XML feature description support.

	* NEWS: Mention target descriptions, "set tdesc filename",
	"unset tdesc filename", "show tdesc filename", and
	qXfer:features:read.
	* arch-utils.c (choose_architecture_for_target): New function.
	(gdbarch_info_fill): Call it.
	* target-descriptions.c (struct property): Make members non-const.
	(struct target_desc): Add arch member.
	(target_description_filename): New variable.
	(target_find_description): Try via XML first.
	(tdesc_architecture): New.
	(free_target_description, make_cleanup_free_target_description): New.
	(set_tdesc_property): Call xstrdup.
	(set_tdesc_architecture, tdesc_set_cmdlist, tdesc_show_cmdlist)
	(tdesc_unset_cmdlist, unset_tdesc_cmd, unset_tdesc_filename_cmd)
	(set_tdesc_cmd, show_tdesc_cmd, set_tdesc_filename_cmd)
	(show_tdesc_filename_cmd, _initialize_target_descriptions): New.
	* target-descriptions.h (tdesc_architecture)
	(make_cleanup_free_target_description, set_tdesc_architecture): New
	prototypes.
	* Makefile.in (SFILES): Add xml-tdesc.c.
	(COMMON_OBS): Add xml-tdesc.o.
	(target-descriptions.o): Update.
	(xml-tdesc.o): New rule.
	* xml-tdesc.c, xml-tdesc.h: New files.
	* remote.c (PACKET_qXfer_features): New enum.
	(remote_protocol_features): Add qXfer:features:read.
	(remote_xfer_partial): Handle TARGET_OBJECT_AVAILABLE_FEATURES.
	(_initialize_remote): Register qXfer:features:read.
	* target.h (enum target_object): Add TARGET_OBJECT_AVAILABLE_FEATURES.
	* features/gdb-target.dtd: New file.

	* linux-i386-low.c (the_low_target): Set arch_string.
	* linux-x86-64-low.c (the_low_target): Likewise.
	* linux-low.c (linux_arch_string): New.
	(linux_target_ops): Add it.
	* linux-low.h (struct linux_target_ops): Add arch_string.
	* server.c (write_qxfer_response): Use const void * for DATA.
	(get_features_xml): New.
	(handle_query): Handle qXfer:features:read.  Report it for qSupported.
	* target.h (struct target_ops): Add arch_string method.

	* gdb.texinfo (Target Descriptions): New section.
	(General Query Packets): Add QPassSignals anchor.  Mention
	qXfer:features:read under qSupported.  Expand mentions of
	qXfer:memory-map:read and QPassSignals.  Document
	qXfer:features:read.

1 files changed, 73 insertions, 0 deletions

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index 78768a61a91..36359553441 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -409,6 +409,75 @@ set_endian (char *ignore_args, int from_tty, struct cmd_list_element *c)
   show_endian (gdb_stdout, from_tty, NULL, NULL);
 }
 
+/* Given SELECTED, a currently selected BFD architecture, and
+   FROM_TARGET, a BFD architecture reported by the target description,
+   return what architecture to use.  Either may be NULL; if both are
+   specified, we use the more specific.  If the two are obviously
+   incompatible, warn the user.  */
+
+static const struct bfd_arch_info *
+choose_architecture_for_target (const struct bfd_arch_info *selected,
+				const struct bfd_arch_info *from_target)
+{
+  const struct bfd_arch_info *compat1, *compat2;
+
+  if (selected == NULL)
+    return from_target;
+
+  if (from_target == NULL)
+    return selected;
+
+  /* struct bfd_arch_info objects are singletons: that is, there's
+     supposed to be exactly one instance for a given machine.  So you
+     can tell whether two are equivalent by comparing pointers.  */
+  if (from_target == selected)
+    return selected;
+
+  /* BFD's 'A->compatible (A, B)' functions return zero if A and B are
+     incompatible.  But if they are compatible, it returns the 'more
+     featureful' of the two arches.  That is, if A can run code
+     written for B, but B can't run code written for A, then it'll
+     return A.
+
+     Some targets (e.g. MIPS as of 2006-12-04) don't fully
+     implement this, instead always returning NULL or the first
+     argument.  We detect that case by checking both directions.  */
+
+  compat1 = selected->compatible (selected, from_target);
+  compat2 = from_target->compatible (from_target, selected);
+
+  if (compat1 == NULL && compat2 == NULL)
+    {
+      warning (_("Selected architecture %s is not compatible "
+		 "with reported target architecture %s"),
+	       selected->printable_name, from_target->printable_name);
+      return selected;
+    }
+
+  if (compat1 == NULL)
+    return compat2;
+  if (compat2 == NULL)
+    return compat1;
+  if (compat1 == compat2)
+    return compat1;
+
+  /* If the two didn't match, but one of them was a default architecture,
+     assume the more specific one is correct.  This handles the case
+     where an executable or target description just says "mips", but
+     the other knows which MIPS variant.  */
+  if (compat1->the_default)
+    return compat2;
+  if (compat2->the_default)
+    return compat1;
+
+  /* We have no idea which one is better.  This is a bug, but not
+     a critical problem; warn the user.  */
+  warning (_("Selected architecture %s is ambiguous with "
+	     "reported target architecture %s"),
+	   selected->printable_name, from_target->printable_name);
+  return selected;
+}
+
 /* Functions to manipulate the architecture of the target */
 
 enum set_arch { set_arch_auto, set_arch_manual };
@@ -703,6 +772,10 @@ gdbarch_info_fill (struct gdbarch_info *info)
       && bfd_get_arch (info->abfd) != bfd_arch_unknown
       && bfd_get_arch (info->abfd) != bfd_arch_obscure)
     info->bfd_arch_info = bfd_get_arch_info (info->abfd);
+  /* From the target.  */
+  if (info->target_desc != NULL)
+    info->bfd_arch_info = choose_architecture_for_target
+      (info->bfd_arch_info, tdesc_architecture (info->target_desc));
   /* From the default.  */
   if (info->bfd_arch_info == NULL)
     info->bfd_arch_info = default_bfd_arch;