Thread options & clone events (core + remote)

A previous patch taught GDB about a new TARGET_WAITKIND_THREAD_CLONED
event kind, and made the Linux target report clone events.

A following patch will teach Linux GDBserver to do the same thing.

However, for remote debugging, it wouldn't be ideal for GDBserver to
report every clone event to GDB, when GDB only cares about such events
in some specific situations.  Reporting clone events all the time
would be potentially chatty.  We don't enable thread create/exit
events all the time for the same reason.  Instead we have the
QThreadEvents packet.  QThreadEvents is target-wide, though.

This patch makes GDB instead explicitly request that the target
reports clone events or not, on a per-thread basis.

In order to be able to do that with GDBserver, we need a new remote
protocol feature.  Since a following patch will want to enable thread
exit events on per-thread basis too, the packet introduced here is
more generic than just for clone events.  It lets you enable/disable a
set of options at once, modelled on Linux ptrace's PTRACE_SETOPTIONS.

IOW, this commit introduces a new QThreadOptions packet, that lets you
specify a set of per-thread event options you want to enable.  The
packet accepts a list of options/thread-id pairs, similarly to vCont,
processed left to right, with the options field being a number
interpreted as a bit mask of options.  The only option defined in this
commit is GDB_THREAD_OPTION_CLONE (0x1), which ask the remote target
to report clone events.  Another patch later in the series will
introduce another option.

For example, this packet sets option "1" (clone events) on thread
p1000.2345:

  QThreadOptions;1:p1000.2345

and this clears options for all threads of process 1000, and then sets
option "1" (clone events) on thread p1000.2345:

  QThreadOptions;0:p1000.-1;1:p1000.2345

This clears options of all threads of all processes:

  QThreadOptions;0

The target reports the set of supported options by including
"QThreadOptions=<supported options>" in its qSupported response.

infrun is then tweaked to enable GDB_THREAD_OPTION_CLONE when stepping
over a breakpoint.

Unlike PTRACE_SETOPTIONS, fork/vfork/clone children do NOT inherit
their parent's thread options.  This is so that GDB can send e.g.,
"QThreadOptions;0;1:TID" without worrying about threads it doesn't
know about yet.

Documentation for this new remote protocol feature is included in a
documentation patch later in the series.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=19675
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=27830
Reviewed-By: Andrew Burgess <aburgess@redhat.com>
Change-Id: Ie41e5093b2573f14cf6ac41b0b5804eba75be37e

4 files changed, 145 insertions, 0 deletions

diff --git a/gdbserver/gdbthread.h b/gdbserver/gdbthread.h
index 493e1db..a4dff0f 100644
--- a/gdbserver/gdbthread.h
+++ b/gdbserver/gdbthread.h
@@ -80,6 +80,9 @@ struct thread_info
 
   /* Branch trace target information for this thread.  */
   struct btrace_target_info *btrace = nullptr;
+
+  /* Thread options GDB requested with QThreadOptions.  */
+  gdb_thread_options thread_options = 0;
 };
 
 extern std::list<thread_info *> all_threads;
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index 38f084b..c24a5c9 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -36,6 +36,7 @@
 #include "dll.h"
 #include "hostio.h"
 #include <vector>
+#include <unordered_map>
 #include "gdbsupport/common-inferior.h"
 #include "gdbsupport/job-control.h"
 #include "gdbsupport/environ.h"
@@ -616,6 +617,17 @@ parse_store_memtags_request (char *request, CORE_ADDR *addr, size_t *len,
   return true;
 }
 
+/* Parse thread options starting at *P and return them.  On exit,
+   advance *P past the options.  */
+
+static gdb_thread_options
+parse_gdb_thread_options (const char **p)
+{
+  ULONGEST options = 0;
+  *p = unpack_varlen_hex (*p, &options);
+  return (gdb_thread_option) options;
+}
+
 /* Handle all of the extended 'Q' packets.  */
 
 static void
@@ -897,6 +909,114 @@ handle_general_set (char *own_buf)
       return;
     }
 
