Extended-remote follow-exec

This patch implements support for exec events on extended-remote Linux
targets.  Follow-exec-mode and rerun behave as expected.  Catchpoints and
test updates are implemented in subsequent patches.

This patch was derived from a patch posted last October:
https://sourceware.org/ml/gdb-patches/2014-10/msg00877.html.
It was originally based on some work done by Luis Machado in 2013.

IMPLEMENTATION
----------------
Exec events are enabled via ptrace options.

When an exec event is detected by gdbserver, the existing process
data, along with all its associated lwp and thread data, is deleted
and replaced by data for a new single-threaded process.  The new
process data is initialized with the appropriate parts of the state
of the execing process.  This approach takes care of several potential
pitfalls, including:

 * deleting the data for an execing non-leader thread before any
   wait/sigsuspend occurs
 * correctly initializing the architecture of the execed process

We then report the exec event using a new RSP stop reason, "exec".

When GDB receives an "exec" event, it saves the status in the event
structure's target_waitstatus field, like what is done for remote fork
events.  Because the original and execed programs may have different
architectures, we skip parsing the section of the stop reply packet
that contains register data.  The register data will be retrieved
later after the inferior's architecture has been set up by
infrun.c:follow_exec.

At that point the exec event is handled by the existing event handling
in GDB.  However, a few changes were necessary so that
infrun.c:follow_exec could accommodate the remote target.

 * Where follow-exec-mode "new" is handled, we now call
   add_inferior_with_spaces instead of add_inferior with separate calls
   to set up the program and address spaces.  The motivation for this
   is that add_inferior_with_spaces also sets up the initial architecture
   for the inferior, which is needed later by target_find_description
   when it calls target_gdbarch.

 * We call a new target function, target_follow_exec.  This function
   allows us to store the execd_pathname in the inferior, instead of
   using the static string remote_exec_file from remote.c.  The static
   string didn't work for follow-exec-mode "new", since once you switched
   to the execed program, the original remote exec-file was lost.  The
   execd_pathname is now stored in the inferior's program space as a
   REGISTRY field.  All of the requisite mechanisms for this are
   defined in remote.c.

gdb/gdbserver/ChangeLog:

	* linux-low.c (linux_mourn): Static declaration.
	(linux_arch_setup): Move in front of
	handle_extended_wait.
	(linux_arch_setup_thread): New function.
	(handle_extended_wait): Handle exec events.  Call
	linux_arch_setup_thread.  Make event_lwp argument a
	pointer-to-a-pointer.
	(check_zombie_leaders): Do not check stopped threads.
	(linux_low_ptrace_options): Add PTRACE_O_TRACEEXEC.
	(linux_low_filter_event): Add lwp and thread for exec'ing
	non-leader thread if leader thread has been deleted.
	Refactor code into linux_arch_setup_thread and call it.
	Pass child lwp pointer by reference to handle_extended_wait.
	(linux_wait_for_event_filtered): Update comment.
	(linux_wait_1): Prevent clobbering exec event status.
	(linux_supports_exec_events): New function.
	(linux_target_ops) <supports_exec_events>: Initialize new member.
	* lynx-low.c (lynx_target_ops) <supports_exec_events>: Initialize
	new member.
	* remote-utils.c (prepare_resume_reply): New stop reason 'exec'.
	* server.c (report_exec_events): New global variable.
	(handle_query): Handle qSupported query for exec-events feature.
	(captured_main): Initialize report_exec_events.
	* server.h (report_exec_events): Declare new global variable.
	* target.h (struct target_ops) <supports_exec_events>: New
	member.
	(target_supports_exec_events): New macro.
	* win32-low.c (win32_target_ops) <supports_exec_events>:
	Initialize new member.

gdb/ChangeLog:

