[rfc] Auto-detect MIPS 32-bit and 64-bit register packets

[Daniel Jacobowitz <drow at false dot org>]

Similar to the last patch, but for MIPS64.

This is even more useful than the amd64 patch.  If you have an i386 or amd64
ELF file, it's obvious which register layout to expect.  If you have a MIPS
binary, it may be considerably less clear.  For one thing, mips_isa_regsize
is currently set to return 64-bit for binaries based on the BFD architecture
rather than the ELF class; so o32 binaries optimized for a 64-bit processor
cause GDB to expect 64-bit registers!  For another, I have a gdbserver port
for MIPS64 coming up next; if GDB can handle receiving the 64-bit register
layout from it, then a single gdbserver can be used (in most cases) for
all three MIPS ABIs.

For MIPS the problem addressed by this patch is encountered considerably
more frequently than the amd64 equivalent.  It got to be a FAQ on the
linux-mips list at one point, for using kgdb - kernels are often an example
of a 32-bit binary optimized for a particular 64-bit processor, when a
64-bit kernel isn't justified.

I'd like to thank MontaVista for funding this bit of work, which I hope
will be useful to MIPS GNU/Linux developers!  And hopefully stop me
having to explain the manual "set architecture" workaround on linux-mips,
too.

Tested manually on mips-linux and mips64-linux with various combinations
of stubs.  Depends on the earlier patches in this group, of course - I'll
wait to commit this until I see how those are received.

-- 
Daniel Jacobowitz
CodeSourcery

2006-11-09  Daniel Jacobowitz  <dan@codesourcery.com>

	* Makefile.in (mips-tdep.o, target-descriptions.o): Update.
	* target-descriptions.c (struct property): New.
	(struct target_desc): Add properties member.
	(tdesc_property, set_tdesc_property): New.
	* target-descriptions.h (tdesc_property, set_tdesc_property):
	Declare.
	* mips-tdep.c (PROPERTY_GP32, PROPERTY_GP64): New constants.
	(struct gdbarch_tdep): Add register_size_valid_p and register_size.
	(mips_isa_regsize): Use them.
	(mips_register_g_packet_guesses): New.
	(mips_gdbarch_init): Call it.  If a target description is supplied,
	check for internal properties.

---
 gdb/Makefile.in           |    4 +-
 gdb/mips-tdep.c           |   71 ++++++++++++++++++++++++++++++++++++++++++++++
 gdb/target-descriptions.c |   48 +++++++++++++++++++++++++++++++
 gdb/target-descriptions.h |    8 +++++
 4 files changed, 129 insertions(+), 2 deletions(-)

Index: src/gdb/Makefile.in
===================================================================
--- src.orig/gdb/Makefile.in	2006-11-09 10:41:32.000000000 -0500
+++ src/gdb/Makefile.in	2006-11-09 10:42:40.000000000 -0500
@@ -2377,7 +2377,7 @@ mips-tdep.o: mips-tdep.c $(defs_h) $(gdb
 	$(block_h) $(reggroups_h) $(opcode_mips_h) $(elf_mips_h) \
 	$(elf_bfd_h) $(symcat_h) $(sim_regno_h) $(dis_asm_h) \
 	$(frame_unwind_h) $(frame_base_h) $(trad_frame_h) $(infcall_h) \
-	$(floatformat_h)
+	$(floatformat_h) $(remote_h) $(target_descriptions_h)
 mipsv4-nat.o: mipsv4-nat.c $(defs_h) $(inferior_h) $(gdbcore_h) $(target_h) \
 	$(regcache_h) $(gregset_h)
 memory-map.o: memory-map.c $(defs_h) $(memory_map_h) $(xml_support_h) \
@@ -2765,7 +2765,7 @@ target.o: target.c $(defs_h) $(gdb_strin
 	$(gdb_wait_h) $(dcache_h) $(regcache_h) $(gdb_assert_h) $(gdbcore_h) \
 	$(exceptions_h) $(target_descriptions_h)
 target-descriptions.o: target-descriptions.c $(defs_h) $(arch_utils_h) \
-	$(target_h) $(target_descriptions_h) $(gdb_assert_h)
+	$(target_h) $(target_descriptions_h) $(vec_h) $(gdb_assert_h)
 target-memory.o: target-memory.c $(defs_h) $(vec_h) $(target_h) \
 	$(memory_map_h) $(gdb_assert_h)
 thread.o: thread.c $(defs_h) $(symtab_h) $(frame_h) $(inferior_h) \
Index: src/gdb/target-descriptions.c
===================================================================
--- src.orig/gdb/target-descriptions.c	2006-11-09 10:41:24.000000000 -0500
+++ src/gdb/target-descriptions.c	2006-11-09 10:41:46.000000000 -0500
@@ -26,15 +26,26 @@
 #include "arch-utils.h"
 #include "target.h"
 #include "target-descriptions.h"
+#include "vec.h"
 
