Re: [gentoo-dev] Monthly mips@ project status for April 2018

[Joshua Kinard]

On 4/2/2018 4:32 PM, Michał Górny wrote:
> W dniu pon, 02.04.2018 o godzinie 13∶27 -0400, użytkownik Joshua Kinard
> napisał:
>> On 4/2/2018 5:41 AM, Michał Górny wrote:
>>> W dniu nie, 01.04.2018 o godzinie 20∶40 -0700, użytkownik Matt Turner
>>> napisał:
>>>
>>>> My plan is to add stable 17.0 mips profiles when the keywording is
>>>> sorted out and kill two birds with one stone.
>>>
>>> Does it involve fixing the CHOST inconsistency so that we can finally
>>> get LLVM keyworded?
>>
>> Bug #515694, right?  Based on a very quick re-read, there are two
>> issues/blockers here:
>>
>> 1) Current Gentoo/MIPS support was originally based on gcc, thus, we've used
>> CHOST tuples that are recognized by gcc.
>
> As far as I'm aware GCC doesn't really care about which triplet is used.
> It's all controlled by --with-abi= option (I may have mistyped its
> name).

gcc might not, but odds are incredibly likely other software will.  I want to
say memory reminds me that glibc may be a culprit here, and may explain the
reason why someone redesigned the triplets/tuples in the first place.  E.g., I
*think* (but can't corroborate) that the "mips64-unknown-linux-gnuabin32" tuple
derived from glibc wanting to determine n32 support from the CHOST.  Again,
though, there are no known equivalents of this for uclibc-ng or musl targets
that I know of.


>> 2) clang lacks a CHOST tuple that defaults to n32.  n32 is the "ideal" ABI for
>> a 64-bit platform that doesn't need full 64bit (n64) binary support.
>>
>> As far as I can tell, we need to fix #2 before we can do anything about #1.
>> Once clang has a discrete CHOST tuple for n32, that'll put it on parity with
>> gcc, which itself appears to have a batch of more specific tuples to select
>> different ABIs.  You might want to just push upstream any patches you have that
>> adds this support first.
>
> It's chicken-egg problem. Before I can submit a patch upstream, I need
> someone with MIPS hardware and a proper profile (using disjoint,
> consistent triplets) to test it. Not to mention Gentoo needs to decide
> on the triplet in the first place.

Is there an option to cross-compile clang/llvm using a CHOST added by your
patch?  That should at least validate that the CHOST logic works out.  Any one
of us could then test out a statically-linked binary generated from such a
toolchain, assuming the target output matches one of our machines.

As far as Gentoo "deciding", I have to argue that it's not an "our fault" thing
or such.  Back when the port was started in ~2003, there was no such thing as
clang/llvm, so we used what CHOSTs gcc was happy with.  Life continued on from
there, with a few hiccups along the way.

I know of no authority that sets/decides what CHOSTs are valid and what aren't.
 That'd probably be a nice thing to have, TBH, as my irritation with FreeBSD's
versioned CHOSTs makes updating a Gentoo/FreeBSD userland mildly annoying.
That said, I don't have much of a problem adopting the Debian versions[1].  We
would just need a way to migrate existing installs, preferably w/o having to
recompile everything...

1. https://wiki.debian.org/Multiarch/Tuples

-- 
Joshua Kinard
Gentoo/MIPS
kumba@g.o
6144R/F5C6C943 2015-04-27
177C 1972 1FB8 F254 BAD0 3E72 5C63 F4E3 F5C6 C943

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