Identify remote fork event support

This patch implements a mechanism for GDB to determine whether fork
events are supported in gdbserver.  This is a preparatory patch for
remote fork and exec event support.

Two new RSP packets are defined to represent fork and vfork event
support.  These packets are used just like PACKET_multiprocess_feature
to denote whether the corresponding event is supported.  GDB sends
fork-events+ and vfork-events+ to gdbserver to inquire about fork
event support.  If the response enables these packets, then GDB
knows that gdbserver supports the corresponding events and will
enable them.

Target functions used to query for support are included along with
each new packet.

In order for gdbserver to know whether the events are supported at the
point where the qSupported packet arrives, the code in nat/linux-ptrace.c
had to be reorganized.  Previously it would test for fork/exec event
support, then enable the events using the pid of the inferior.  When the
qSupported packet arrives there may not be an inferior.  So the mechanism
was split into two parts: a function that checks whether the events are
supported, called when gdbserver starts up, and another that enables the
events when the inferior stops for the first time.

Another gdbserver change was to add some global variables similar to
multi_process, one per new packet.  These are used to control whether
the corresponding fork events are enabled.  If GDB does not inquire
about the event support in the qSupported packet, then gdbserver will
not set these "report the event" flags.  If the flags are not set, the
events are ignored like they were in the past.  Thus, gdbserver will
never send fork event notification to an older GDB that doesn't
recognize fork events.

Tested on Ubuntu x64, native/remote/extended-remote, and as part of
subsequent patches in the series.

gdb/gdbserver/ChangeLog:

        * linux-low.c (linux_supports_fork_events): New function.
        (linux_supports_vfork_events): New function.
        (linux_target_ops): Initialize new structure members.
        (initialize_low): Call linux_check_ptrace_features.
        * lynx-low.c (lynx_target_ops): Initialize new structure
        members.
        * server.c (report_fork_events, report_vfork_events):
        New global flags.
        (handle_query): Add new features to qSupported packet and
        response.
        (captured_main): Initialize new global variables.
        * target.h (struct target_ops) <supports_fork_events>:
        New member.
        <supports_vfork_events>: New member.
        (target_supports_fork_events): New macro.
        (target_supports_vfork_events): New macro.
        * win32-low.c (win32_target_ops): Initialize new structure
        members.

gdb/ChangeLog:

        * nat/linux-ptrace.c (linux_check_ptrace_features): Change
        from static to extern.
        * nat/linux-ptrace.h (linux_check_ptrace_features): Declare.
        * remote.c (anonymous enum): <PACKET_fork_event_feature,
        * PACKET_vfork_event_feature>: New enumeration constants.
        (remote_protocol_features): Add table entries for new packets.
        (remote_query_supported): Add new feature queries to qSupported
        packet.
        (_initialize_remote): Exempt new packets from the requirement
        to have 'set remote' commands.

6 files changed, 81 insertions, 0 deletions

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 94146b8..a37051d 100644
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,24 @@
+2015-05-12  Don Breazeal  <donb@codesourcery.com>
+
+	* linux-low.c (linux_supports_fork_events): New function.
+	(linux_supports_vfork_events): New function.
+	(linux_target_ops): Initialize new structure members.
+	(initialize_low): Call linux_check_ptrace_features.
+	* lynx-low.c (lynx_target_ops): Initialize new structure
+	members.
+	* server.c (report_fork_events, report_vfork_events):
+	New global flags.
+	(handle_query): Add new features to qSupported packet and
+	response.
+	(captured_main): Initialize new global variables.
+	* target.h (struct target_ops) <supports_fork_events>:
+	New member.
+	<supports_vfork_events>: New member.
+	(target_supports_fork_events): New macro.
+	(target_supports_vfork_events): New macro.
+	* win32-low.c (win32_target_ops): Initialize new structure
+	members.
+
 2015-05-12  Gary Benson <gbenson@redhat.com>
 
 	* server.c (handle_qxfer_exec_file): Use current process
diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index bc76ffc..1724b54 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5438,6 +5438,22 @@ linux_supports_multi_process (void)
   return 1;
 }
 