 #include "gdb_assert.h"
 
 /* Types.  */
 
+typedef struct property
+{
+  const char *key;
+  const char *value;
+} property_s;
+DEF_VEC_O(property_s);
+
 struct target_desc
 {
   /* The architecture reported by the target, if any.  */
   const struct bfd_arch_info *arch;
+
+  /* Any architecture-specific properties specified by the target.  */
+  VEC(property_s) *properties;
 };
 
 /* Global state.  These variables are associated with the current
@@ -133,6 +144,23 @@ tdesc_architecture (const struct target_
   return target_desc->arch;
 }
 
+/* Return the string value of a property named KEY, or NULL if the
+   property was not specified.  */
+
+const char *
+tdesc_property (const struct target_desc *target_desc, const char *key)
+{
+  struct property *prop;
+  int ix;
+
+  for (ix = 0; VEC_iterate (property_s, target_desc->properties, ix, prop);
+       ix++)
+    if (strcmp (prop->key, key) == 0)
+      return prop->value;
+
+  return NULL;
+}
+
 /* Methods for constructing a target description.  */
 
 struct target_desc *
@@ -147,3 +175,23 @@ set_tdesc_architecture (struct target_de
 {
   target_desc->arch = arch;
 }
+
+void
+set_tdesc_property (struct target_desc *target_desc,
+		    const char *key, const char *value)
+{
+  struct property *prop, new_prop;
+  int ix;
+
+  gdb_assert (key != NULL && value != NULL);
+
+  for (ix = 0; VEC_iterate (property_s, target_desc->properties, ix, prop);
+       ix++)
+    if (strcmp (prop->key, key) == 0)
+      internal_error (__FILE__, __LINE__,
+		      _("Attempted to add duplicate property \"%s\""), key);
+
+  new_prop.key = key;
+  new_prop.value = value;
+  VEC_safe_push (property_s, target_desc->properties, &new_prop);
+}
Index: src/gdb/target-descriptions.h
===================================================================
--- src.orig/gdb/target-descriptions.h	2006-11-09 10:41:24.000000000 -0500
+++ src/gdb/target-descriptions.h	2006-11-09 10:41:46.000000000 -0500
@@ -51,10 +51,18 @@ const struct target_desc *target_current
 const struct bfd_arch_info *tdesc_architecture
   (const struct target_desc *);
 
+/* Return the string value of a property named KEY, or NULL if the
+   property was not specified.  */
+
+const char *tdesc_property (const struct target_desc *,
+			    const char *key);
+
 /* Methods for constructing a target description.  */
 
 struct target_desc *allocate_target_description (void);
 void set_tdesc_architecture (struct target_desc *,
 			     const struct bfd_arch_info *);
+void set_tdesc_property (struct target_desc *,
+			 const char *key, const char *value);
 
 #endif /* TARGET_DESCRIPTIONS_H */
Index: src/gdb/mips-tdep.c
===================================================================
--- src.orig/gdb/mips-tdep.c	2006-11-09 10:34:47.000000000 -0500
+++ src/gdb/mips-tdep.c	2006-11-09 10:41:46.000000000 -0500
@@ -55,6 +55,8 @@
 #include "trad-frame.h"
 #include "infcall.h"
 #include "floatformat.h"
+#include "remote.h"
+#include "target-descriptions.h"
 
 static const struct objfile_data *mips_pdr_data;
 
@@ -119,6 +121,11 @@ static enum mips_fpu_type mips_fpu_type 
 
 static int mips_debug = 0;
 
