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

[Richard Sandiford <rsandifo@nildram.co.uk>]

Paul Koning <pkoning@equallogic.com> writes:
>>>>>> "Richard" == Richard Sandiford <rsandifo@nildram.co.uk> writes:
>
>  Richard> I agree with Joseph here.  Although it's redundant to
>  Richard> specify -mfp64 with -msoft-float, it isn't actively wrong.
>  Richard> The options have traditionally been orthogonal.  I don't
>  Richard> think the assembler should assume that -mfp64 implies
>  Richard> -mhard-float.
>
> It seems strange, since -msoft-float means no float registers, while
> -mfp64 says there are float registers and they are 64 bits wide.

Well, -mhard-float and -msoft-float are ABI options.  -mfp64 is
an architectural configuration option, and only affects calling
conventions when combined with -mhard-float.  It is perfectly
possible to write code that conforms to the soft-float ABI while
still using FPU instructions within a function.  (Strictly speaking,
the use of FPU instructions is also part of the ABI.  But it isn't
what this attribute specifies; this attribute is about the calling
conventions.)

The practical example of the difference is MIPS16.  -mhard-float
-mips16 doesn't say "use the FPU from MIPS16 code"; you can't.
It says instead that the hard-float ABI is in effect, and that
we need to use special stubs to interface with non-MIPS16 code.

Richard