+/* Check if fork events are supported.  */
+
+static int
+linux_supports_fork_events (void)
+{
+  return linux_supports_tracefork ();
+}
+
+/* Check if vfork events are supported.  */
+
+static int
+linux_supports_vfork_events (void)
+{
+  return linux_supports_tracefork ();
+}
+
 static int
 linux_supports_disable_randomization (void)
 {
@@ -6411,6 +6427,8 @@ static struct target_ops linux_target_ops = {
   linux_async,
   linux_start_non_stop,
   linux_supports_multi_process,
+  linux_supports_fork_events,
+  linux_supports_vfork_events,
 #ifdef USE_THREAD_DB
   thread_db_handle_monitor_command,
 #else
@@ -6488,4 +6506,6 @@ initialize_low (void)
   sigaction (SIGCHLD, &sigchld_action, NULL);
 
   initialize_low_arch ();
+
+  linux_check_ptrace_features ();
 }
diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c
index 364c79f..f087416 100644
--- a/gdb/gdbserver/lynx-low.c
+++ b/gdb/gdbserver/lynx-low.c
@@ -762,6 +762,8 @@ static struct target_ops lynx_target_ops = {
   NULL,  /* async */
   NULL,  /* start_non_stop */
   NULL,  /* supports_multi_process */
+  NULL,  /* supports_fork_events */
+  NULL,  /* supports_vfork_events */
   NULL,  /* handle_monitor_command */
 };
 
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 174ab39..1544e99 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -57,6 +57,8 @@ static int exit_requested;
 int run_once;
 
 int multi_process;
+int report_fork_events;
+int report_vfork_events;
 int non_stop;
 int swbreak_feature;
 int hwbreak_feature;
@@ -2046,6 +2048,18 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 		  if (target_supports_stopped_by_hw_breakpoint ())
 		    hwbreak_feature = 1;
 		}
+	      else if (strcmp (p, "fork-events+") == 0)
+		{
+		  /* GDB supports and wants fork events if possible.  */
+		  if (target_supports_fork_events ())
+		    report_fork_events = 1;
+		}
+	      else if (strcmp (p, "vfork-events+") == 0)
+		{
+		  /* GDB supports and wants vfork events if possible.  */
+		  if (target_supports_vfork_events ())
+		    report_vfork_events = 1;
+		}
 	      else
 		target_process_qsupported (p);
 
@@ -2096,6 +2110,12 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
       if (target_supports_multi_process ())
 	strcat (own_buf, ";multiprocess+");
 
+      if (target_supports_fork_events ())
+	strcat (own_buf, ";fork-events+");
+
+      if (target_supports_vfork_events ())
+	strcat (own_buf, ";vfork-events+");
+
       if (target_supports_non_stop ())
 	strcat (own_buf, ";QNonStop+");
 
@@ -3472,6 +3492,8 @@ captured_main (int argc, char *argv[])
 
       noack_mode = 0;
       multi_process = 0;
+      report_fork_events = 0;
+      report_vfork_events = 0;
       /* Be sure we're out of tfind mode.  */
       current_traceframe = -1;
       cont_thread = null_ptid;
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index b3d08cd..697b223 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -281,6 +281,12 @@ struct target_ops
   /* Returns true if the target supports multi-process debugging.  */
   int (*supports_multi_process) (void);
 
+  /* Returns true if fork events are supported.  */
+  int (*supports_fork_events) (void);
+
+  /* Returns true if vfork events are supported.  */
+  int (*supports_vfork_events) (void);
+
   /* If not NULL, target-specific routine to process monitor command.
      Returns 1 if handled, or 0 to perform default processing.  */
   int (*handle_monitor_command) (char *);
@@ -420,6 +426,14 @@ void set_target_ops (struct target_ops *);
 
 int kill_inferior (int);
 
+#define target_supports_fork_events() \
+  (the_target->supports_fork_events ? \
+   (*the_target->supports_fork_events) () : 0)
+
+#define target_supports_vfork_events() \
+  (the_target->supports_vfork_events ? \
+   (*the_target->supports_vfork_events) () : 0)
+
 #define detach_inferior(pid) \
   (*the_target->detach) (pid)
 
diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
index 6cf56bd..a58f963 100644
--- a/gdb/gdbserver/win32-low.c
+++ b/gdb/gdbserver/win32-low.c
@@ -1831,6 +1831,8 @@ static struct target_ops win32_target_ops = {
   NULL, /* async */
   NULL, /* start_non_stop */
   NULL, /* supports_multi_process */
+  NULL, /* supports_fork_events */
+  NULL, /* supports_vfork_events */
   NULL, /* handle_monitor_command */
   NULL, /* core_of_thread */
   NULL, /* read_loadmap */