[fortran] Disable use of -malign-double

[Joseph S. Myers]

On Wed, 31 Jan 2007, Jerry DeLisle wrote:

> I think we should have a test at compile time to determine if the libraries
> have been aligned and if not issue an error if -malign-double is used. I am
> not sure exactly how we would do this, but maybe add a simple structure and
> test function in the library that is called at compile time to answer the
> question.

An established approach for checking ABI compatibility is to tag object 
files and libraries with ABI information and then have the linker complain 
if linking together objects with incompatible ABIs.  Sometimes there is a 
standard for the object file tags (e.g. in the ARM EABI), but if there 
isn't one for x86 you could establish a convention followed by GCC and GNU 
binutils for marking whether objects use align-double.

GCC may end up needing such conventions more generally for LTO in order to 
tell whether it can optimize across two objects compiled with different 
options.

-- 
Joseph S. Myers
joseph@codesourcery.com