[rfc] [11/18] Cell multi-arch: Target description <compatible> infrastructure

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Hello,

this patch extends the target description infrastructure to allow a target
to define "compatible" architectures.  This is used to specify e.g. on Cell
that even though the target is PowerPC, it is compatible with executables
of the SPU architecture -- in an inferior process of PowerPC architecture,
objfiles of SPU architecture may be present as shared libraries or even
the main executable.

This is primarily required to prevent choose_architecture_for_target from 
rejecting a target description of architecture PowerPC just because a main
executable of architecture SPU was just started.

It is also a convenient means to inquire whether the current target is
a Cell system (as opposed to a regular PowerPC).

Bye,
Ulrich


ChangeLog:

	* target-descriptions.h (tdesc_compatible_p): New.
	(tdesc_add_compatible): New.
	* target-descriptions.c (arch_p): New VEC_P type.
	(struct target_desc): New member compatible.
	(free_target_description): Handle it.
	(maint_print_c_tdesc_cmd): Likewise.
	(tdesc_compatible_p): New function.
	(tdesc_add_compatible): New function.

	* xml-tdesc.c (tdesc_end_compatible): New function.
	(target_children): Handle <compatible> element.

	* arch-utils.c (choose_architecture_for_target): Accept target
	description instead of BFD architecture as input.  Query target
	description for compatible architectures.
	(gdbarch_info_fill): Update call.

doc/ChangeLog:

	* gdb.texinfo (Target Descriptions): Document <compatible> element.


Index: src/gdb/arch-utils.c
===================================================================
--- src.orig/gdb/arch-utils.c
+++ src/gdb/arch-utils.c
@@ -326,15 +326,24 @@ set_endian (char *ignore_args, int from_
 }
 
 /* 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.  */
+   TARGET_DESC, the current target description, return what
+   architecture to use.
+
+   SELECTED may be NULL, in which case we return the architecture
+   associated with TARGET_DESC.  If SELECTED specifies a variant
+   of the architecture associtated with TARGET_DESC, return the
+   more specific of the two.
+
+   If SELECTED is a different architecture, but it is accepted as
+   compatible by the target, we can use the target architecture.
+
+   If SELECTED is 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)
+choose_architecture_for_target (const struct target_desc *target_desc,
+				const struct bfd_arch_info *selected)
 {
+  const struct bfd_arch_info *from_target = tdesc_architecture (target_desc);
   const struct bfd_arch_info *compat1, *compat2;
 
   if (selected == NULL)
@@ -364,6 +373,11 @@ choose_architecture_for_target (const st
 
   if (compat1 == NULL && compat2 == NULL)
     {
+      /* BFD considers the architectures incompatible.  Check our target
+	 description whether it accepts SELECTED as compatible anyway.  */
+      if (tdesc_compatible_p (target_desc, selected))
+	return from_target;
+
       warning (_("Selected architecture %s is not compatible "
 		 "with reported target architecture %s"),
 	       selected->printable_name, from_target->printable_name);
@@ -692,7 +706,7 @@ gdbarch_info_fill (struct gdbarch_info *
   /* 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));
+			   (info->target_desc, info->bfd_arch_info);
   /* From the default.  */
   if (info->bfd_arch_info == NULL)
     info->bfd_arch_info = default_bfd_arch;
Index: src/gdb/target-descriptions.c
===================================================================
--- src.orig/gdb/target-descriptions.c
+++ src/gdb/target-descriptions.c
@@ -104,6 +104,10 @@ typedef struct tdesc_feature
 } *tdesc_feature_p;
 DEF_VEC_P(tdesc_feature_p);
 
+/* A compatible architecture from a target description.  */
+typedef const struct bfd_arch_info *arch_p;
+DEF_VEC_P(arch_p);
+
 /* A target description.  */
 
 struct target_desc
@@ -111,6 +115,9 @@ struct target_desc
   /* The architecture reported by the target, if any.  */
   const struct bfd_arch_info *arch;
 
+  /* The list of compatible architectures reported by the target.  */
+  VEC(arch_p) *compatible;
+
   /* Any architecture-specific properties specified by the target.  */
   VEC(property_s) *properties;
 
@@ -290,6 +297,28 @@ tdesc_architecture (const struct target_
 {
   return target_desc->arch;
 }
+
+/* Return non-zero if this target description is compatible
+   with the given BFD architecture.  */
+
+int
+tdesc_compatible_p (const struct target_desc *target_desc,
+		    const struct bfd_arch_info *arch)
+{
+  const struct bfd_arch_info *compat;
+  int ix;
+
+  for (ix = 0; VEC_iterate (arch_p, target_desc->compatible, ix, compat);
+       ix++)
+    {
+      if (compat == arch
+	  || arch->compatible (arch, compat)
+	  || compat->compatible (compat, arch))
+	return 1;
+    }
+
+  return 0;
+}
 
 
 /* Return 1 if this target description includes any registers.  */
@@ -885,6 +914,8 @@ free_target_description (void *arg)
     }
   VEC_free (property_s, target_desc->properties);
 