+  if (startswith (own_buf, "QThreadOptions;"))
+    {
+      const char *p = own_buf + strlen ("QThreadOptions");
+
+      gdb_thread_options supported_options = target_supported_thread_options ();
+      if (supported_options == 0)
+	{
+	  /* Something went wrong -- we don't support any option, but
+	     GDB sent the packet anyway.  */
+	  write_enn (own_buf);
+	  return;
+	}
+
+      /* We could store the options directly in thread->thread_options
+	 without this map, but that would mean that a QThreadOptions
+	 packet with a wildcard like "QThreadOptions;0;3:TID" would
+	 result in the debug logs showing:
+
+	   [options for TID are now 0x0]
+	   [options for TID are now 0x3]
+
+	 It's nicer if we only print the final options for each TID,
+	 and if we only print about it if the options changed compared
+	 to the options that were previously set on the thread.  */
+      std::unordered_map<thread_info *, gdb_thread_options> set_options;
+
+      while (*p != '\0')
+	{
+	  if (p[0] != ';')
+	    {
+	      write_enn (own_buf);
+	      return;
+	    }
+	  p++;
+
+	  /* Read the options.  */
+
+	  gdb_thread_options options = parse_gdb_thread_options (&p);
+
+	  if ((options & ~supported_options) != 0)
+	    {
+	      /* GDB asked for an unknown or unsupported option, so
+		 error out.  */
+	      std::string err
+		= string_printf ("E.Unknown thread options requested: %s\n",
+				 to_string (options).c_str ());
+	      strcpy (own_buf, err.c_str ());
+	      return;
+	    }
+
+	  ptid_t ptid;
+
+	  if (p[0] == ';' || p[0] == '\0')
+	    ptid = minus_one_ptid;
+	  else if (p[0] == ':')
+	    {
+	      const char *q;
+
+	      ptid = read_ptid (p + 1, &q);
+
+	      if (p == q)
+		{
+		  write_enn (own_buf);
+		  return;
+		}
+	      p = q;
+	      if (p[0] != ';' && p[0] != '\0')
+		{
+		  write_enn (own_buf);
+		  return;
+		}
+	    }
+	  else
+	    {
+	      write_enn (own_buf);
+	      return;
+	    }
+
+	  /* Convert PID.-1 => PID.0 for ptid.matches.  */
+	  if (ptid.lwp () == -1)
+	    ptid = ptid_t (ptid.pid ());
+
+	  for_each_thread ([&] (thread_info *thread)
+	    {
+	      if (ptid_of (thread).matches (ptid))
+		set_options[thread] = options;
+	    });
+	}
+
+      for (const auto &iter : set_options)
+	{
+	  thread_info *thread = iter.first;
+	  gdb_thread_options options = iter.second;
+
+	  if (thread->thread_options != options)
+	    {
+	      threads_debug_printf ("[options for %s are now %s]\n",
+				    target_pid_to_str (ptid_of (thread)).c_str (),
+				    to_string (options).c_str ());
+
+	      thread->thread_options = options;
+	    }
+	}
+
+      write_ok (own_buf);
+      return;
+    }
+
   if (startswith (own_buf, "QStartupWithShell:"))
     {
       const char *value = own_buf + strlen ("QStartupWithShell:");
@@ -2348,6 +2468,8 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 		cs.vCont_supported = 1;
 	      else if (feature == "QThreadEvents+")
 		;
+	      else if (feature == "QThreadOptions+")
+		;
 	      else if (feature == "no-resumed+")
 		{
 		  /* GDB supports and wants TARGET_WAITKIND_NO_RESUMED
@@ -2474,6 +2596,14 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 
       strcat (own_buf, ";vContSupported+");
 
+      gdb_thread_options supported_options = target_supported_thread_options ();
+      if (supported_options != 0)
+	{
+	  char *end_buf = own_buf + strlen (own_buf);
+	  sprintf (end_buf, ";QThreadOptions=%s",
+		   phex_nz (supported_options, sizeof (supported_options)));
+	}
+
       strcat (own_buf, ";QThreadEvents+");
 
       strcat (own_buf, ";no-resumed+");
diff --git a/gdbserver/target.cc b/gdbserver/target.cc
index f8e592d..1c740bb 100644
--- a/gdbserver/target.cc
+++ b/gdbserver/target.cc
@@ -532,6 +532,12 @@ process_stratum_target::supports_vfork_events ()
   return false;
 }
 
+gdb_thread_options
+process_stratum_target::supported_thread_options ()
+{
+  return 0;
+}
+
 bool
 process_stratum_target::supports_exec_events ()
 {
diff --git a/gdbserver/target.h b/gdbserver/target.h
index f13ee40..8893e0a 100644
--- a/gdbserver/target.h
+++ b/gdbserver/target.h
@@ -276,6 +276,9 @@ public:
   /* Returns true if vfork events are supported.  */
   virtual bool supports_vfork_events ();
 
+  /* Returns the set of supported thread options.  */
+  virtual gdb_thread_options supported_thread_options ();
+
   /* Returns true if exec events are supported.  */
   virtual bool supports_exec_events ();
 
@@ -531,6 +534,9 @@ int kill_inferior (process_info *proc);
 #define target_supports_vfork_events() \
   the_target->supports_vfork_events ()
 
+#define target_supported_thread_options(options) \
+  the_target->supported_thread_options (options)
+
 #define target_supports_exec_events() \
   the_target->supports_exec_events ()