diff mbox

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

Message ID 1421102362-8902-1-git-send-email-donb@codesourcery.com
State New
Headers show

Commit Message

Don Breazeal Jan. 12, 2015, 10:39 p.m. UTC
Pedro Alves wrote:
> Let's try to shake out the higher-level concepts first before
> focusing on specific details.
---snip---
>>
>>  * 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
>
> Reading through this, I don't think this is the model we should be exposing
> at the RSP level, and requiring servers to support.  The hiding of the
> child fork until the users resumes is a current detail that we may want to
> change in the future.  It seems better to me to _not_ hide the child from
> GDB, and then implement the hide-child-until-resume detail in GDB.  That is,
> I think we should model fork events at the RSP level similarly to
> how ptrace and ttrace expose them.  So, e.g., I think switching to the
> child to write to its memory should be done with the regular Hg packet.
> Handling detach_fork would be done by GDB calling the regular
> detach packet (D;PID), etc.

I have updated the patch to eliminate the vFollowFork packet and to handle
detach_fork using a regular detach packet as you describe above.

>> My initial approach was to do just that, but I ended up with
>> linux-specific code in remote.c (the code that lives in linux-nat.c
>> for the native implementation).  I guess the direction of recent
>> changes would be to put that code into a common file in gdb/nat,
>> if possible.  Would that be the approach you would recommend?
>
> I'm not seeing what would be linux-specific?  On remote_follow_fork
> fork, we switch the current remote thread to gdb's current
> thread (either parent or child), by
> calling 'set_general_thread (inferior_ptid);'
> And then if we need to detach parent or child, we detach it with
> the D;PID packet.

There are two linux-specific issues, both of which are workarounds for
kernel issues.

1) workaround for the hardware single-step kernel bug that causes the 
   hardware single-step flag to be inherited across a vfork.  In
   linux-nat.c:linux_child_follow_fork we manually step the inferior
   before detaching.

2) workaround for kernels that support PTRACE_O_TRACEVFORK but not
   PTRACE_O_TRACEVFORKDONE.  In linux-nat.c:linux_child_follow_fork
   we run the vfork child for a little while, then create a fake
   vfork-done event.

I propose that we don't do either of these workarounds for remote 
follow fork.  For (1), the kernel fix that eliminates the need for
this looks like it is from 2009.  For (2), the workaround is for
kernels between versions 2.5.46 (04.Nov.2002) and 2.6.18 (20.Sep.2006).
Is it necessary to provide workarounds in a new feature for kernels
as old as these?  (1) in particular is difficult to implement, since
gdbserver has no way to know whether detach-on-fork has been set, or
whether a given detach has anything to do with a vfork that preceded
it.  OK to drop these?

> I'm not even seeing a fundamental need
> to keep this for "extended-remote" alone, given gdb nowadays supports
> the multiprocess extensions with "target remote" too.

I agree that we should do this.  As I described in the update to patch 04
(https://sourceware.org/ml/gdb-patches/2015-01/msg00320.html), I ran into
several issues with implementing follow-fork for target remote.  I think
the underlying target remote support, eliminating "gdbserver exit when
inferior terminates", deserves its own patch, and I'd like to defer that in
favor of making progress on the extended-remote piece.

Updated patch and commit message below.
Thanks!
--Don

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.  This patch depends on 
patches 04 and 05 of the patch series.

Sufficient extended-remote functionality has been implemented here to pass
gdb.base/multi-forks.exp and gdb.base/foll-fork.exp with the catchpoint
tests commented out.  Some other fork tests fail with this patch because it
doesn't provide the architecture support needed for watchpoint inheritance
or fork catchpoints.

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

 * 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
     is used to store extended event information for reporting to GDB.

   - 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 in gdbserver 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).

   - remote target routine remote_follow_fork, which just sends the 'D;pid'
     detach packet to detach the new fork child cleanly.  We can't just
     call target_detach because the fork child data structures have not
     been allocated on the host side.

