Re: Support for ARMv7, hardware math

Vaclav Mocek <little.owl@xxxxxxxx> · Sun, 28 Nov 2010 14:12:32 +0000



    On 11/28/2010 11:14 AM, Peter
      Robinson wrote:
      

        > From my interpretation of the gcc notes on float it looks
        like the two
        

        are mutually exclusive. From the notes "Note that the hard-float
        and
        

        soft-float ABIs are not link-compatible; you must compile your
        entire
        

        program with the same ABI, and link with a compatible set of
        

        libraries. "
        

      The reason is entirely different calling convention. With hardware
      floating point linkage, arguments and return values are passed in
      VFP registers; you have to be sure that target contain VFP. With
      software floating point linkage arguments and return values are
      passed in ARM registers; it is slower - data has to be transferred
      to VFP.
      

      My
        understanding is that all the ARMv7 chips have vfp3 but there's
        two
        

        different versions (16 and 32) which means that all the A8 chips
        

        should support that, and it seems on the A9 its optional.
        

      Choice of vfp3-16 is the best option right now, otherwise the
      number of possible targets would be limited.
      

      I vote for vfp3-16 + hardfp + separate repository ;-)
      

      Vaclav
      

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