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Message-ID: <2956705.fEcJ0Lxnt5@sheen>
Date: Sun, 31 May 2020 00:57:12 +0000
From: Will Springer <skirmisher@...tonmail.com>
To: Segher Boessenkool <segher@...nel.crashing.org>, linuxppc-dev@...ts.ozlabs.org
Cc: libc-alpha@...rceware.org, eery@...erfox.es, daniel@...aforge.org, musl@...ts.openwall.com, binutils@...rceware.org, libc-dev@...ts.llvm.org
Subject: Re: ppc64le and 32-bit LE userland compatibility
On Saturday, May 30, 2020 12:22:12 PM PDT Segher Boessenkool wrote:
> The original sysv PowerPC supplement
> http://refspecs.linux-foundation.org/elf/elfspec_ppc.pdf
> supports LE as well, and most powerpcle ports use that. But, the
> big-endian Linux ABI differs in quite a few places, and it of course
> makes a lot better sense if powerpcle-linux follows that.
Right, I should have clarified I was talking about Linux ABIs
specifically.
> What patches did you need? I regularly build >30 cross compilers (on
> both BE and LE hosts; I haven't used 32-bit hosts for a long time, but
> in the past those worked fine as well). I also cross-built
> powerpcle-linux-gcc quite a few times (from powerpc64le, from powerpc64,
> from various x86).
There was just an assumption that LE == powerpc64le in libgo, spotted by
q66 (daniel@ on the CC). I just pushed the patch to [1].
> Almost no project that used 32-bit PowerPC in LE mode has sent patches
> to the upstreams.
Right, but I have heard concerns from at least one person familiar with
the ppc kernel about breaking existing users of this arch-endianness
combo, if any. It seems likely that none of those use upstream, though ^^;
> The ABI says long longs are passed in the same order in registers as it
> would be in memory; so the high part and the low part are swapped
> between BE and LE. Which registers make up a pair is exactly the same
> between the two. (You can verify this with an existing powerpcle-*
> compiler, too; I did, and we implement it correctly as far as I can
> see).
I'll give it a closer look. This is my first time poking at this sort of
thing in depth, so excuse my unfamiliarity!
> A huge factor in having good GCC support for powerpcle-linux (or
> anything else) is someone needs to regularly test it, and share test
> results with us (via gcc-testresults@). Hint hint hint :-)
>
> That way we know it is in good shape, know when we are regressing it,
> know there is interest in it.
Once I have more of a bootstrapped userland than a barely-functional
cross chroot, I'll get back to you on that :)
> gl;hf,
>
>
> Segher
Thanks,
Will [she/her]
[1]: https://github.com/Skirmisher/void-packages/blob/master/srcpkgs/gcc/patches/libgo-ppcle.patch
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