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

gdb/gdbserver/
2015-01-12  Don Breazeal  <donb@codesourcery.com>

	* gdbthread.h (struct thread_info) <pending_follow>: New member.
	* linux-low.c (handle_extended_wait): Implement return value,
	handle PTRACE_EVENT_FORK.
	(linux_low_enable_events): New function.
	(linux_low_filter_event): Use return value from
	handle_extended_wait.
	(extended_event_reported): New function.
	(linux_write_memory): Add pid to debug message.
	(initialize_low): Pass PTRACE_O_TRACEFORK to set_additional_flags.
	* remote-utils.c (prepare_resume_reply): Implement stop reason
	"fork" for "T" stop message.
	* server.h (report_fork_events): Declare global flag.

gdb/
2015-01-12  Don Breazeal  <donb@codesourcery.com>

	* nat/linux-ptrace.c (linux_ptrace_clear_additional_flags): New
	function.
	* nat/linux-ptrace.h: (linux_ptrace_clear_additional_flags):
	Declare new function.
	* remote.c (remote_follow_fork): New function.
	(remote_detach_1): Add target_ops argument, don't mourn inferior
	if doing detach-on-fork.
	(remote_detach): Add target_ops argument, pass to remote_detach_1.
	(extended_remote_detach): Add target_ops argument, pass to
	remote_detach_1.
	(remote_parse_stop_reply): Handle new "T" stop reason "fork".
	(remote_pid_to_str): Print "process" strings for pid/0/0 ptids.
	(init_extended_remote_ops): Initialize to_follow_fork.

---
 gdb/gdbserver/gdbthread.h    |    4 +
 gdb/gdbserver/linux-low.c    |  125 +++++++++++++++++++++++++++++++++++++----
 gdb/gdbserver/remote-utils.c |   14 ++++-
 gdb/gdbserver/server.h       |    1 +
 gdb/nat/linux-ptrace.c       |   10 +++
 gdb/nat/linux-ptrace.h       |    1 +
 gdb/remote.c                 |   89 ++++++++++++++++++++++++++---
 7 files changed, 220 insertions(+), 24 deletions(-)

Comments

Don Breazeal Jan. 12, 2015, 10:49 p.m. UTC | #1
On 1/12/2015 2:39 PM, Don Breazeal wrote:
> Pedro Alves wrote:

>> I'm not even seeing a fundamental need
>> to keep this for "extended-remote" alone, given gdb nowadays supports
>> the multiprocess extensions with "target remote" too.
> 
> I agree that we should do this.  As I described in the update to patch 04
> (https://sourceware.org/ml/gdb-patches/2015-01/msg00320.html), I ran into
> several issues with implementing follow-fork for target remote.  I think
> the underlying target remote support, eliminating "gdbserver exit when
> inferior terminates", deserves its own patch, and I'd like to defer that in
> favor of making progress on the extended-remote piece.
> 
BTW, it would be helpful to me to have an explanation of why the two
remote protocols exist (remote and extended-remote) and what the
long-term plan or vision is for each of them.  Like, will they
eventually just be merged into a single protocol?  I'm pretty sure I've
had an incorrect view of this, and I haven't found an answer to "why"
by searching for it.

Thanks!
--Don
diff mbox

Patch

diff --git a/gdb/gdbserver/gdbthread.h b/gdb/gdbserver/gdbthread.h
index 8290ec1..aa77cd9 100644
--- a/gdb/gdbserver/gdbthread.h
+++ b/gdb/gdbserver/gdbthread.h
@@ -41,6 +41,10 @@  struct thread_info
   /* True if LAST_STATUS hasn't been reported to GDB yet.  */
   int status_pending_p;
 
+  /* This is used to store fork and exec event information until
+     it is reported to GDB.  */
+  struct target_waitstatus pending_follow;
+
   /* Given `while-stepping', a thread may be collecting data for more
      than one tracepoint simultaneously.  E.g.:
 
