Re: gfortran and -mlong-double-128

[Paul Brook <paul@codesourcery.com>]

On Thursday 16 February 2006 11:09, François-Xavier Coudert wrote:
> Hi all,
>
> I'm sending this mail because I'm a bit confused about the
> -mlong-double-128 option on (for example) ppc64-linux, and its impact
> on gfortran/libgfortran.
>
> When I simply bootstrap a compiler with "configure
> --with-cpu=default32", I get a gfortran that does only have kind=4 and
> kind=8 reals (corresponding to C types float and double) by default.
> When I use this gfortran with the -mlong-double-128 option, the
> real(kind=16) floating point type is accepted at compile-time, but the
> I/O library in libgfortran doesn't know how to deal with it (since,
> when libgfortran was compiled, it did not detect that real(kind=16)
> was available), and the code fails at runtime.
>
> What should we do about that? I see a few options:
>   1. refuse -mlong-double-128 for Fortran code; easiest, but not
> exactly satisfying
>   2. build multiple instances of the library, as is currently done for
> the -m32/-m64 options
>   3. build only one instance of the library, but build it with
> -mlong-double-128 enabled, since as far as libgfortran is concerned,
> it only adds a new floating-point type.

IMHO libgfortran shouldn't have to know or care about this option at all.
If you want a long-double-128 toolchain, then toplevel configure should be 
passing that option when configuring target libraries.

Having gfortran magically know about certain ABI breaking options, and doing 
funny things on certain targets seems a very bad precedent to me.

Paul