Re: [PATCHv2] gdb/fortran: Use floatformats_ia64_quad for fortran 16-byte floats

[Andrew Burgess <andrew.burgess@embecosm.com>]

* Tom Tromey <tromey@adacore.com> [2019-05-21 16:18:18 -0400]:

> >>>>> "Andrew" == Andrew Burgess <andrew.burgess@embecosm.com> writes:
> 
> Andrew> Would you like me to push a fix, or do you want to do it?
> 
> Go for it.

I pushed the below.

Thanks,
Andrew

---

commit dc42e902cc54af2b7e7b54a1171d562f867342d5
Author: Andrew Burgess <andrew.burgess@embecosm.com>
Date:   Tue May 21 22:14:05 2019 +0100

    gdb/fortran: Handle gdbarch_floatformat_for_type returning nullptr
    
    In this commit:
    
      commit 34d11c682fd96c7dbe3ebd6cd9033e65d51ec7a3
      Date:   Fri May 3 15:23:55 2019 +0100
    
          gdb/fortran: Use floatformats_ia64_quad for fortran 16-byte floats
    
    GDB was changed such that the Fortran's 16-byte float format was
    obtained by calling gdbarch_floatformat_for_type instead of just using
    gdbarch_long_double_format as it was before.
    
    The problem with this default_floatformat_for_type can return NULL in
    some cases, and the code introduced in 34d11c682f didn't consider
    this.
    
    This commit introduces several alternative strategies for finding a
    suitable 16-byte floating point type.  First GDB calls
    gdbarch_floatformat_for_type (this was what 34d11c682f added), if this
    returns null GDB will use gdbarch_long_double_format if it is the
    correct size (this was the format used before 34d11c682f).  Finally,
    if neither of the above provides a suitable type then GDB will create
    a new dummy type.
    
    This final dummy type is unlikely to provide an correct debug
    experience as far as examining the 16-byte floats, but it should
    prevent GDB crashing.
    
    gdb/ChangeLog:
    
            PR gdb/18644:
            * f-lang.c (build_fortran_types): Handle the case where
            gdbarch_floatformat_for_type returns a nullptr.

diff --git a/gdb/f-lang.c b/gdb/f-lang.c
index 5855c68b38c..e612eeda7f7 100644
--- a/gdb/f-lang.c
+++ b/gdb/f-lang.c
@@ -728,8 +728,16 @@ build_fortran_types (struct gdbarch *gdbarch)
     = arch_float_type (gdbarch, gdbarch_double_bit (gdbarch),
 		       "real*8", gdbarch_double_format (gdbarch));
   auto fmt = gdbarch_floatformat_for_type (gdbarch, "real(kind=16)", 128);
-  builtin_f_type->builtin_real_s16
-    = arch_float_type (gdbarch, 128, "real*16", fmt);
+  if (fmt != nullptr)
+    builtin_f_type->builtin_real_s16
+      = arch_float_type (gdbarch, 128, "real*16", fmt);
+  else if (gdbarch_long_double_bit (gdbarch) == 128)
+    builtin_f_type->builtin_real_s16
+      = arch_float_type (gdbarch, gdbarch_long_double_bit (gdbarch),
+			 "real*16", gdbarch_long_double_format (gdbarch));
+  else
+    builtin_f_type->builtin_real_s16
+      = arch_type (gdbarch, TYPE_CODE_ERROR, 128, "real*16");
 
   builtin_f_type->builtin_complex_s8
     = arch_complex_type (gdbarch, "complex*8",