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index b1201b3..7068696 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -20,6 +20,7 @@ 
 #include "linux-low.h"
 #include "nat/linux-osdata.h"
 #include "agent.h"
+#include "tdesc.h"
 
 #include "nat/linux-nat.h"
 #include "nat/linux-waitpid.h"
@@ -364,22 +365,23 @@  linux_add_process (int pid, int attached)
 }
 
 /* Handle a GNU/Linux extended wait response.  If we see a clone
-   event, we need to add the new LWP to our list (and not report the
-   trap to higher layers).  */
+   event, we need to add the new LWP to our list (and return 0 so as
+   not to report the trap to higher layers).  */
 
-static void
+static int
 handle_extended_wait (struct lwp_info *event_child, int wstat)
 {
   int event = linux_ptrace_get_extended_event (wstat);
   struct thread_info *event_thr = get_lwp_thread (event_child);
   struct lwp_info *new_lwp;
 
-  if (event == PTRACE_EVENT_CLONE)
+  if ((event == PTRACE_EVENT_FORK) || (event == PTRACE_EVENT_CLONE))
     {
       ptid_t ptid;
       unsigned long new_pid;
       int ret, status;
 
+      /* Get the pid of the new lwp.  */
       ptrace (PTRACE_GETEVENTMSG, lwpid_of (event_thr), (PTRACE_TYPE_ARG3) 0,
 	      &new_pid);
 
@@ -399,6 +401,52 @@  handle_extended_wait (struct lwp_info *event_child, int wstat)
 	    warning ("wait returned unexpected status 0x%x", status);
 	}
 
+      if (event == PTRACE_EVENT_FORK)
+	{
+	  struct process_info *parent_proc;
+	  struct process_info *child_proc;
+	  struct lwp_info *child_lwp;
+	  struct target_desc *tdesc;
+
+	  ptid = ptid_build (new_pid, new_pid, 0);
+
+	  if (debug_threads)
+	    {
+	      debug_printf ("HEW: Got fork event from LWP %ld, "
+			    "new child is %d\n",
+			    ptid_get_lwp (ptid_of (event_thr)),
+			    ptid_get_pid (ptid));
+	    }
+
+	  /* Add the new process to the tables and clone the breakpoint
+	     lists of the parent.  We need to do this even if the new process
+	     will be detached, since we will need the process object and the
+	     breakpoints to remove any breakpoints from memory when we
+	     detach, and the host side will access registers.  */
+	  child_proc = linux_add_process (new_pid, 0);
+	  gdb_assert (child_proc != NULL);
+	  child_lwp = add_lwp (ptid);
+	  gdb_assert (child_lwp != NULL);
+	  child_lwp->stopped = 1;
+	  parent_proc = get_thread_process (event_thr);
+	  child_proc->attached = parent_proc->attached;
+	  clone_all_breakpoints (&child_proc->breakpoints,
+				 &child_proc->raw_breakpoints,
+				 parent_proc->breakpoints);
+
+	  tdesc = xmalloc (sizeof (struct target_desc));
+	  copy_target_description (tdesc, parent_proc->tdesc);
+	  child_proc->tdesc = tdesc;
+	  child_lwp->must_set_ptrace_flags = 1;
+
+	  /* Save fork info in the parent thread.  */
+	  event_thr->pending_follow.kind = TARGET_WAITKIND_FORKED;
+	  event_thr->pending_follow.value.related_pid = ptid;
+
+	  /* Report the event.  */
+	  return 0;
+	}
+
       if (debug_threads)
 	debug_printf ("HEW: Got clone event "
 		      "from LWP %ld, new child is LWP %ld\n",
@@ -448,7 +496,12 @@  handle_extended_wait (struct lwp_info *event_child, int wstat)
 	 threads, it will have a pending SIGSTOP; we may as well
 	 collect it now.  */
       linux_resume_one_lwp (event_child, event_child->stepping, 0, NULL);
+
+      /* Don't report the event.  */
+      return 1;
     }
+
+  internal_error (__FILE__, __LINE__, _("unknown ptrace event %d"), event);
 }
 
