[patch] Detecting and printing 128-bit long double values for GDB 6.6

[Luis Machado <luisgpm at linux dot vnet dot ibm dot com>]

Hi folks,

Attached is the patch previously written by Pete Carr for correcting the
issue where GDB is unable to print the value of a 128-bit long double
variable. This patch makes GDB recognize that data type and also makes
it print the correct value with its full precision. I refreshed this
patch for GDB 6.6, in case users of this version would like to use it.

A version of the patch for GDB HEAD is being worked on and will be
submitted soon, since it requires some code changes due to a
modification in the handling of Big endian/Little endian values.

Best regards,
Luis

2007-04-23  Luis Machado  <luisgpm@br.ibm.com>

	* rs6000-tdep.c (rs6000_gdbarch_init): Set the long double format for
	powerpc64.
	* configure.host : Set the host long double format for powerpc64 to be
	a 128-bit type defined in libiberty/floatformat.c.
	* floatformat.c : Introduce default floatformat structs to describe the
	128-bit long double found on the powerpc64. Description does not fully
	describe this format which is actually a pair of 64-bit doubles. However
	we are relying on floatformat_to_doublest() recognizing that this is
	also the default host floatformat.
	* floatformat.h : Default floatformat structs for powerpc64 128-bit
	long doubles.

Index: gdb/configure.host
===================================================================
--- gdb/configure.host.orig
+++ gdb/configure.host
@@ -188,6 +188,11 @@ m68*-*-*)
 	gdb_host_double_format="&floatformat_ieee_double_big"
 	gdb_host_long_double_format="&floatformat_m68881_ext"
 	;;
+powerpc64-*-*)
+	gdb_host_float_format=0
+	gdb_host_double_format=0
+	gdb_host_long_double_format="&floatformat_ppc64_long_double_big"
+	;;
 *)
 	gdb_host_float_format=0
 	gdb_host_double_format=0
Index: gdb/rs6000-tdep.c
===================================================================
--- gdb/rs6000-tdep.c.orig
+++ gdb/rs6000-tdep.c
@@ -3391,7 +3391,19 @@ rs6000_gdbarch_init (struct gdbarch_info
   set_gdbarch_float_bit (gdbarch, 4 * TARGET_CHAR_BIT);
   set_gdbarch_double_bit (gdbarch, 8 * TARGET_CHAR_BIT);
   if (sysv_abi)
-    set_gdbarch_long_double_bit (gdbarch, 16 * TARGET_CHAR_BIT);
+    {
+      int byte_order = gdbarch_byte_order (gdbarch);
+
+      if (byte_order == BFD_ENDIAN_BIG)
+        set_gdbarch_long_double_format (gdbarch, &floatformat_ppc64_long_double_big);
+      else if (byte_order == BFD_ENDIAN_LITTLE) 
+        set_gdbarch_long_double_format (gdbarch, &floatformat_ppc64_long_double_little);
+      else
+        internal_error (__FILE__, __LINE__,
+                      _("rs6000_gdbarch_init: "
+                        "bad byte order"));
+      set_gdbarch_long_double_bit (gdbarch, 16 * TARGET_CHAR_BIT);
+    }
   else
     set_gdbarch_long_double_bit (gdbarch, 8 * TARGET_CHAR_BIT);
   set_gdbarch_char_signed (gdbarch, 0);
Index: include/floatformat.h
===================================================================
--- include/floatformat.h.orig
+++ include/floatformat.h
@@ -118,6 +118,9 @@ extern const struct floatformat floatfor
 extern const struct floatformat floatformat_ia64_spill_little;
 extern const struct floatformat floatformat_ia64_quad_big;
 extern const struct floatformat floatformat_ia64_quad_little;
+/* ppc64 long double implemented as 2 doubles */
+extern const struct floatformat floatformat_ppc64_long_double_big;
+extern const struct floatformat floatformat_ppc64_long_double_little;
 
 /* Convert from FMT to a double.
    FROM is the address of the extended float.
Index: libiberty/floatformat.c
===================================================================
--- libiberty/floatformat.c.orig
+++ libiberty/floatformat.c
@@ -106,6 +106,25 @@ const struct floatformat floatformat_iee
   floatformat_always_valid
 };
 
+/* floatformats for ppc64 long double, big and little endian.           */
+/* The layout is a pair of doubles. Don't use this description to pass  */
+/* information to get_field(). The bit size is the important thing.     */
+const struct floatformat floatformat_ppc64_long_double_big =
+{
+  floatformat_big, 128, 0, 1, 11, 1023, 2047, 12, 52, 
+  floatformat_intbit_no,
+  "floatformat_ppc64_long_double_big",
+  floatformat_always_valid
+};
+
+const struct floatformat floatformat_ppc64_long_double_little =
+{
+  floatformat_little, 128, 0, 1, 11, 1023, 2047, 12, 52, 
+  floatformat_intbit_no,
+  "floatformat_ppc64_long_double_little",
+  floatformat_always_valid
+};
+
 /* floatformat for IEEE double, little endian byte order, with big endian word
    ordering, as on the ARM.  */
 
Index: gdb/ppc-linux-tdep.c
===================================================================
--- gdb/ppc-linux-tdep.c.orig
+++ gdb/ppc-linux-tdep.c
@@ -1036,7 +1036,9 @@ ppc_linux_init_abi (struct gdbarch_info 
      Linux[sic] Standards Base says that programs that use 'long
      double' on PPC GNU/Linux are non-conformant.  */
   /* NOTE: cagney/2005-01-25: True for both 32- and 64-bit.  */
+#if 0
   set_gdbarch_long_double_bit (gdbarch, 8 * TARGET_CHAR_BIT);
+#endif
 
   if (tdep->wordsize == 4)
     {