Re: [PATCH] MIPS: Add a GNU attribute for -mips32 -mfp64 objects

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Thu, 15 Nov 2007, Thiemo Seufer wrote:

> The -mfp64 is passed, but it is AFAICS unlikely to generate invalid
> tagging: Presumably the reason to use the compiler's -mfp64 option is
> to generate 64-bit FP code, which isn't compatible to the other variants
> as soon as e.g. a mfhc1 instruction is used.

This tagging in the assembler would need of course to be conditioned on 
generating O32 code, since as I understand it -mfp64 only selects a novel 
ABI variant for O32, N32 and N64 are covered by the normal hard-float ABI 
setting.

> The idea is to pass the relevent options to the assembler (at least for
> .s/.S source files, for compiler generated files it would be redundant).

Indeed - for compiler generated files, if you need to modify the compiler 
to pass down the option, you may as well modify it to set the attribute 
itself.

> A hard-float object which happens not to use floating point at all wouldn't
> be link compatible any more, this is the same effect which was evidently
> regarded as acceptable in newer GCC compilers.

Acceptable but not ideal; we'd hope in future to make GCC detect whether 
the particular source file is or is not affected, and then set the 
attribute saying it's unaffected if it's unaffected.  I suppose unaffected 
assembler files can always explicitly set the attribute to say so.

-- 
Joseph S. Myers
joseph@codesourcery.com