 /* Return the PC as read from the regcache of LWP, without any
@@ -1753,6 +1806,20 @@  lp_status_maybe_breakpoint (struct lwp_info *lp)
 	      || WSTOPSIG (lp->status_pending) == SIGSEGV));
 }
 
+/* Wrapper for linux_enable_event_reporting that supports disabling
+   supported events if we have determined we don't want to report
+   them.  This will not be needed once follow fork is implemented
+   for target remote as well as extended-remote.  */
+
+static void
+linux_low_enable_events (pid_t pid, int attached)
+{
+  if (!report_fork_events)
+    linux_ptrace_clear_additional_flags (PTRACE_O_TRACEFORK);
+
+  linux_enable_event_reporting (pid, attached);
+}
+
 /* Do low-level handling of the event, and check if we should go on
    and pass it to caller code.  Return the affected lwp if we are, or
    NULL otherwise.  */
@@ -1880,15 +1947,17 @@  linux_low_filter_event (ptid_t filter_ptid, int lwpid, int wstat)
     {
       struct process_info *proc = find_process_pid (pid_of (thread));
 
-      linux_enable_event_reporting (lwpid, proc->attached);
+      linux_low_enable_events (lwpid, proc->attached);
       child->must_set_ptrace_flags = 0;
     }
 
   if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGTRAP
       && linux_is_extended_waitstatus (wstat))
     {
-      handle_extended_wait (child, wstat);
-      return NULL;
+      if (handle_extended_wait (child, wstat))
+	return NULL;
+      else
+	return child;
     }
 
   if (WIFSTOPPED (wstat) && WSTOPSIG (wstat) == SIGSTOP
@@ -2486,6 +2555,18 @@  linux_stabilize_threads (void)
     }
 }
 
+/* Return non-zero if WAITSTATUS reflects an extended linux
+   event that gdbserver supports.  Otherwise, return zero.  */
+
+static int
+extended_event_reported (const struct target_waitstatus *waitstatus)
+{
+  if (waitstatus == NULL)
+    return 0;
+
+  return (waitstatus->kind == TARGET_WAITKIND_FORKED);
+}
+
 /* Wait for process, returns status.  */
 
 static ptid_t
@@ -2821,7 +2902,8 @@  retry:
 		       && !bp_explains_trap && !trace_event)
 		   || (gdb_breakpoint_here (event_child->stop_pc)
 		       && gdb_condition_true_at_breakpoint (event_child->stop_pc)
-		       && gdb_no_commands_at_breakpoint (event_child->stop_pc)));
+		       && gdb_no_commands_at_breakpoint (event_child->stop_pc))
+		   || extended_event_reported (&current_thread->pending_follow));
 
   run_breakpoint_commands (event_child->stop_pc);
 
@@ -2843,6 +2925,13 @@  retry:
 			  paddress (event_child->stop_pc),
 			  paddress (event_child->step_range_start),
 			  paddress (event_child->step_range_end));
+	  if (extended_event_reported (&current_thread->pending_follow))
+	    {
+	      char *str = target_waitstatus_to_string (ourstatus);
+	      debug_printf ("LWP %ld: extended event with waitstatus %s\n",
+			    lwpid_of (get_lwp_thread (event_child)), str);
+	      xfree (str);
+	    }
 	}
 
       /* We're not reporting this breakpoint to GDB, so apply the
@@ -2941,7 +3030,17 @@  retry:
 	unstop_all_lwps (1, event_child);
     }
 
