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

Andrew Burgess
2019-05-21T22:56:10Z

* 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");