	* infrun.c (follow_exec): Use process-style ptid for
	exec message.  Call add_inferior_with_spaces and
	target_follow_exec.
	* nat/linux-ptrace.c (linux_supports_traceexec): New function.
	* nat/linux-ptrace.h (linux_supports_traceexec): Declare.
	* remote.c (remote_pspace_data): New static variable.
	(remote_pspace_data_cleanup): New function.
	(get_remote_exec_file): New function.
	(set_remote_exec_file_1): New function.
	(set_remote_exec_file): New function.
	(show_remote_exec_file): New function.
	(remote_exec_file): Delete static variable.
	(anonymous enum) <PACKET_exec_event_feature> New
	enumeration constant.
	(remote_protocol_features): Add entry for exec-events feature.
	(remote_query_supported): Add client side of qSupported query
	for exec-events feature.
	(remote_follow_exec): New function.
	(remote_parse_stop_reply): Handle 'exec' stop reason.
	(extended_remote_run, extended_remote_create_inferior): Call
	get_remote_exec_file and set_remote_exec_file_1.
	(init_extended_remote_ops) <to_follow_exec>: Initialize new
	member.
	(_initialize_remote): Call
	register_program_space_data_with_cleanup.  Call
	add_packet_config_cmd for remote exec-events feature.
	Modify call to add_setshow_string_noescape_cmd for exec-file
	to use new functions set_remote_exec_file and
	show_remote_exec_file.
	* target-debug.h, target-delegates.c: Regenerated.
	* target.c (target_follow_exec): New function.
	* target.h (struct target_ops) <to_follow_exec>: New member.
	(target_follow_exec): Declare new function.

1 files changed, 140 insertions, 8 deletions

diff --git a/gdb/remote.c b/gdb/remote.c
index e4d3edf..59004f9 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -75,6 +75,15 @@
 static char *target_buf;
 static long target_buf_size;
 
+/* Per-program-space data key.  */
+static const struct program_space_data *remote_pspace_data;
+
+/* The variable registered as the control variable used by the
+   remote exec-file commands.  While the remote exec-file setting is
+   per-program-space, the set/show machinery uses this as the 
+   location of the remote exec-file value.  */
+static char *remote_exec_file_var;
+
 /* The size to align memory write packets, when practical.  The protocol
    does not guarantee any alignment, and gdb will generate short
    writes and unaligned writes, but even as a best-effort attempt this
@@ -619,6 +628,63 @@ get_remote_state (void)
   return get_remote_state_raw ();
 }
 
+/* Cleanup routine for the remote module's pspace data.  */
+
+static void
+remote_pspace_data_cleanup (struct program_space *pspace, void *arg)
+{
+  char *remote_exec_file = arg;
+
+  xfree (remote_exec_file);
+}
+
+/* Fetch the remote exec-file from the current program space.  */
+
+static const char *
+get_remote_exec_file (void)
+{
+  char *remote_exec_file;
+
+  remote_exec_file = program_space_data (current_program_space,
+					 remote_pspace_data);
+  if (remote_exec_file == NULL)
+    return "";
+
+  return remote_exec_file;
+}
+
+/* Set the remote exec file for PSPACE.  */
+
+static void
+set_pspace_remote_exec_file (struct program_space *pspace,
+			char *remote_exec_file)
+{
+  char *old_file = program_space_data (pspace, remote_pspace_data);
+
+  xfree (old_file);
+  set_program_space_data (pspace, remote_pspace_data,
+			  xstrdup (remote_exec_file));
+}
+
+/* The "set/show remote exec-file" set command hook.  */
+
+static void
+set_remote_exec_file (char *ignored, int from_tty,
+		      struct cmd_list_element *c)
+{
+  gdb_assert (remote_exec_file_var != NULL);
+  set_pspace_remote_exec_file (current_program_space, remote_exec_file_var);
+}
+
+/* The "set/show remote exec-file" show command hook.  */
+
+static void
+show_remote_exec_file (struct ui_file *file, int from_tty,
+		       struct cmd_list_element *cmd, const char *value)
+{
+  fprintf_filtered (file, "%s\n", remote_exec_file_var);
+}
+
 static int
 compare_pnums (const void *lhs_, const void *rhs_)
 {
@@ -901,10 +967,6 @@ static unsigned int remote_address_size;
 
 static int remote_async_terminal_ours_p;
 