-  ourstatus->kind = TARGET_WAITKIND_STOPPED;
+  if (extended_event_reported (&current_thread->pending_follow))
+    {
+      /* If the reported event is a fork, vfork or exec, let GDB know.  */
+      ourstatus->kind = current_thread->pending_follow.kind;
+      ourstatus->value = current_thread->pending_follow.value;
+
+      /* Reset the event lwp's waitstatus since we handled it already.  */
+      current_thread->pending_follow.kind = TARGET_WAITKIND_SPURIOUS;
+    }
+  else
+    ourstatus->kind = TARGET_WAITKIND_STOPPED;
 
   if (current_thread->last_resume_kind == resume_stop
       && WSTOPSIG (w) == SIGSTOP)
@@ -2958,7 +3057,7 @@  retry:
 	 but, it stopped for other reasons.  */
       ourstatus->value.sig = gdb_signal_from_host (WSTOPSIG (w));
     }
-  else
+  else if (ourstatus->kind == TARGET_WAITKIND_STOPPED)
     {
       ourstatus->value.sig = gdb_signal_from_host (WSTOPSIG (w));
     }
@@ -4744,8 +4843,8 @@  linux_write_memory (CORE_ADDR memaddr, const unsigned char *myaddr, int len)
 	val = val & 0xffff;
       else if (len == 3)
 	val = val & 0xffffff;
-      debug_printf ("Writing %0*x to 0x%08lx\n", 2 * ((len < 4) ? len : 4),
-		    val, (long)memaddr);
+      debug_printf ("Writing %0*x to 0x%08lx in process %d\n",
+		    2 * ((len < 4) ? len : 4), val, (long)memaddr, pid);
     }
 
   /* Fill start and end extra bytes of buffer with existing memory data.  */
@@ -6135,6 +6234,6 @@  initialize_low (void)
   initialize_low_arch ();
 
   /* Enable any extended ptrace events that are supported.  */
-  linux_ptrace_set_additional_flags (0);
+  linux_ptrace_set_additional_flags (PTRACE_O_TRACEFORK);
   linux_test_for_event_reporting ();
 }
diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index 373fc15..148b1fa 100644
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -1105,12 +1105,24 @@  prepare_resume_reply (char *buf, ptid_t ptid,
   switch (status->kind)
     {
     case TARGET_WAITKIND_STOPPED:
+    case TARGET_WAITKIND_FORKED:
       {
 	struct thread_info *saved_thread;
 	const char **regp;
 	struct regcache *regcache;
 
-	sprintf (buf, "T%02x", status->value.sig);
+	if (status->kind == TARGET_WAITKIND_FORKED && multi_process)
+	  {
+	    enum gdb_signal signal = GDB_SIGNAL_TRAP;
+	    const char *event = "fork";
+
+	    sprintf (buf, "T%02x%s:p%x.%lx;", signal, event,
+		     ptid_get_pid (status->value.related_pid),
+		     ptid_get_lwp (status->value.related_pid));
+	  }
+	else
+	  sprintf (buf, "T%02x", status->value.sig);
+
 	buf += strlen (buf);
 
 	saved_thread = current_thread;
diff --git a/gdb/gdbserver/server.h b/gdb/gdbserver/server.h
index 02d751a..98d1b3c 100644
--- a/gdb/gdbserver/server.h
+++ b/gdb/gdbserver/server.h
@@ -84,6 +84,7 @@  extern int disable_packet_qfThreadInfo;
 
 extern int run_once;
 extern int multi_process;
+extern int report_fork_events;
 extern int non_stop;
 
 extern int disable_randomization;
diff --git a/gdb/nat/linux-ptrace.c b/gdb/nat/linux-ptrace.c
index 542e762..89314b1 100644
--- a/gdb/nat/linux-ptrace.c
+++ b/gdb/nat/linux-ptrace.c
@@ -580,6 +580,16 @@  linux_ptrace_set_additional_flags (int flags)
   additional_flags = flags;
 }
 
