Re: [rfa] mips argument passing fixes for o32

[Daniel Jacobowitz <dmj+@andrew.cmu.edu>]

On Sun, Jul 15, 2001 at 05:50:16PM -0400, Andrew Cagney wrote:
> You wouldn't have access to such a machine by any chance? :-)
> 
> I'm getting the feeling I'm wrong with this one - for some strange 
> historical reason LE o32 really does left/right shift small parameters 
> (I'm still mining the archives).
> 
> Assuming that is the case ...
> 
> >  if (!MIPS_EABI
> >  		      && MIPS_SAVED_REGSIZE < 8
> > -		      && TARGET_BYTE_ORDER == BIG_ENDIAN
> > +		      && (TARGET_BYTE_ORDER == BIG_ENDIAN
> > +			  || TYPE_LENGTH (arg_type) < MIPS_SAVED_REGSIZE)
> >  		      && partial_len < MIPS_SAVED_REGSIZE
> >  		      && (typecode == TYPE_CODE_STRUCT ||
> >  			  typecode == TYPE_CODE_UNION))
> 
> I don't know that line being added should be
> 
> 	
> 
> || TYPE_LENGTH (arg_type) < MIPS_SAVED_REGSIZE
> 
> 
> it should at least be guarded by ``ABI == o32''.  What does LE n32 do 
> for instance?
> If GCC, for o32, always left shifts the structs dregs (PARTIAL_LEN < 
> MIPS_SAVED_REGSIZE) then is just the ABI test needed?

That's not what it does, though.  It only left-shifts the dregs if they
constitute the entire structure; thus the check I used.  Little-endian
will left-shift only small structs, while big-endian will left-shift
small structs or leftovers.

As for when it is done, GCC says:
      if (struct_p && int_size_in_bytes (type) < UNITS_PER_WORD
          && ! TARGET_64BIT && mips_abi != ABI_EABI)

However, there's a comment to the effect that the !TARGET_64BIT is
actually wrong, and being used only for efficiency.  So I'm not sure
precisely when this applies.  It seems that !MIPS_EABI and
MIPS_SAVED_REGSIZE < 8 would agree with at least the way that GCC does
things, but GCC is not a sterling example of n32 or n64 compatibility.

> PS: That function is the official example of how to _not_ multi-arch an ABI.

And does it ever show...

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer