Add gdbarch callback to provide formats for debug info float types

At this point, all TYPE_CODE_FLT types carry their floating-point format,
except for those creating from reading DWARF or stabs debug info.  Those
will be addressed by this commit.

The main issue here is that we actually have to determine which floating-
point format to use.  Currently, we only have the type length as input
to this decision.  In the future, we may hopefully get --at least in
DWARF-- additional information to help disambiguate multiple different
formats of the same length.  For now, we can still look at the type name
as a hint.

This decision logic is encapsulated in a gdbarch callback to allow
platform-specific overrides.  The default implementation use the same
logic (compare type length against the various gdbarch_..._bit sizes)
that is currently implemented in floatformat_from_length.

With this commit, all platforms still use the default logic, so there
should be no actual change in behavior.  A follow-on commit will add
support for __float128 on Intel and Power.

Once dwarf2read.c and stabsread.c make use of the new callback to
determine floating-point formats, we're now sure every TYPE_CODE_FLT
type will always carry its format.  The commit therefore adds asserts
to verify_floatformat to ensure new code will continue to always
provide formats, and removes the code in floatformat_from_type that
used to handle types with a NULL TYPE_FLOATFORMAT.

gdb/ChangeLog:

	* gdbarch.sh (floatformat_for_type): New gdbarch callback.
	* gdbarch.h, gdbarch.c: Re-generate.
	* arch-utils.h (default_floatformat_for_type): New prototype.
	* arch-utils.c (default_floatformat_for_type): New function.

	* doublest.c (floatformat_from_length): Remove.
	(floatformat_from_type): Assume TYPE_FLOATFORMAT is non-NULL.
	* gdbtypes.c (verify_floatformat): Require non-NULL format.

	* dwarf2read.c (dwarf2_init_float_type): New function.
	(read_base_type): Use it.
	* stabsread.c (dbx_init_float_type): New function.
	(read_sun_floating_type): Use it.
	(read_range_type): Likewise.

Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>

10 files changed, 141 insertions, 68 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1dbddac..f269c3c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,22 @@
 2016-09-05  Ulrich Weigand  <uweigand@de.ibm.com>
 
+	* gdbarch.sh (floatformat_for_type): New gdbarch callback.
+	* gdbarch.h, gdbarch.c: Re-generate.
+	* arch-utils.h (default_floatformat_for_type): New prototype.
+	* arch-utils.c (default_floatformat_for_type): New function.
+
+	* doublest.c (floatformat_from_length): Remove.
+	(floatformat_from_type): Assume TYPE_FLOATFORMAT is non-NULL.
+	* gdbtypes.c (verify_floatformat): Require non-NULL format.
+
+	* dwarf2read.c (dwarf2_init_float_type): New function.
+	(read_base_type): Use it.
+	* stabsread.c (dbx_init_float_type): New function.
+	(read_sun_floating_type): Use it.
+	(read_range_type): Likewise.
+
+2016-09-05  Ulrich Weigand  <uweigand@de.ibm.com>
+
 	* ada-lang.c (ada_language_arch_info): Use gdbarch-provided
 	platform ABI floating-point formats for built-in types.
 	* d-lang.c (build_d_types): Likewise.
diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index 53121bc..776dabc 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -241,6 +241,34 @@ legacy_virtual_frame_pointer (struct gdbarch *gdbarch,
   *frame_offset = 0;
 }
 
+/* Return a floating-point format for a floating-point variable of
+   length LEN in bits.  If non-NULL, NAME is the name of its type.
+   If no suitable type is found, return NULL.  */
+
+const struct floatformat **
+default_floatformat_for_type (struct gdbarch *gdbarch,
+			      const char *name, int len)
+{
+  const struct floatformat **format = NULL;
+
+  if (len == gdbarch_half_bit (gdbarch))
+    format = gdbarch_half_format (gdbarch);
+  else if (len == gdbarch_float_bit (gdbarch))
+    format = gdbarch_float_format (gdbarch);
+  else if (len == gdbarch_double_bit (gdbarch))
+    format = gdbarch_double_format (gdbarch);
+  else if (len == gdbarch_long_double_bit (gdbarch))
+    format = gdbarch_long_double_format (gdbarch);
+  /* On i386 the 'long double' type takes 96 bits,
+     while the real number of used bits is only 80,
+     both in processor and in memory.
+     The code below accepts the real bit size.  */
+  else if (gdbarch_long_double_format (gdbarch) != NULL
+	   && len == gdbarch_long_double_format (gdbarch)[0]->totalsize)
+    format = gdbarch_long_double_format (gdbarch);
+
+  return format;
+}
 
 int
 generic_convert_register_p (struct gdbarch *gdbarch, int regnum,
diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
index ad3f126..bbb0878 100644
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -95,6 +95,11 @@ int cannot_register_not (struct gdbarch *gdbarch, int regnum);
 
 extern gdbarch_virtual_frame_pointer_ftype legacy_virtual_frame_pointer;
 
