark this one with 'ignored' status as part of the
     linux_wait_1 procedure to stop event processing, and we need to keep
     pending_follow intact for use later on.  We will also need this later
     on for exec event handling, where pending_follow makes no sense.

   - handle_extended_wait is given a return value, denoting whether the
     handled event should be reported to GDB.  Previously it had only
     handled clone events, which were never reported.

 * using a new predicate to control handling of the fork event (and 
   eventually all extended events) in linux_wait_1.  The predicate,
   extended_event_reported, checks a target_waitstatus.kind for an
   extended ptrace event.

 * implementing a new RSP 'T' Stop Reply Packet stop reason: "fork", in
   gdbserver/remote-utils.c and remote.c.

 * implementing new target and RSP support for target_follow_fork with
   target extended-remote.  (The RSP components were actually defined in
   patch 4, but they see their first use here).

   - extended_remote target routine extended_remote_follow_fork

   - RSP packet vFollowFork

   - in gdbserver struct target_ops, add functions linux_supports_follow_fork
     and linux_follow_fork.  The linux_follow_fork routine mimics the
     implementation of linux-nat.c:linux_child_follow_fork, but the data
     structures in use prevented turning this into a common function for now.

Tested on x64 Ubuntu Lucid, native, remote, extended-remote.

Thanks
--Don

gdb/gdbserver/
2014-10-31  Don Breazeal  <donb@codesourcery.com>

	* gdbthread.h (struct thread_info) <pending_follow>: New member.
	* linux-low.c (handle_extended_wait): Change function type from
	void to int, handle PTRACE_EVENT_FORK, call internal_error.
	(is_parent_callback): New function.
	(linux_follow_fork): New function.
	(linux_low_filter_event): Handle return value from
	handle_extended_wait.
	(extended_event_reported): New function.
	(linux_write_memory): Add pid to debug print.
	(linux_target_ops) <follow_fork>: Initialize new member.
	(initialize_low): Add PTRACE_O_TRACEFORK option.
	* linux-low.h (struct lwp_info) <waitstatus>: New member.
	* lynx-low.c (lynx_target_ops) <follow_fork>: Initialize new member.
	* remote-utils.c (prepare_resume_reply): New RSP stop reason "fork"
	for 'T' stop reply.
	* server.c (handle_v_follow_fork): New function.
	(handle_v_requests): Handle vFollowFork packet, call
	handle_v_follow_fork.
	* target.h (struct target_ops) <follow_fork>: New member.
	(target_follow_fork): Define macro.
	* win32-low.c (win32_target_ops) <follow_fork>: Initialize new member.

gdb/
2014-10-31  Don Breazeal  <donb@codesourcery.com>

	* gdb/nat/linux-ptrace.c (current_ptrace_options): Update comment.
	* remote.c (extended_remote_follow_fork): Implement follow-fork.
	(remote_detach_1): Add target_ops argument, handle detach-on-fork.
	(remote_detach, extended_remote_detach): Call remote_detach_1
	with target_ops argument.
	(remote_parse_stop_reply): Handle new RSP stop reason "fork" in
	'T' stop reply packet.
	(remote_pid_to_str): Print process.
	(_initialize_remote): Call add_packet_config_cmd for new RSP packet.

---
 gdb/gdbserver/gdbthread.h    |    5 +
 gdb/gdbserver/linux-low.c    |  207 +++++++++++++++++++++++++++++++++++++++---
 gdb/gdbserver/linux-low.h    |    5 +
 gdb/gdbserver/lynx-low.c     |    1 +
 gdb/gdbserver/remote-utils.c |   14 +++-
 gdb/gdbserver/server.c       |   41 ++++++++
 gdb/gdbserver/target.h       |   13 +++
 gdb/gdbserver/win32-low.c    |    1 +
 gdb/nat/linux-ptrace.c       |    4 +-
 gdb/remote.c                 |   53 +++++++++--
 10 files changed, 319 insertions(+), 25 deletions(-)

[06/16,v3] Extended-remote Linux follow fork

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