Re: Possible Issue in ieeefp.h

[Craig Howland <howland at LGSInnovations dot com>]

On 11/21/2016 11:38 AM, Joel Sherrill wrote:
> On 11/21/2016 10:26 AM, Craig Howland wrote:
> > On 11/21/2016 11:08 AM, Joel Sherrill wrote:
> > > Hi
> > >
> > > An RTEMS user has tried to build GNU FORTRAN. It used to build
> > > and test OK. I am copying his report and my suggestion. I think
> > > the constants tested in ieeefp.h do NOT match those predefined
> > > by GCC. I need someone more knowledgable to confirm.
> > >
> > > Thanks.
> > >
> > > --joel
> > >
> > > > On Mon, Nov 21, 2016 at 9:24 AM, Ricardo Derbes <rmderbes@gmail.com> wrote:
> > > > Hello.
> > > > I'm trying to build rtems toolchain for i386 using
> > > > rtems-source-builder with fortran support (--with-fortran option).
> > > > The RSB I'm using has been dowloaded from git, commit
> > > > 534332f22a66f16b4022e87ae50c11ff20c98dcb from Sep 12 2016.
> > > >
> > > > ...
> > > >
> > > > As for my application I need fortran support, how can I fix this problem?
> > > > As long I can see, all symbols that the compiler claims as undeclared
> > > > are indeed declared and accessible in file
> > > > ~/devel4.12-i386.fortran/rtems-source-builder/rtems/build/i386-rtems4.12-gcc-6-20160609-newlib-2.4.0.20160527-x86_64-linux-gnu-1/gcc-6-20160609/newlib/libc/include/ieeefp.h 
> > > >
> > > >
> > > > May be it's missing a symbol, e.g a proper value for LDBL_MANT_DIG ?
> > > >
> > > >
> > > > I see that GCC predefines these symbols:
> > > >
> > > > #define __FLT_MANT_DIG__ 24
> > > > #define __DEC64_MANT_DIG__ 16
> > > > #define __LDBL_MANT_DIG__ 53
> > > > #define __DBL_MANT_DIG__ 53
> > > > #define __DEC32_MANT_DIG__ 7
> > > > #define __DEC128_MANT_DIG__ 34
> > > >
> > > > And ieeefp.h in newlib has this:
> > > >
> > > > #elif LDBL_MANT_DIG == 53
> > > > /* This happens when doubles are 32-bits and long doubles are 64-bits.  */
> > > > #define EXT_EXPBITS     11
> > > > #define EXT_FRACHBITS   20
> > > > #define EXT_FRACLBITS   32
> > > > #define __ieee_ext_field_type unsigned long
> > > >
> > > > I am suspicious that the ifdef should use __LDBL_MANT_DIG__ not LDBL_MANT_DIG.
> > ieeefp.h is definitely intending to use LDBL_MANT_DIG.  This is the C-standard
> > defined name which is supposed to be defined in float.h, and which ieeefp.h
> > directly states it is relying on.  Apparently the float.h being used is not
> > properly defined/set up, and this is what needs to be corrected.
>
> I have never poked in this area before. Where is this generated?
> Help on where to look and what could be broken is appreciated.
>
> Thanks.
>
> > Craig
>
> --joel
float.h is generally assumed to be supplied by the compiler, in a fashion 
similar to stdarg.h, as it contains compiler-specific sizes.  (I just took a 
look at the GCC 4.1.1 PowerPC cross compiler's float.h, and they pretty much 
just turn their internal defines into the C-required names.)  Probably the 
--with-fortran option is messing things up.  Could you perhaps build without it 
just to get the right float.h, and then use that as a bootstrap of sorts to make 
the --with-fortran build work?  (Any way of finding the right float.h for your 
GCC version should work.)
Craig