+/* Default implementation of gdbarch_floatformat_for_type.  */
+extern const struct floatformat **
+  default_floatformat_for_type (struct gdbarch *gdbarch,
+				const char *name, int len);
+
 extern CORE_ADDR generic_skip_trampoline_code (struct frame_info *frame,
 					       CORE_ADDR pc);
 
diff --git a/gdb/doublest.c b/gdb/doublest.c
index 088037e..943a9f6 100644
--- a/gdb/doublest.c
+++ b/gdb/doublest.c
@@ -770,52 +770,8 @@ floatformat_from_doublest (const struct floatformat *fmt,
 }
 
 
-/* Return a floating-point format for a floating-point variable of
-   length LEN.  If no suitable floating-point format is found, an
-   error is thrown.
-
-   We need this functionality since information about the
-   floating-point format of a type is not always available to GDB; the
-   debug information typically only tells us the size of a
-   floating-point type.
-
-   FIXME: kettenis/2001-10-28: In many places, particularly in
-   target-dependent code, the format of floating-point types is known,
-   but not passed on by GDB.  This should be fixed.  */
-
-static const struct floatformat *
-floatformat_from_length (struct gdbarch *gdbarch, int len)
-{
-  const struct floatformat *format;
-
-  if (len * TARGET_CHAR_BIT == gdbarch_half_bit (gdbarch))
-    format = gdbarch_half_format (gdbarch)
-	       [gdbarch_byte_order (gdbarch)];
-  else if (len * TARGET_CHAR_BIT == gdbarch_float_bit (gdbarch))
-    format = gdbarch_float_format (gdbarch)
-	       [gdbarch_byte_order (gdbarch)];
-  else if (len * TARGET_CHAR_BIT == gdbarch_double_bit (gdbarch))
-    format = gdbarch_double_format (gdbarch)
-	       [gdbarch_byte_order (gdbarch)];
-  else if (len * TARGET_CHAR_BIT == gdbarch_long_double_bit (gdbarch))
-    format = gdbarch_long_double_format (gdbarch)
-	       [gdbarch_byte_order (gdbarch)];
-  /* On i386 the 'long double' type takes 96 bits,
-     while the real number of used bits is only 80,
-     both in processor and in memory.
-     The code below accepts the real bit size.  */ 
-  else if ((gdbarch_long_double_format (gdbarch) != NULL)
-	   && (len * TARGET_CHAR_BIT
-               == gdbarch_long_double_format (gdbarch)[0]->totalsize))
-    format = gdbarch_long_double_format (gdbarch)
-	       [gdbarch_byte_order (gdbarch)];
-  else
-    format = NULL;
-  if (format == NULL)
-    error (_("Unrecognized %d-bit floating-point type."),
-	   len * TARGET_CHAR_BIT);
-  return format;
-}
+/* Return the floating-point format for a floating-point variable of
+   type TYPE.  */
 
 const struct floatformat *
 floatformat_from_type (const struct type *type)
@@ -824,11 +780,8 @@ floatformat_from_type (const struct type *type)
   const struct floatformat *fmt;
 
   gdb_assert (TYPE_CODE (type) == TYPE_CODE_FLT);
-  if (TYPE_FLOATFORMAT (type) != NULL)
-    fmt = TYPE_FLOATFORMAT (type)[gdbarch_byte_order (gdbarch)];
-  else
-    fmt = floatformat_from_length (gdbarch, TYPE_LENGTH (type));
-
+  gdb_assert (TYPE_FLOATFORMAT (type));
+  fmt = TYPE_FLOATFORMAT (type)[gdbarch_byte_order (gdbarch)];
   gdb_assert (TYPE_LENGTH (type) >= floatformat_totalsize_bytes (fmt));
   return fmt;
 }
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 746290e..40ee66d 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -14757,6 +14757,27 @@ read_typedef (struct die_info *die, struct dwarf2_cu *cu)
   return this_type;
 }
 
+/* Allocate a floating-point type of size BITS and name NAME.  Pass NAME_HINT
+   (which may be different from NAME) to the architecture back-end to allow
+   it to guess the correct format if necessary.  */
+
+static struct type *
+dwarf2_init_float_type (struct objfile *objfile, int bits, const char *name,
+			const char *name_hint)
+{
+  struct gdbarch *gdbarch = get_objfile_arch (objfile);
+  const struct floatformat **format;
+  struct type *type;
+
+  format = gdbarch_floatformat_for_type (gdbarch, name_hint, bits);
+  if (format)
+    type = init_float_type (objfile, bits, name, format);
+  else
+    type = init_type (objfile, TYPE_CODE_ERROR, bits / TARGET_CHAR_BIT, name);
+
+  return type;
+}
+
 /* Find a representation of a given base type and install
    it in the TYPE field of the die.  */
 