+  VEC_free (arch_p, target_desc->compatible);
+
   xfree (target_desc);
 }
 
@@ -895,6 +926,30 @@ make_cleanup_free_target_description (st
 }
 
 void
+tdesc_add_compatible (struct target_desc *target_desc,
+		      const struct bfd_arch_info *compatible)
+{
+  const struct bfd_arch_info *compat;
+  int ix;
+
+  /* If this instance of GDB is compiled without BFD support for the
+     compatible architecture, simply ignore it -- we would not be able
+     to handle it anyway.  */
+  if (compatible == NULL)
+    return;
+
+  for (ix = 0; VEC_iterate (arch_p, target_desc->compatible, ix, compat);
+       ix++)
+    if (compat == compatible)
+      internal_error (__FILE__, __LINE__,
+		      _("Attempted to add duplicate "
+			"compatible architecture \"%s\""),
+		      compatible->printable_name);
+
+  VEC_safe_push (arch_p, target_desc->compatible, compatible);
+}
+
+void
 set_tdesc_property (struct target_desc *target_desc,
 		    const char *key, const char *value)
 {
@@ -993,6 +1048,7 @@ static void
 maint_print_c_tdesc_cmd (char *args, int from_tty)
 {
   const struct target_desc *tdesc;
+  const struct bfd_arch_info *compatible;
   const char *filename, *inp;
   char *function, *outp;
   struct property *prop;
@@ -1049,6 +1105,16 @@ maint_print_c_tdesc_cmd (char *args, int
       printf_unfiltered ("\n");
     }
 
+  for (ix = 0; VEC_iterate (arch_p, tdesc->compatible, ix, compatible);
+       ix++)
+    {
+      printf_unfiltered
+	("  tdesc_add_compatible (result, bfd_scan_arch (\"%s\"));\n",
+	 compatible->printable_name);
+    }
+  if (ix)
+    printf_unfiltered ("\n");
+
   for (ix = 0; VEC_iterate (property_s, tdesc->properties, ix, prop);
        ix++)
     {
Index: src/gdb/target-descriptions.h
===================================================================
--- src.orig/gdb/target-descriptions.h
+++ src/gdb/target-descriptions.h
@@ -123,6 +123,12 @@ int tdesc_numbered_register_choices (con
 const struct bfd_arch_info *tdesc_architecture
   (const struct target_desc *);
 
+/* Return non-zero if this target description is compatible
+   with the given BFD architecture.  */
+
+int tdesc_compatible_p (const struct target_desc *,
+			const struct bfd_arch_info *);
+
 /* Return the string value of a property named KEY, or NULL if the
    property was not specified.  */
 
@@ -169,6 +175,8 @@ void set_tdesc_architecture (struct targ
 			     const struct bfd_arch_info *);
 void set_tdesc_property (struct target_desc *,
 			 const char *key, const char *value);
+void tdesc_add_compatible (struct target_desc *,
+			   const struct bfd_arch_info *);
 
 struct tdesc_feature *tdesc_create_feature (struct target_desc *tdesc,
 					    const char *name);
Index: src/gdb/xml-tdesc.c
===================================================================
--- src.orig/gdb/xml-tdesc.c
+++ src/gdb/xml-tdesc.c
@@ -106,6 +106,20 @@ tdesc_end_arch (struct gdb_xml_parser *p
   set_tdesc_architecture (data->tdesc, arch);
 }
 
+/* Handle the end of a <compatible> element and its value.  */
+
+static void
+tdesc_end_compatible (struct gdb_xml_parser *parser,
+		      const struct gdb_xml_element *element,
+		      void *user_data, const char *body_text)
+{
+  struct tdesc_parsing_data *data = user_data;
+  const struct bfd_arch_info *arch;
+
+  arch = bfd_scan_arch (body_text);
+  tdesc_add_compatible (data->tdesc, arch);
+}
+
 /* Handle the start of a <target> element.  */
 
 static void
@@ -345,6 +359,8 @@ static const struct gdb_xml_attribute ta
 static const struct gdb_xml_element target_children[] = {
   { "architecture", NULL, NULL, GDB_XML_EF_OPTIONAL,
     NULL, tdesc_end_arch },
+  { "compatible", NULL, NULL, GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
+    NULL, tdesc_end_compatible },
   { "feature", feature_attributes, feature_children,
     GDB_XML_EF_OPTIONAL | GDB_XML_EF_REPEATABLE,
     tdesc_start_feature, NULL },
Index: src/gdb/doc/gdb.texinfo
===================================================================
--- src.orig/gdb/doc/gdb.texinfo
+++ src/gdb/doc/gdb.texinfo
@@ -27586,6 +27586,7 @@ are explained further below.
 <!DOCTYPE target SYSTEM "gdb-target.dtd">
 <target version="1.0">
   @r{[}@var{architecture}@r{]}
+  @r{[}@var{compatible}@dots{}@r{]}
   @r{[}@var{feature}@dots{}@r{]}
 </target>
 @end smallexample
@@ -27641,6 +27642,26 @@ An @samp{<architecture>} element has thi
 accepted by @code{set architecture} (@pxref{Targets, ,Specifying a
 Debugging Target}).
 
+@subsection Compatible Architecture
+@cindex <compatible>
+
+A @samp{<compatible>} element has this form:
+
+@smallexample
+  <compatible>@var{arch}</compatible>
+@end smallexample
+
+@var{arch} is an architecture name from the same selection
+accepted by @code{set architecture} (@pxref{Targets, ,Specifying a
+Debugging Target}).
+
+A @samp{<compatible>} element is used to specify that the target
+is able to run binaries in some other than the main target architecture
+given by the @samp{<architecture>} element.  For example, on the
+Cell Broadband Engine, the main architecture is @code{powerpc:common}
+or @code{powerpc:common64}, but the system is able to run binaries
+in the @code{spu} architecture as well.
+
 @subsection Features
 @cindex <feature>
 
-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com