Re: [gentoo-dev] Re: [gentoo-commits] repo/gentoo:master commit in: media-libs/x265/

[Alexis Ballier]

On Mon, 2020-05-25 at 21:09 -0400, Mike Gilbert wrote:
> On Mon, May 25, 2020 at 7:35 PM Alexis Ballier <aballier@g.o>
> wrote:
> > On Mon, 2020-05-25 at 17:04 -0400, Mike Gilbert wrote:
> > > On Mon, May 25, 2020 at 3:18 PM Michał Górny <mgorny@g.o>
> > > wrote:
> > > > On Mon, 2020-05-25 at 19:49 +0200, Alexis Ballier wrote:
> > > > > On Mon, 25 May 2020 11:26:26 -0400
> > > > > Mike Gilbert <floppym@g.o> wrote:
> > > > >
> > > > > > On Mon, May 25, 2020 at 9:13 AM Alexis Ballier <
> > > > > > aballier@g.o>
> > > > > > wrote:
> > > > > > > On Sun, 24 May 2020 20:25:11 +0000 (UTC)
> > > > > > > "Thomas Deutschmann" <whissi@g.o> wrote:
> > > > > > >
> > > > > > > > commit:     6e149596cc76f1bbcee6720828c8c8c92420f2a3
> > > > > > > > Author:     Thomas Deutschmann <whissi <AT> gentoo
> > > > > > > > <DOT>
> > > > > > > > org>
> > > > > > > > AuthorDate: Sun May 24 19:47:08 2020 +0000
> > > > > > > > Commit:     Thomas Deutschmann <whissi <AT> gentoo
> > > > > > > > <DOT>
> > > > > > > > org>
> > > > > > > > CommitDate: Sun May 24 20:23:53 2020 +0000
> > > > > > > > URL:
> > > > > > > > https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=6e149596
> > > > > > > >
> > > > > > > > media-libs/x265: drop USE=pic
> > > > > > > >
> > > > > > > > Gentoo's toolchain uses PIC by default. Since USE=asm
> > > > > > > > was
> > > > > > > > added,
> > > > > > > > we no longer need a USE flag to control that behavior.
> > > > > > >
> > > > > > > You got it wrong here it seems: USE=pic does not control
> > > > > > > whether
> > > > > > > the toolchain produces PIC or not. Shared libs always
> > > > > > > are,
> > > > > > > and have
> > > > > > > always been, built that way on Gentoo.
> > > > > > > In this case, USE=pic means "no matter what it costs, I
> > > > > > > do
> > > > > > > not want
> > > > > > > textrels", for the cases of hand written assembly that
> > > > > > > has to
> > > > > > > be
> > > > > > > rewritten to support PIC. And, still in this case, this
> > > > > > > costs
> > > > > > > a lot
> > > > > > > of performance, so it is enabled by default on hardened
> > > > > > > profiles
> > > > > > > and not others.
> > > > > > > Textrels work fine (on some architectures), they disallow
> > > > > > > W^X
> > > > > > > and
> > > > > > > force each process using the shared lib to make a "copy"
> > > > > > > at
> > > > > > > runtime
> > > > > > > in order to resolve relocations, so are not desirable but
> > > > > > > sometimes
> > > > > > > the cost outweights the gain.
> > > > > > >
> > > > > > > Plus, profiles/features/hardened enables pic by default
> > > > > > > but
> > > > > > > knows
> > > > > > > nothing about USE=asm so this is a regression for them.
> > > > > >
> > > > > > The USE flag toggles use of assembly, not use of PIC. The
> > > > > > default USE
> > > > > > value in the hardened profile should not drive decisions on
> > > > > > what we
> > > > > > name USE flags.
> > > > >
> > > > > ... but using a global well documented useflag instead of a
> > > > > local
> > > > > invention should drive such decisions.
> > > >
> > > > What 'global well documented useflag'?
> > >
> > > It's neither global, nor well-documented, but several packages do
> > > define it locally.
> > >
> >
> > https://gitweb.gentoo.org/repo/gentoo/historical.git/commit/profiles/use.desc?id=103236c295aa30e5e42cfc8a7429e4eea5f0d680
> >
> > https://gitweb.gentoo.org/repo/gentoo/historical.git/commit/profiles/use.desc?id=784deb7134b9d430546557a8f8a0877bf35c02ba
> >
> > I guess this hasn't been really discussed back then.
> >
> > It is also used in a global way in profiles (make.defaults).
> >
> > > Personally, I think it should be renamed to "asm" or something
> > > similar
> > > in the majority of cases where it actually disables all use of
> > > assembly code.
> >
> > Thankfully these days there's usually no need to disable asm to
> > have
> > pic. hardened has no mention of that flag, and I think that e.g.
> > for
> > openssl they would have noticed long ago.
> > And again, 'asm' as a useflag makes no sense: if it works and
> > simply
> > replaces a C function by a faster one then it shouldn't even be an
> > useflag. 'pic' on the other hand conveys the tradeoff idea.
>
> If I understand you correctly, we should just drop the USE="pic"
> logic
> from the remaining packages that have it? Or are you trying to say
> something else?


Drop USE=asm unless there's a real reason to it: Such a useflag is,
IMHO, at the same level of a useflag on dev-lang/python that would
toggle dict's underlying implementations but not the semantics of the
language.
Have USE=pic for its historical meaning, aka, sacrificing everything to
have PIC shared libs because your system enforces this (pax).

Note that having the 'pic' useflag should be considered something to be
fixed: rewrite the asm in a PIC way. But these days nobody has the will
to do it since this is mostly an issue on x86+pax, both being slowly
decreasing.