-/* The executable file to use for "run" on the remote side.  */
-
-static char *remote_exec_file = "";
-
 
 /* User configurable variables for the number of characters in a
    memory read/write packet.  MIN (rsa->remote_packet_size,
@@ -1401,6 +1463,9 @@ enum {
   /* Support for the Qbtrace-conf:pt:size packet.  */
   PACKET_Qbtrace_conf_pt_size,
 
+  /* Support for exec events.  */
+  PACKET_exec_event_feature,
+
   PACKET_MAX
 };
 
@@ -4279,6 +4344,8 @@ static const struct protocol_feature remote_protocol_features[] = {
     PACKET_fork_event_feature },
   { "vfork-events", PACKET_DISABLE, remote_supported_packet,
     PACKET_vfork_event_feature },
+  { "exec-events", PACKET_DISABLE, remote_supported_packet,
+    PACKET_exec_event_feature },
   { "Qbtrace-conf:pt:size", PACKET_DISABLE, remote_supported_packet,
     PACKET_Qbtrace_conf_pt_size }
 };
@@ -4368,6 +4435,9 @@ remote_query_supported (void)
 	  if (packet_set_cmd_state (PACKET_vfork_event_feature)
 	      != AUTO_BOOLEAN_FALSE)
 	    q = remote_query_supported_append (q, "vfork-events+");
+	  if (packet_set_cmd_state (PACKET_exec_event_feature)
+	      != AUTO_BOOLEAN_FALSE)
+	    q = remote_query_supported_append (q, "exec-events+");
 	}
 
       q = reconcat (q, "qSupported:", q, (char *) NULL);
@@ -4779,6 +4849,24 @@ remote_follow_fork (struct target_ops *ops, int follow_child,
   return 0;
 }
 
+/* Target follow-exec function for remote targets.  Save EXECD_PATHNAME
+   in the program space of the new inferior.  On entry and at return the
+   current inferior is the exec'ing inferior.  INF is the new exec'd
+   inferior, which may be the same as the exec'ing inferior unless
+   follow-exec-mode is "new".  */
+
+static void
+remote_follow_exec (struct target_ops *ops,
+		    struct inferior *inf, char *execd_pathname)
+{
+  /* We know that this is a target file name, so if it has the "target:"
+     prefix we strip it off before saving it in the program space.  */
+  if (is_target_filename (execd_pathname))
+    execd_pathname += strlen (TARGET_SYSROOT_PREFIX);
+
+  set_pspace_remote_exec_file (inf->pspace, execd_pathname);
+}
+
 /* Same as remote_detach, but don't send the "D" packet; just disconnect.  */
 
 static void
@@ -5977,6 +6065,7 @@ remote_parse_stop_reply (char *buf, struct stop_reply *event)
   struct remote_arch_state *rsa = get_remote_arch_state ();
   ULONGEST addr;
   char *p;
+  int skipregs = 0;
 
   event->ptid = null_ptid;
   event->rs = get_remote_state ();
@@ -6089,11 +6178,42 @@ Packet: '%s'\n"),
 	      event->ws.kind = TARGET_WAITKIND_VFORK_DONE;
 	      p = skip_to_semicolon (p1 + 1);
 	    }
+	  else if (strncmp (p, "exec", p1 - p) == 0)
+	    {
+	      ULONGEST ignored;
+	      char pathname[PATH_MAX];
+	      int pathlen;
+
+	      /* Determine the length of the execd pathname.  */
+	      p = unpack_varlen_hex (++p1, &ignored);
+	      pathlen = (p - p1) / 2;
+
+	      /* Save the pathname for event reporting and for
+		 the next run command.  */
+	      hex2bin (p1, (gdb_byte *) pathname, pathlen);
+	      pathname[pathlen] = '\0';
+
+	      /* This is freed during event handling.  */
+	      event->ws.value.execd_pathname = xstrdup (pathname);
+	      event->ws.kind = TARGET_WAITKIND_EXECD;
+
+	      /* Skip the registers included in this packet, since
+		 they may be for an architecture different from the
+		 one used by the original program.  */
+	      skipregs = 1;
+	    }
 	  else
 	    {
 	      ULONGEST pnum;
 	      char *p_temp;
 
