Re: [PATCH] Fix float to LONGEST conversion.

["Ali Tamur via gdb-patches" <gdb-patches at sourceware dot org>]

Hi,
If there are no other concerns I am going to submit this tomorrow morning.
Thanks.

On Sun, Sep 8, 2019 at 7:36 PM Ali Tamur <tamur@google.com> wrote:
>
> Hi,
> Can I submit if there aren't any other concerns?
> Thanks,
> Ali
>
> On Wed, Sep 4, 2019 at 2:28 PM Ali Tamur <tamur@google.com> wrote:
> >
> > Updated the commit message:
> > >
> >     Fix float to LONGEST conversion.
> >
> >     The code used to have undefined behaviour when template parameter is float and
> >     host_float is NaN, because it attempted to convert NaN value to LONGEST at the
> >     last statement. This frequently caused crashes on tests that checked "info
> >     all-registers" (at least when the code is compiled with clang; I didn't test
> >     with gdb).
> >
> > On Wed, Aug 28, 2019 at 1:29 AM Andrew Burgess <andrew.burgess@embecosm.com> wrote:
> >>
> >> * Ali Tamur via gdb-patches <gdb-patches@sourceware.org> [2019-08-27 20:28:08 -0700]:
> >>
> >> > The code used to have undefined behaviour.
> >>
> >> I would much prefer to see a more detailed explanation for _why_ the
> >> previous behaviour is undefined.  I ran my eye over the old code but
> >> didn't see anything obvious.
> >>
> >> If at a later date I come back and want to figure out why this patch
> >> went in it would be nice if the commit message could tell me
> >> everything I need to know.
> >>
> >> Thanks,
> >> Andrew
> >>
> >>
> >>
> >> >
> >> >
> >> > gdb/ChangeLog:
> >> >       *gdb/target-float.c (host_float_ops<T>::to_longest): Update
> >> >       implementation.
> >> > ---
> >> >  gdb/target-float.c | 17 +++++++++++------
> >> >  1 file changed, 11 insertions(+), 6 deletions(-)
> >> >
> >> > diff --git a/gdb/target-float.c b/gdb/target-float.c
> >> > index 39abb12696..0fd71c0dc3 100644
> >> > --- a/gdb/target-float.c
> >> > +++ b/gdb/target-float.c
> >> > @@ -1007,13 +1007,18 @@ host_float_ops<T>::to_longest (const gdb_byte *addr,
> >> >  {
> >> >    T host_float;
> >> >    from_target (type, addr, &host_float);
> >> > -  /* Converting an out-of-range value is undefined behavior in C, but we
> >> > -     prefer to return a defined value here.  */
> >> > -  if (host_float > std::numeric_limits<LONGEST>::max())
> >> > -    return std::numeric_limits<LONGEST>::max();
> >> > -  if (host_float < std::numeric_limits<LONGEST>::min())
> >> > +  T min_possible_range = static_cast<T>(std::numeric_limits<LONGEST>::min());
> >> > +  T max_possible_range = -min_possible_range;
> >> > +  /* host_float can be converted to an integer as long as it's in
> >> > +     the range [min_possible_range, max_possible_range). If not, it is either
> >> > +     too large, or too small, or is NaN; in this case return the maximum or
> >> > +     minimum possible value.  */
> >> > +  if (host_float < max_possible_range && host_float >= min_possible_range)
> >> > +    return static_cast<LONGEST> (host_float);
> >> > +  if (host_float < min_possible_range)
> >> >      return std::numeric_limits<LONGEST>::min();
> >> > -  return (LONGEST) host_float;
> >> > +  /* This line will be executed if host_float is NaN.  */
> >> > +  return std::numeric_limits<LONGEST>::max();
> >> >  }
> >> >
> >> >  /* Convert signed integer VAL to a target floating-number of type TYPE
> >> > --
> >> > 2.23.0.187.g17f5b7556c-goog
> >> >