[RFC][PATCH] powerpc/64be: use ELFv2 ABI for big endian kernels

[Michael Ellerman]

Segher Boessenkool <segher at kernel.crashing.org> writes:

> On Fri, Nov 25, 2016 at 09:22:16AM +1100, Michael Ellerman wrote:
>> >> >> Question, are there any fundamental reasons we shouldn't use the ELFv2
>> >> >> ABI to build big endian kernels if the compiler supports it?
>> >> >
>> >> > No one uses ELFv2 for BE in production, and it isn't thoroughly tested
>> >> > at all, not even regularly tested.  "Not supported", as far as GCC is
>> >> > concerned (or any of the distros AFAIK).
>> >> 
>> >> Is this actually unsupported by gcc?
>> >
>> > It may or may not work.  We of course try to keep it working, or make
>> > it work if it doesn't now.  But it isn't regularly tested, and it isn't
>> > a target that is considered for the release criteria (see
>> > https://gcc.gnu.org/gcc-7/criteria.html -- powerpc64{,le}-linux, i.e.
>> > ABIv1 for BE, ABIv2 for LE).
>> 
>> It doesn't actually say that though. It just says
>> powerpc64-unknown-linux-gnu. So how is someone, say the musl folks,
>> supposed to know that BE ABIv2 is not supported?
>
> Because their target is powerpc64*-*-linux-musl instead?  It is not on
> the release criteria list, it is not something we make any claims about.
>
> How would you know -m32 -mlittle is not well tested at all?  It is in much
> the same boat: unusual combinations of options, and unusual configurations,
> are not well tested.  You have to build a separate C library just to get
> started with it, that should tell you there are some rough waters ahead!

Yeah OK, I guess that's the part that's confusing me.

Because we're hairy chested kernel programmers we don't actually build a
C library at all. So we don't get that hint that we're using an odd
combination, we just configure the toolchain, build it and off we go.

cheers