+	      if (skipregs)
+		{
+		  p = skip_to_semicolon (p1 + 1);
+		  p++;
+		  continue;
+		}
+
 	      /* Maybe a real ``P'' register number.  */
 	      p_temp = unpack_varlen_hex (p, &pnum);
 	      /* If the first invalid character is the colon, we got a
@@ -8593,6 +8713,7 @@ extended_remote_run (char *args)
 {
   struct remote_state *rs = get_remote_state ();
   int len;
+  const char *remote_exec_file = get_remote_exec_file ();
 
   /* If the user has disabled vRun support, or we have detected that
      support is not available, do not try it.  */
@@ -8665,6 +8786,7 @@ extended_remote_create_inferior (struct target_ops *ops,
   int run_worked;
   char *stop_reply;
   struct remote_state *rs = get_remote_state ();
+  const char *remote_exec_file = get_remote_exec_file ();
 
   /* If running asynchronously, register the target file descriptor
      with the event loop.  */
@@ -12662,6 +12784,7 @@ Specify the serial device it is connected to (e.g. /dev/ttya).";
   extended_remote_ops.to_supports_disable_randomization
     = extended_remote_supports_disable_randomization;
   extended_remote_ops.to_follow_fork = remote_follow_fork;
+  extended_remote_ops.to_follow_exec = remote_follow_exec;
   extended_remote_ops.to_insert_fork_catchpoint
     = remote_insert_fork_catchpoint;
   extended_remote_ops.to_remove_fork_catchpoint
@@ -12893,6 +13016,10 @@ _initialize_remote (void)
   remote_g_packet_data_handle =
     gdbarch_data_register_pre_init (remote_g_packet_data_init);
 
+  remote_pspace_data
+    = register_program_space_data_with_cleanup (NULL,
+						remote_pspace_data_cleanup);
+
   /* Initialize the per-target state.  At the moment there is only one
      of these, not one per target.  Only one target is active at a
      time.  */
@@ -13272,6 +13399,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
   add_packet_config_cmd (&remote_protocol_packets[PACKET_Qbtrace_conf_pt_size],
        "Qbtrace-conf:pt:size", "btrace-conf-pt-size", 0);
 
+  add_packet_config_cmd (&remote_protocol_packets[PACKET_exec_event_feature],
+			 "exec-event-feature", "exec-event-feature", 0);
+
   /* Assert that we've registered "set remote foo-packet" commands
      for all packet configs.  */
   {
@@ -13340,12 +13470,14 @@ Transfer files to and from the remote target system."),
 	   _("Delete a remote file."),
 	   &remote_cmdlist);
 
-  remote_exec_file = xstrdup ("");
   add_setshow_string_noescape_cmd ("exec-file", class_files,
-				   &remote_exec_file, _("\
+				   &remote_exec_file_var, _("\
 Set the remote pathname for \"run\""), _("\
-Show the remote pathname for \"run\""), NULL, NULL, NULL,
-				   &remote_set_cmdlist, &remote_show_cmdlist);
+Show the remote pathname for \"run\""), NULL,
+				   set_remote_exec_file,
+				   show_remote_exec_file,
+				   &remote_set_cmdlist,
+				   &remote_show_cmdlist);
 
   add_setshow_boolean_cmd ("range-stepping", class_run,
 			   &use_range_stepping, _("\