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On 31/03/14 06:16 PM, Michał Górny wrote:
> Hello, all.
>
> The late multilib ppc issues made me re-check our stable masks on
> abi_x86_* flags and, honestly, I'm not sure if we're doing things
> the right way. First, a quick summary.
>
>
> Let's consider dev-libs/elfutils that has a dependency on
> app-arch/bzip2. If we're building 32-bit elfutils, it needs 32-bit
> libbz2. This is enforced through a dep in form of:
>
> app-arch/bzip2[${MULTILIB_USEDEP}]
>
> that gets expanded into:
>
> app-arch/bzip2[abi_x86_32(-)?,abi_x86_64(-)?,...,abi_mips_o32(-)?,...]
>
> which means that any of the ABI_* flags that gets enabled on
> elfutils, needs to be enabled on bzip2 as well. Of course, some of
> use.forcing and masking gets applied here but that doesn't really
> matter.
>
>
> Now, since we're pretty much converting a lot of different
> packages, some of them are eligible for stabilization earlier than
> the others. However, the extra MULTILIB_USEDEPs enforce stabilizing
> multilib dependencies before the actual packages which made a few
> developers unhappy.
>
> That's why we decided to stable-mask the flags on affected
> packages. Since the flags are masked on stable, people can
> stabilize packages independently of whether their converted deps
> are stable or not. We will be worrying about that consistency once
> we decide to unmask the flags.
>
> The extra advantage of that is that we can avoid pushing stable
> users into the mess involved with partial conversion of emul-linux.
> The idea is pretty simple: we keep emul-linux for stable, and once
> everything is ready, we stable-unmask the flags and let stable
> users grok multilib.
>
>
> Now, to the problem. Currently we're just stable-masking
> abi_x86_32 on amd64. This serves the latter purpose well and seems
> to work for the former. This is probably because the remaining flag
> is use.forced (abi_x86_64 on amd64, and abi_x86_32 on x86) which
> seems to add it to implicit IUSE somehow.
>
> floppym has done some research w/ stable elfutils and no stable
> converted bzip2. It seems that if abi_x86_32 is stable.use.masked
> and abi_x86_64 is use.forced, repoman groks it. However, if we
> remove abi_x86_64 from use.force, it properly reports flag mismatch
> error (since no stable bzip2 has IUSE=abi_x86_64).
>
> Now, I honestly have no idea if this implicit use.force behavior
> is PMS-y or not, and how other PMs handle it. I can't find
> something like this in the PMS but that doc is horribly hard to
> cross-reference, so I might be missing something. I'd appreciate if
> someone could help me with that.
>
>
> That said, I have an alternate idea inspired by the ppc breakage.
> I'm thinking of replacing the amd64 abi_x86_32 mask with a global
> stable mask of all abi_*_* flags on the relevant packages.
>
> Differences:
>
> 1) old solution: native flag is forced, other flags are masked. new
> solution: all flags are masked.
>
> 2) old solution: we need to replicate the masks properly for
> different arches/profiles. new solution: we can keep a single mask
> for all arches.
>
> 3) old solution: MULTILIB_USEDEP magically works (w/ portage at
> least). new solution: since all flags are disabled,
> MULTILIB_USEDEP is a no-op and old packages match correctly.
>
> 4) old solution: forced native flag runs the native build. new
> solution: fallback code runs the native build (since no flags are
> enabled).
>
>
> Your thoughts?
>
... how messy is this going to be on current systems, if implemented?
This -is- going to cause use flag changes on a whackload of packages,
which at minimum I expect means a bunch of needless rebuilds.
I think it's probably best to keep with the current path, and just
hurry up the migration on x86. If we switch to masking all abi_*_*'s,
then not only do we rebuild a whackload of packages now, but we also
end up rebuilding them again when we remove the abi_*_* mask, -even
if- the alternative abi's aren't needed.
A note on #3: if MULTILIB_USEDEP -isnt- working on other PMs, i hope
we have bug reports and we should work to resolve those ASAP or
abandon the project/find a different solution. We're over a year into
it though (i think?) so i expect it's fine since I don't remember
hearing of any issues yet...
on a side note, to follow up -- when we do remove the masks, what're
the thoughts on perhaps changing the multilib profile on amd64 to
auto-enable abi_x86_32 flags on some packages? Indeed, if the
toolchain is converted to multilib-build, would this be enough to
differentiate between amd64-multilib and pure64? (bootstrapping may
of course still be a problem if users are trying to switch, but
probably not any more of a problem than it is right now, right?)
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