+/* Clear FLAGS in current_ptrace_options.  This will not be needed once
+   follow fork et al are supported by target remote as well as extended-
+   remote.  */
+
+void
+linux_ptrace_clear_additional_flags (int flags)
+{
+  current_ptrace_options &= ~flags;
+}
+
 /* Extract extended ptrace event from wait status.  */
 
 int
diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h
index edbacfd..f7fe6bf 100644
--- a/gdb/nat/linux-ptrace.h
+++ b/gdb/nat/linux-ptrace.h
@@ -98,6 +98,7 @@  extern int linux_supports_traceclone (void);
 extern int linux_supports_tracevforkdone (void);
 extern int linux_supports_tracesysgood (void);
 extern void linux_ptrace_set_additional_flags (int);
+extern void linux_ptrace_clear_additional_flags (int flags);
 extern int linux_ptrace_get_extended_event (int wstat);
 extern int linux_is_extended_waitstatus (int wstat);
 
diff --git a/gdb/remote.c b/gdb/remote.c
index 891329a..172943c 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -24,6 +24,7 @@ 
 #include <fcntl.h>
 #include "inferior.h"
 #include "infrun.h"
+#include "inf-child.h"
 #include "bfd.h"
 #include "symfile.h"
 #include "target.h"
@@ -1438,7 +1439,6 @@  remote_multi_process_p (struct remote_state *rs)
   return packet_support (PACKET_multiprocess_feature) == PACKET_ENABLE;
 }
 
-#if PTRACE_FORK_EVENTS
 /* Returns true if fork events are supported.  */
 
 static int
@@ -1447,6 +1447,7 @@  remote_fork_event_p (struct remote_state *rs)
   return packet_support (PACKET_fork_event_feature) == PACKET_ENABLE;
 }
 
+#if PTRACE_FORK_EVENTS
 /* Returns true if vfork events are supported.  */
 
 static int
@@ -1456,6 +1457,53 @@  remote_vfork_event_p (struct remote_state *rs)
 }
 #endif
 
+/* Target follow-fork function for remote targets.  On entry, and
+   at return, the current inferior is the fork parent.
+
+   Note that although this is currently only used for extended-remote,
+   it is named remote_follow_fork in anticipation of using it for the
+   remote target as well.  */
+
+static int
+remote_follow_fork (struct target_ops *target, int follow_child,
+		    int detach_fork)
+{
+  struct remote_state *rs = get_remote_state ();
+
+  /* Checking the fork event is sufficient for both fork and vfork.  */
+  if (remote_fork_event_p (rs))
+    {
+      if (detach_fork && !follow_child)
+	{
+	  ptid_t child_ptid;
+	  pid_t child_pid;
+
+	  gdb_assert ((inferior_thread ()->pending_follow.kind
+		       == TARGET_WAITKIND_FORKED));
+	  child_ptid = inferior_thread ()->pending_follow.value.related_pid;
+	  child_pid = ptid_get_pid (child_ptid);
+
+	  /* Tell the remote target to detach.  */
+	  xsnprintf (rs->buf, get_remote_packet_size (), "D;%x", child_pid);
+
+	  putpkt (rs->buf);
+	  getpkt (&rs->buf, &rs->buf_size, 0);
+
+	  if (rs->buf[0] == 'O' && rs->buf[1] == 'K')
+	    ;
+	  else if (rs->buf[0] == '\0')
+	    error (_("Remote doesn't know how to detach"));
+	  else
+	    error (_("Can't detach process."));
+
+	  inferior_ptid = null_ptid;
+	  detach_inferior (child_pid);
+	  inf_child_maybe_unpush_target (target);
+	}
+    }
+  return 0;
+}
+
 /* Tokens for use by the asynchronous signal handlers for SIGINT.  */
 static struct async_signal_handler *async_sigint_remote_twice_token;
 static struct async_signal_handler *async_sigint_remote_token;
@@ -4402,10 +4450,12 @@  remote_open_1 (const char *name, int from_tty,
    die when it hits one.  */
 
 static void
-remote_detach_1 (const char *args, int from_tty, int extended)
+remote_detach_1 (struct target_ops *ops, const char *args,
+		 int from_tty, int extended)
 {
   int pid = ptid_get_pid (inferior_ptid);
   struct remote_state *rs = get_remote_state ();
+  struct thread_info *tp = first_thread_of_process (pid);
 
   if (args)
     error (_("Argument given to \"detach\" when remotely debugging."));
@@ -4442,19 +4492,28 @@  remote_detach_1 (const char *args, int from_tty, int extended)
   if (from_tty && !extended)
     puts_filtered (_("Ending remote debugging.\n"));
 