@@ -14797,14 +14818,14 @@ read_base_type (struct die_info *die, struct dwarf2_cu *cu)
 	type = init_boolean_type (objfile, bits, 1, name);
 	break;
       case DW_ATE_complex_float:
-	type = init_float_type (objfile, bits / 2, NULL, NULL);
+	type = dwarf2_init_float_type (objfile, bits / 2, NULL, name);
 	type = init_complex_type (objfile, name, type);
 	break;
       case DW_ATE_decimal_float:
 	type = init_decfloat_type (objfile, bits, name);
 	break;
       case DW_ATE_float:
-	type = init_float_type (objfile, bits, name, NULL);
+	type = dwarf2_init_float_type (objfile, bits, name, name);
 	break;
       case DW_ATE_signed:
 	type = init_integer_type (objfile, bits, 0, name);
diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
index af7359e..4d8ef18 100644
--- a/gdb/gdbarch.c
+++ b/gdb/gdbarch.c
@@ -176,6 +176,7 @@ struct gdbarch
   const struct floatformat ** double_format;
   int long_double_bit;
   const struct floatformat ** long_double_format;
+  gdbarch_floatformat_for_type_ftype *floatformat_for_type;
   int ptr_bit;
   int addr_bit;
   int dwarf2_addr_size;
@@ -376,6 +377,7 @@ gdbarch_alloc (const struct gdbarch_info *info,
   gdbarch->float_bit = 4*TARGET_CHAR_BIT;
   gdbarch->double_bit = 8*TARGET_CHAR_BIT;
   gdbarch->long_double_bit = 8*TARGET_CHAR_BIT;
+  gdbarch->floatformat_for_type = default_floatformat_for_type;
   gdbarch->ptr_bit = gdbarch->int_bit;
   gdbarch->char_signed = -1;
   gdbarch->virtual_frame_pointer = legacy_virtual_frame_pointer;
@@ -522,6 +524,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of long_double_bit, invalid_p == 0 */
   if (gdbarch->long_double_format == 0)
     gdbarch->long_double_format = floatformats_ieee_double;
+  /* Skip verify of floatformat_for_type, invalid_p == 0 */
   /* Skip verify of ptr_bit, invalid_p == 0 */
   if (gdbarch->addr_bit == 0)
     gdbarch->addr_bit = gdbarch_ptr_bit (gdbarch);
@@ -973,6 +976,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
                       "gdbarch_dump: float_format = %s\n",
                       pformat (gdbarch->float_format));
   fprintf_unfiltered (file,
+                      "gdbarch_dump: floatformat_for_type = <%s>\n",
+                      host_address_to_string (gdbarch->floatformat_for_type));
+  fprintf_unfiltered (file,
                       "gdbarch_dump: fp0_regnum = %s\n",
                       plongest (gdbarch->fp0_regnum));
   fprintf_unfiltered (file,
@@ -1729,6 +1735,23 @@ set_gdbarch_long_double_format (struct gdbarch *gdbarch,
   gdbarch->long_double_format = long_double_format;
 }
 
+const struct floatformat **
+gdbarch_floatformat_for_type (struct gdbarch *gdbarch, const char *name, int length)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->floatformat_for_type != NULL);
+  if (gdbarch_debug >= 2)
+    fprintf_unfiltered (gdb_stdlog, "gdbarch_floatformat_for_type called\n");
+  return gdbarch->floatformat_for_type (gdbarch, name, length);
+}
+
+void
+set_gdbarch_floatformat_for_type (struct gdbarch *gdbarch,
+                                  gdbarch_floatformat_for_type_ftype floatformat_for_type)
+{
+  gdbarch->floatformat_for_type = floatformat_for_type;
+}
+
 int
 gdbarch_ptr_bit (struct gdbarch *gdbarch)
 {
diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index bc0f692..cd01718 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -187,6 +187,14 @@ extern void set_gdbarch_long_double_bit (struct gdbarch *gdbarch, int long_doubl
 extern const struct floatformat ** gdbarch_long_double_format (struct gdbarch *gdbarch);
 extern void set_gdbarch_long_double_format (struct gdbarch *gdbarch, const struct floatformat ** long_double_format);
 
