PowerPC: fix _Float128 type output string

PowerPC supports two 128-bit floating point formats, the IBM long double
and IEEE 128-bit float.  The issue is the DWARF information does not
distinguish between the two.  There have been proposals of how to extend
the DWARF information as discussed in

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104194

but has not been fully implemented.

GCC introduced the _Float128 internal type as a work around for the issue.
The workaround is not transparent to GDB.  The internal _Float128 type
name is printed rather then the user specified long double type.  This
patch adds a new gdbarch method to allow PowerPC to detect the GCC
workaround.  The workaround checks for "_Float128" name when reading the
base typedef from the die_info.  If the workaround is detected, the type
and format fields from the _Float128 typedef are copied to the long
double typedef.  The same is done for the complex long double typedef.

This patch fixes 74 regression test failures in
gdb.base/whatis-ptype-typedefs.exp on PowerPC with IEEE float 128 as the
default on GCC.  It fixes one regression test failure in
gdb.base/complex-parts.exp.

The patch has been tested on Power 10 where GCC defaults to IEEE Float
128-bit and on Power 10 where GCC defaults to the IBM 128-bit float.  The
patch as also been tested on X86-64 with no new regression failures.

1 files changed, 19 insertions, 4 deletions

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 8f35b973f3e..29a95cb8b2f 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -14721,14 +14721,29 @@ static struct type *
 read_typedef (struct die_info *die, struct dwarf2_cu *cu)
 {
   struct objfile *objfile = cu->per_objfile->objfile;
-  const char *name = NULL;
-  struct type *this_type, *target_type;
+  const char *name = dwarf2_full_name (NULL, die, cu);
+  struct type *this_type;
+  struct gdbarch *gdbarch = objfile->arch ();
+  struct type *target_type = die_type (die, cu);
+
+  if (gdbarch_dwarf2_omit_typedef_p (gdbarch, target_type, cu->producer, name))
+    {
+      /* The long double is defined as a base type in C.  GCC creates a long
+	 double typedef with target-type _Float128 for the long double to
+	 identify it as the IEEE Float128 value.  This is a GCC hack since the
+	 DWARF doesn't distinquish between the IBM long double and IEEE
+	 128-bit float.	 Replace the GCC workaround for the long double
+	 typedef with the actual type information copied from the target-type
+	 with the correct long double base type name.  */
+      this_type = copy_type (target_type);
+      this_type->set_name (name);
+      set_die_type (die, this_type, cu);
+      return this_type;
+    }
 
-  name = dwarf2_full_name (NULL, die, cu);
   this_type = type_allocator (objfile).new_type (TYPE_CODE_TYPEDEF, 0, name);
   this_type->set_target_is_stub (true);
   set_die_type (die, this_type, cu);
-  target_type = die_type (die, cu);
   if (target_type != this_type)
     this_type->set_target_type (target_type);
   else