gdbserver: Fix qSupported:xmlRegisters=i386;UnknownFeature+ handling

The target_process_qsupported method is called for each qSupported
feature that the common code does not recognize.  The only current
implementation, for x86 Linux (x86_linux_process_qsupported), assumes
that it either is called with the "xmlRegisters=i386" feature, or that
it is isn't called at all, indicating the connected GDB predates x86
XML descriptions.

That's a bad assumption however.  If GDB sends in a new/unknown (to
core gdbserver) feature after "xmlRegisters=i386", say, something like
qSupported:xmlRegisters=i386;UnknownFeature+, then when
target_process_qsupported is called for "UnknownFeature+",
x86_linux_process_qsupported clears the 'use_xml' global and calls
x86_linux_update_xmltarget, and gdbserver ends up _not_ reporting a
XML description...

This commit changes the target_process_qsupported API to instead pass
down a vector of unprocessed qSupported features in one go.

(There's an early call to target_process_qsupported(NULL) that
indicates "starting qSupported processing".  There's no matching call
to mark the end of processing, though.  I first fixed this by passing
(char *)-1 to indicate that, and adjusted the x86 backend to only
clear 'use_xml' when qSupported processing starts, and then only call
x86_linux_update_xmltarget() when (char *)-1 was passed.  However, I
wasn't that happy with the hack and came up this alternative version.)

gdb/gdbserver/ChangeLog:
2015-11-19  Pedro Alves  <palves@redhat.com>

	* linux-low.c (linux_process_qsupported): Change prototype.
	Adjust.
	* linux-low.h (struct linux_target_ops) <process_qsupported>:
	Change prototype.
	* linux-x86-low.c (x86_linux_process_qsupported): Change prototype
	and adjust to loop over all features.
	* server.c (handle_query) <qSupported>: Adjust to call
	target_process_qsupported once, passing it a vector of unprocessed
	features.
	* target.h (struct target_ops) <process_qsupported>: Change
	prototype.
	(target_process_qsupported): Adjust.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,18 @@
+2015-11-19  Pedro Alves  <palves@redhat.com>
+
+	* linux-low.c (linux_process_qsupported): Change prototype.
+	Adjust.
+	* linux-low.h (struct linux_target_ops) <process_qsupported>:
+	Change prototype.
+	* linux-x86-low.c (x86_linux_process_qsupported): Change prototype
+	and adjust to loop over all features.
+	* server.c (handle_query) <qSupported>: Adjust to call
+	target_process_qsupported once, passing it a vector of unprocessed
+	features.
+	* target.h (struct target_ops) <process_qsupported>: Change
+	prototype.
+	(target_process_qsupported): Adjust.
+
 2015-11-19  Pedro Alves  <palves@redhat.com>
 
 	* configure.ac (ERROR_ON_WARNING): Don't check whether in C++

gdb/gdbserver/linux-low.c

@@ -6128,10 +6128,10 @@ linux_read_loadmap (const char *annex, CORE_ADDR offset,
 #endif /* defined PT_GETDSBT || defined PTRACE_GETFDPIC */
 
 static void
-linux_process_qsupported (const char *query)
+linux_process_qsupported (char **features, int count)
 {
   if (the_low_target.process_qsupported != NULL)
-    the_low_target.process_qsupported (query);
+    the_low_target.process_qsupported (features, count);
 }
 
 static int

gdb/gdbserver/linux-low.h

@@ -199,7 +199,7 @@ struct linux_target_ops
   void (*prepare_to_resume) (struct lwp_info *);
 
   /* Hook to support target specific qSupported.  */
-  void (*process_qsupported) (const char *);
+  void (*process_qsupported) (char **, int count);
 
   /* Returns true if the low target supports tracepoints.  */
   int (*supports_tracepoints) (void);

gdb/gdbserver/linux-x86-low.c

@@ -1356,29 +1356,35 @@ x86_linux_update_xmltarget (void)
    PTRACE_GETREGSET.  */
 
 static void
-x86_linux_process_qsupported (const char *query)
+x86_linux_process_qsupported (char **features, int count)
 {
+  int i;
+
   /* Return if gdb doesn't support XML.  If gdb sends "xmlRegisters="
      with "i386" in qSupported query, it supports x86 XML target
      descriptions.  */
   use_xml = 0;
-  if (query != NULL && startswith (query, "xmlRegisters="))
+  for (i = 0; i < count; i++)
     {
-      char *copy = xstrdup (query + 13);
-      char *p;
+      const char *feature = features[i];
 
-      for (p = strtok (copy, ","); p != NULL; p = strtok (NULL, ","))
+      if (startswith (feature, "xmlRegisters="))
 	{
-	  if (strcmp (p, "i386") == 0)
+	  char *copy = xstrdup (feature + 13);
+	  char *p;
+
+	  for (p = strtok (copy, ","); p != NULL; p = strtok (NULL, ","))
 	    {
-	      use_xml = 1;
-	      break;
+	      if (strcmp (p, "i386") == 0)
+		{
+		  use_xml = 1;
+		  break;
+		}
 	    }
-	} 
 
-      free (copy);
+	  free (copy);
+	}
     }
-
   x86_linux_update_xmltarget ();
 }
 

gdb/gdbserver/server.c

@@ -2054,9 +2054,6 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
       char *p = &own_buf[10];
       int gdb_supports_qRelocInsn = 0;
 
-      /* Start processing qSupported packet.  */
-      target_process_qsupported (NULL);
-
       /* Process each feature being provided by GDB.  The first
 	 feature will follow a ':', and latter features will follow
 	 ';'.  */
@@ -2064,6 +2061,7 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 	{
 	  char **qsupported = NULL;
 	  int count = 0;
+	  int unknown = 0;
 	  int i;
 
 	  /* Two passes, to avoid nested strtok calls in
@@ -2128,11 +2126,20 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
 	      else if (strcmp (p, "vContSupported+") == 0)
 		vCont_supported = 1;
 	      else
-		target_process_qsupported (p);
-
-	      free (p);
+		{
+		  /* Move the unknown features all together.  */
+		  qsupported[i] = NULL;
+		  qsupported[unknown] = p;
+		  unknown++;
+		}
 	    }
 
+	  /* Give the target backend a chance to process the unknown
+	     features.  */
+	  target_process_qsupported (qsupported, unknown);
+
+	  for (i = 0; i < count; i++)
+	    free (qsupported[i]);
 	  free (qsupported);
 	}
 

gdb/gdbserver/target.h

@@ -306,8 +306,9 @@ struct target_ops
   int (*read_loadmap) (const char *annex, CORE_ADDR offset,
 		       unsigned char *myaddr, unsigned int len);
 
-  /* Target specific qSupported support.  */
-  void (*process_qsupported) (const char *);
+  /* Target specific qSupported support.  FEATURES is an array of
+     features with COUNT elements.  */
+  void (*process_qsupported) (char **features, int count);
 
   /* Return 1 if the target supports tracepoints, 0 (or leave the
      callback NULL) otherwise.  */
@@ -519,11 +520,11 @@ int kill_inferior (int);
   (the_target->supports_multi_process ? \
    (*the_target->supports_multi_process) () : 0)
 
-#define target_process_qsupported(query)		\
+#define target_process_qsupported(features, count)	\
   do							\
     {							\
       if (the_target->process_qsupported)		\
-	the_target->process_qsupported (query);		\
+	the_target->process_qsupported (features, count); \
     } while (0)
 
 #define target_supports_tracepoints()			\