+/* Returns the floating-point format to be used for values of length LENGTH.
+   NAME, if non-NULL, is the type name, which may be used to distinguish
+   different target formats of the same length. */
+
+typedef const struct floatformat ** (gdbarch_floatformat_for_type_ftype) (struct gdbarch *gdbarch, const char *name, int length);
+extern const struct floatformat ** gdbarch_floatformat_for_type (struct gdbarch *gdbarch, const char *name, int length);
+extern void set_gdbarch_floatformat_for_type (struct gdbarch *gdbarch, gdbarch_floatformat_for_type_ftype *floatformat_for_type);
+
 /* For most targets, a pointer on the target and its representation as an
    address in GDB have the same size and "look the same".  For such a
    target, you need only set gdbarch_ptr_bit and gdbarch_addr_bit
diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index d8e0eeb..1663156 100755
--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -383,6 +383,11 @@ v:const struct floatformat **:double_format:::::floatformats_ieee_double::pforma
 v:int:long_double_bit:::8 * sizeof (long double):8*TARGET_CHAR_BIT::0
 v:const struct floatformat **:long_double_format:::::floatformats_ieee_double::pformat (gdbarch->long_double_format)
 
+# Returns the floating-point format to be used for values of length LENGTH.
+# NAME, if non-NULL, is the type name, which may be used to distinguish
+# different target formats of the same length.
+m:const struct floatformat **:floatformat_for_type:const char *name, int length:name, length:0:default_floatformat_for_type::0
+
 # For most targets, a pointer on the target and its representation as an
 # address in GDB have the same size and "look the same".  For such a
 # target, you need only set gdbarch_ptr_bit and gdbarch_addr_bit
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index b7b638e..ad890ca 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -2712,21 +2712,16 @@ set_type_code (struct type *type, enum type_code code)
 static int
 verify_floatformat (int bit, const struct floatformat **floatformats)
 {
+  gdb_assert (floatformats != NULL);
+  gdb_assert (floatformats[0] != NULL && floatformats[1] != NULL);
+
   if (bit == -1)
-    {
-      gdb_assert (floatformats != NULL);
-      gdb_assert (floatformats[0] != NULL && floatformats[1] != NULL);
-      bit = floatformats[0]->totalsize;
-    }
+    bit = floatformats[0]->totalsize;
   gdb_assert (bit >= 0);
 
-  if (floatformats != NULL)
-    {
-      size_t len = bit / TARGET_CHAR_BIT;
-
-      gdb_assert (len >= floatformat_totalsize_bytes (floatformats[0]));
-      gdb_assert (len >= floatformat_totalsize_bytes (floatformats[1]));
-    }
+  size_t len = bit / TARGET_CHAR_BIT;
+  gdb_assert (len >= floatformat_totalsize_bytes (floatformats[0]));
+  gdb_assert (len >= floatformat_totalsize_bytes (floatformats[1]));
 
   return bit;
 }
diff --git a/gdb/stabsread.c b/gdb/stabsread.c
index 3bad6ac..e8ebadd 100644
--- a/gdb/stabsread.c
+++ b/gdb/stabsread.c
@@ -353,6 +353,24 @@ dbx_alloc_type (int typenums[2], struct objfile *objfile)
   return (*type_addr);
 }
 
+/* Allocate a floating-point type of size BITS.  */
+
+static struct type *
+dbx_init_float_type (struct objfile *objfile, int bits)
+{
+  struct gdbarch *gdbarch = get_objfile_arch (objfile);
+  const struct floatformat **format;
+  struct type *type;
+
+  format = gdbarch_floatformat_for_type (gdbarch, NULL, bits);
+  if (format)
+    type = init_float_type (objfile, bits, NULL, format);
+  else
+    type = init_type (objfile, TYPE_CODE_ERROR, bits / TARGET_CHAR_BIT, NULL);
+
+  return type;
+}
+
 /* for all the stabs in a given stab vector, build appropriate types 
    and fix their symbols in given symbol vector.  */
 
@@ -3847,11 +3865,11 @@ read_sun_floating_type (char **pp, int typenums[2], struct objfile *objfile)
   if (details == NF_COMPLEX || details == NF_COMPLEX16
       || details == NF_COMPLEX32)
     {
-      rettype = init_float_type (objfile, nbits / 2, NULL, NULL);
+      rettype = dbx_init_float_type (objfile, nbits / 2);
       return init_complex_type (objfile, NULL, rettype);
     }
 
-  return init_float_type (objfile, nbits, NULL, NULL);
+  return dbx_init_float_type (objfile, nbits);
 }
 
 /* Read a number from the string pointed to by *PP.
@@ -4138,7 +4156,7 @@ read_range_type (char **pp, int typenums[2], int type_size,
   if (n3 == 0 && n2 > 0)
     {
       struct type *float_type
-	= init_float_type (objfile, n2 * TARGET_CHAR_BIT, NULL, NULL);
+	= dbx_init_float_type (objfile, n2 * TARGET_CHAR_BIT);
 
       if (self_subrange)
 	return init_complex_type (objfile, NULL, float_type);