Re: RFC & patch: Rework MIPS command-line handling

["Maciej W. Rozycki" <macro at ds2 dot pg dot gda dot pl>]

On 15 Jul 2002, Richard Sandiford wrote:

> It might also be nice to have a --with-abi configure option,
> although that's something we could add later...

 I'm not sure that is desireable -- I think the default ABI would best be
selectable with the target triple.  Like with "mips64abin32-*-*" or so.

> The reason for -mgp32 is for consitency with EABIs.  If you
> have a 32-bit EABI configuration like mipstx39-elf, does
> -mips4 select 64-bit EABI code, or 32-bit EABI code?  The
> first seems most natural to me, so the rule was: if you
> select a 64-bit processor, you get 64-bit code, unless
> you also select -mgp32.

 The implicit dependencies seem unfortunate for me.

> In general, the main reason to keep the implicit ABI selection
> is that that's what we've done before.  I didn't think there'd
> be much support for dropping it entirely.

 Certainly we can't drop them immediately, if there is no alternative,
which seem to be true from what you wrote above.  At least a single
release with both ways available must be created.

> The main difficulty with dropping the ABI selection entirely
> is: how do you select between the 32-bit and 64-bit versions
> of the EABIs?  mipstx39-elf-gcc generates 32-bit EABI code
> by default.  What happens if you select a 64-bit processor?
> Options I can see:
> 
> 1. Stick with the idea in the patch I sent.  Selecting a 64-bit
>    processor would usually select the 64-bit EABI, but adding
>    -mgp32 forces the 32-bit version.
> 
> 2. Reverse of (1).  You get the 32-bit version of the EABI
>    unless you use -mgp64.
> 
> 3. Add eabi32, eabi64, meabi32 and meabi64 to -mabi.  You get
>    the 32-bit version unless you use -mabi=eabi64.

 The last option seems the cleanest to me.  With your changes, it would
permit selecting a default ABI when configuring for certain embedded
targets as well (though I'm not sure how useful it would be in practice at
the moment, since I am not an embedded user).

  Maciej

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +