[rfa/doc] Add version to XML target descriptions

[Daniel Jacobowitz <drow@false.org>]

Carlos O'Donell suggested that our XML descriptions should have a
format version number in them, which may simplify future changes.
This patch adds a marker.  The use of #FIXED means that omitting the
version is OK - GDB will assume it's the version that GDB knows about.
But if you include the version, and GDB changes to a new version, then
the version marker will cause GDB to give a sensible error (or allow a
hypothetical future GDB to handle multiple versions of the format).

Eli, does the documentation update look OK?

Once this patch is committed I will update the copy on the web site
too.

-- 
Daniel Jacobowitz
CodeSourcery

2007-06-12  Daniel Jacobowitz  <dan@codesourcery.com>

	* gdb.texinfo (Target Description Format): Add version attribute
	for <target>.

	* xml-tdesc.c (tdesc_start_target): New.
	(target_attributes): New.
	(tdesc_elements): Use it.
	* features/gdb-target.dtd: Add #FIXED version attribute for
	<target>.

Index: gdb/doc/gdb.texinfo
===================================================================
--- gdb/doc/gdb.texinfo	(revision 173463)
+++ gdb/doc/gdb.texinfo	(working copy)
@@ -25478,7 +25478,7 @@ target, or to warn you if you connect to
 Here is a simple target description:
 
 @smallexample
-<target>
+<target version="1.0">
   <architecture>i386:x86-64</architecture>
 </target>
 @end smallexample
@@ -25494,7 +25494,7 @@ are explained further below.
 @smallexample
 <?xml version="1.0"?>
 <!DOCTYPE target SYSTEM "gdb-target.dtd">
-<target>
+<target version="1.0">
   @r{[}@var{architecture}@r{]}
   @r{[}@var{feature}@dots{}@r{]}
 </target>
@@ -25505,7 +25505,11 @@ The description is generally insensitive
 breaks, under the usual common-sense rules.  The XML version
 declaration and document type declaration can generally be omitted
 (@value{GDBN} does not require them), but specifying them may be
-useful for XML validation tools.
+useful for XML validation tools.  The version attribute for
+@samp{<target>} may also be omitted, but we recommend
+including it; if future versions of @value{GDBN} use an incompatible
+revision of @file{gdb-target.dtd}, they will detect and report
+the version mismatch.
 
 @subsection Inclusion
 @cindex target descriptions, inclusion
Index: gdb/xml-tdesc.c
===================================================================
--- gdb/xml-tdesc.c	(revision 173463)
+++ gdb/xml-tdesc.c	(working copy)
@@ -126,6 +126,22 @@ tdesc_end_arch (struct gdb_xml_parser *p
   set_tdesc_architecture (data->tdesc, arch);
 }
 
+/* Handle the start of a <target> element.  */
+
+static void
+tdesc_start_target (struct gdb_xml_parser *parser,
+		    const struct gdb_xml_element *element,
+		    void *user_data, VEC(gdb_xml_value_s) *attributes)
+{
+  struct tdesc_parsing_data *data = user_data;
+  char *version = VEC_index (gdb_xml_value_s, attributes, 0)->value;
+
+  if (strcmp (version, "1.0") != 0)
+    gdb_xml_error (parser,
+		   _("Target description has unsupported version \"%s\""),
+		   version);
+}
+
 /* Handle the start of a <feature> element.  */
 
 static void
@@ -599,6 +615,11 @@ static const struct gdb_xml_element feat
   { NULL, NULL, NULL, GDB_XML_EF_NONE, NULL, NULL }
 };
 
+static const struct gdb_xml_attribute target_attributes[] = {
+  { "version", GDB_XML_AF_NONE, NULL, NULL },
+  { NULL, GDB_XML_AF_NONE, NULL, NULL }
+};
+
 static const struct gdb_xml_element target_children[] = {
   { "architecture", NULL, NULL, GDB_XML_EF_OPTIONAL,
     NULL, tdesc_end_arch },
@@ -611,8 +632,8 @@ static const struct gdb_xml_element targ
 };
 
 static const struct gdb_xml_element tdesc_elements[] = {
-  { "target", NULL, target_children, GDB_XML_EF_NONE,
-    NULL, NULL },
+  { "target", target_attributes, target_children, GDB_XML_EF_NONE,
+    tdesc_start_target, NULL },
   { NULL, NULL, NULL, GDB_XML_EF_NONE, NULL, NULL }
 };
 
Index: gdb/features/gdb-target.dtd
===================================================================
--- gdb/features/gdb-target.dtd	(revision 173463)
+++ gdb/features/gdb-target.dtd	(working copy)
@@ -7,6 +7,8 @@
 <!-- The root element of a GDB target description is <target>.  -->
 
 <!ELEMENT target	(architecture?, feature*)>
+<!ATTLIST target
+	version		CDATA	#FIXED "1.0">
 
 <!ELEMENT architecture	(#PCDATA)>