Re: [patch] Fix thinko in powerpc default specs for -mabi

[Olivier Hainque <hainque@adacore.com>]

Hi Segher,

> On 3 Oct 2022, at 18:13, Segher Boessenkool <segher@kernel.crashing.org> wrote:
> 
> -mabi= does two separate things, unfortunately.
> 
> First, you can use it to set the base ABI: elfv1, elfv2.  But you can
> also use it to set ABI variants, ABI options: -mabi={no-,}altivec,
> -mabi={ieee,ibm}longdouble, -mabi=vec-{extabi,default}.  Things in that
> latter category are completely orthogonal to anything else (except that
> some only make sense together with some base ABIs).

Ooh, I see. I understood there were abi related options internally
(this is quite visible throughout the code of course) but didn't click
on all the implications on the command -mabi line interface.

> Base ABI is not selectable for most, it is implied by your target
> triple.  -mabi=elfv[12] only makes sense for targets that have either of
> the two by default.

Yes, I can see that now.

>> We have been using this for about a year now in gcc-11 based toolchains.
>> This helps our dejagnu testsuite runs for VxWorks on powerpc and 
>> hasn't produced any ill side effect to date.
> 
> So what exactly is this meant to do?

Biased by other ports, the presence of multiple -mabi switches
just seemed wrong on its own, so the first level motivation was
simply to address that. There might have been interactions with
another change in what we observed at the time.

I understand now that multiple -mabi on the command line is not
a problem per se, so:

> But it does not seem correct.  -mabi=optionA should not override the
> -mabi=optionB set in --with-abi=, where A and B are independent, nor
> should it override the base ABI.

Agreed!

Thanks a lot for your constructive feedback, much appreciated.

With Kind Regards,

Olivier