+/* Properties (for struct target_desc) describing the g/G packet
+   layout.  */
+#define PROPERTY_GP32 "internal: transfers-32bit-registers"
+#define PROPERTY_GP64 "internal: transfers-64bit-registers"
+
 /* MIPS specific per-architecture information */
 struct gdbarch_tdep
 {
@@ -141,6 +148,13 @@ struct gdbarch_tdep
   const struct mips_regnum *regnum;
   /* Register names table for the current register set.  */
   const char **mips_processor_reg_names;
+
+  /* The size of register data available from the target, if known.
+     This doesn't quite obsolete the manual
+     mips64_transfers_32bit_regs_p, since that is documented to force
+     left alignment even for big endian (very strange).  */
+  int register_size_valid_p;
+  int register_size;
 };
 
 static int
@@ -245,6 +259,13 @@ mips_abi (struct gdbarch *gdbarch)
 int
 mips_isa_regsize (struct gdbarch *gdbarch)
 {
+  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+
+  /* If we know how big the registers are, use that size.  */
+  if (tdep->register_size_valid_p)
+    return tdep->register_size;
+
+  /* Fall back to the previous behavior.  */
   return (gdbarch_bfd_arch_info (gdbarch)->bits_per_word
 	  / gdbarch_bfd_arch_info (gdbarch)->bits_per_byte);
 }
@@ -4711,6 +4732,37 @@ global_mips_abi (void)
   internal_error (__FILE__, __LINE__, _("unknown ABI string"));
 }
 
+static void
+mips_register_g_packet_guesses (struct gdbarch *gdbarch)
+{
+  static struct target_desc *tdesc_gp32, *tdesc_gp64;
+
+  if (tdesc_gp32 == NULL)
+    {
+      /* Create feature sets with the appropriate properties.  The values
+	 are not important.  */
+
+      tdesc_gp32 = allocate_target_description ();
+      set_tdesc_property (tdesc_gp32, PROPERTY_GP32, "");
+
+      tdesc_gp64 = allocate_target_description ();
+      set_tdesc_property (tdesc_gp64, PROPERTY_GP64, "");
+    }
+
+  /* If the size matches the set of 32-bit or 64-bit integer registers,
+     assume that's what we've got.  */
+  register_remote_g_packet_guess (gdbarch, 38 * 4, tdesc_gp32);
+  register_remote_g_packet_guess (gdbarch, 38 * 8, tdesc_gp64);
+
+  /* If the size matches the full set of registers GDB traditionally
+     knows about, including floating point, for either 32-bit or
+     64-bit, assume that's what we've got.  */
+  register_remote_g_packet_guess (gdbarch, 90 * 4, tdesc_gp32);
+  register_remote_g_packet_guess (gdbarch, 90 * 8, tdesc_gp64);
+
+  /* Otherwise we don't have a useful guess.  */
+}
+
 static struct gdbarch *
 mips_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 {
@@ -4885,6 +4937,23 @@ mips_gdbarch_init (struct gdbarch_info i
   tdep->found_abi = found_abi;
   tdep->mips_abi = mips_abi;
   tdep->mips_fpu_type = fpu_type;
+  tdep->register_size_valid_p = 0;
+  tdep->register_size = 0;
+
+  if (info.target_desc)
+    {
+      /* Some useful properties can be inferred from the target.  */
+      if (tdesc_property (info.target_desc, PROPERTY_GP32) != NULL)
+	{
+	  tdep->register_size_valid_p = 1;
+	  tdep->register_size = 4;
+	}
+      else if (tdesc_property (info.target_desc, PROPERTY_GP64) != NULL)
+	{
+	  tdep->register_size_valid_p = 1;
+	  tdep->register_size = 8;
+	}
+    }
 
   /* Initially set everything according to the default ABI/ISA.  */
   set_gdbarch_short_bit (gdbarch, 16);
@@ -5152,6 +5221,8 @@ mips_gdbarch_init (struct gdbarch_info i
 
   set_gdbarch_single_step_through_delay (gdbarch, mips_single_step_through_delay);
 
+  mips_register_g_packet_guesses (gdbarch);
+
   /* Hook in OS ABI-specific overrides, if they have been registered.  */
   gdbarch_init_osabi (info, gdbarch);