-  target_mourn_inferior ();
+  /* If doing detach-on-fork, we don't mourn, because that will delete
+     breakpoints that should be available for the child.  */
+  if (tp->pending_follow.kind != TARGET_WAITKIND_FORKED)
+    target_mourn_inferior ();
+  else
+    {
+      inferior_ptid = null_ptid;
+      detach_inferior (pid);
+      inf_child_maybe_unpush_target (ops);
+    }
 }
 
 static void
 remote_detach (struct target_ops *ops, const char *args, int from_tty)
 {
-  remote_detach_1 (args, from_tty, 0);
+  remote_detach_1 (ops, args, from_tty, 0);
 }
 
 static void
 extended_remote_detach (struct target_ops *ops, const char *args, int from_tty)
 {
-  remote_detach_1 (args, from_tty, 1);
+  remote_detach_1 (ops, args, from_tty, 1);
 }
 
 /* Same as remote_detach, but don't send the "D" packet; just disconnect.  */
@@ -5546,11 +5605,12 @@  remote_parse_stop_reply (char *buf, struct stop_reply *event)
 	     pnum and set p1 to point to the character following it.
 	     Otherwise p1 points to p.  */
 
-	  /* If this packet is an awatch packet, don't parse the 'a'
-	     as a register number.  */
+	  /* If this packet's stop reason starts with a hex digit,
+	     don't parse it as a register number.  */
 
 	  if (strncmp (p, "awatch", strlen("awatch")) != 0
-	      && strncmp (p, "core", strlen ("core") != 0))
+	      && strncmp (p, "core", strlen ("core") != 0)
+	      && strncmp (p, "fork", strlen ("fork") != 0))
 	    {
 	      /* Read the ``P'' register number.  */
 	      pnum = strtol (p, &p_temp, 16);
@@ -5602,6 +5662,11 @@  Packet: '%s'\n"),
 		  p = unpack_varlen_hex (++p1, &c);
 		  event->core = c;
 		}
+	      else if (strncmp (p, "fork", p1 - p) == 0)
+		{
+		  event->ws.value.related_pid = read_ptid (++p1, &p);
+		  event->ws.kind = TARGET_WAITKIND_FORKED;
+		}
 	      else
 		{
 		  /* Silently skip unknown optional info.  */
@@ -9413,8 +9478,11 @@  remote_pid_to_str (struct target_ops *ops, ptid_t ptid)
       if (ptid_equal (magic_null_ptid, ptid))
 	xsnprintf (buf, sizeof buf, "Thread <main>");
       else if (rs->extended && remote_multi_process_p (rs))
-	xsnprintf (buf, sizeof buf, "Thread %d.%ld",
-		   ptid_get_pid (ptid), ptid_get_lwp (ptid));
+	if (ptid_get_lwp (ptid) == 0)
+	  return normal_pid_to_str (ptid);
+	else
+	  xsnprintf (buf, sizeof buf, "Thread %d.%ld",
+		     ptid_get_pid (ptid), ptid_get_lwp (ptid));
       else
 	xsnprintf (buf, sizeof buf, "Thread %ld",
 		   ptid_get_lwp (ptid));
@@ -11662,6 +11730,7 @@  Specify the serial device it is connected to (e.g. /dev/ttya).";
   extended_remote_ops.to_kill = extended_remote_kill;
   extended_remote_ops.to_supports_disable_randomization
     = extended_remote_supports_disable_randomization;
+  extended_remote_ops.to_follow_fork = remote_follow_fork;
 }
 
 static int