Re: [gentoo-dev] [PATCH] systemd.eclass: remove SYSROOT from pkg-config output

[Mike Gilbert]

On Sun, Jan 3, 2021 at 7:52 AM James Le Cuirot <chewi@g.o> wrote:
>
> On Sat,  2 Jan 2021 20:09:04 -0500
> Mike Gilbert <floppym@g.o> wrote:
>
> > When cross-compiling, users will typically have
> > PKG_CONFIG_SYSROOT=${SYSROOT} defined via pkg-config wrapper.
> >
> > When PKG_CONFIG_SYSROOT is set, all paths included in pkg-config
> > output get prefixed with this value.
> >
> > Signed-off-by: Mike Gilbert <floppym@g.o>
> > ---
> >
> > This patch has already been pushed, but I figured I would send it for
> > review in case someone else can think of a failure case, or has a better
> > solution.
> >
> >  eclass/systemd.eclass | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/eclass/systemd.eclass b/eclass/systemd.eclass
> > index 81065a0af79a..f6d1fa2d92d6 100644
> > --- a/eclass/systemd.eclass
> > +++ b/eclass/systemd.eclass
> > @@ -50,6 +50,7 @@ _systemd_get_dir() {
> >
> >       if $(tc-getPKG_CONFIG) --exists systemd; then
> >               d=$($(tc-getPKG_CONFIG) --variable="${variable}" systemd) || die
> > +             d=${d#${SYSROOT}}
> >               d=${d#${EPREFIX}}
> >       else
> >               d=${fallback}
>
> I was going to say this is not the best approach as it would be better
> to tell pkg-config to not add the SYSROOT in the first place. I now
> realise we have shot ourselves in the foot with cross-pkg-config as it
> uses SYSROOT to set both PKG_CONFIG_SYSROOT_DIR to control the output
> and PKG_CONFIG_LIBDIR to find the .pc files in the first place. I have
> had prefix-related fixes for cross-pkg-config lined up for over a year
> but unfortunately they do not address this. Trying to accommodate this
> use case would probably just make it more confusing though so maybe
> your approach is best after all.

It would be cleaner overall if we could prevent SYSROOT from being
added to the paths in the first place.

> The EPREFIX line is (sometimes) wrong in EAPI 7 though and the same goes
> for udev.eclass. It took a while to get this agreed and corrected in
> PMS but if SYSROOT points to / then the effective prefix is BROOT, not
> EPREFIX; they may not be the same.

Ugh, that "corrected" logic in PMS head is nasty.

> If you just strip ESYSROOT then
> it will always do the right thing but you'll need this fall back for
> older EAPIs. I'm not sure why you didn't do it in one line?

I was trying to accommodate older EAPIs that do not define ESYSROOT.
This seemed like the simplest approach. It also allows for the case
where someone is not using cross-pkg-config, and
PKG_CONFIG_SYSROOT_DIR is unset. Since SYSROOT and EPREFIX are removed
separately, if one of them is already missing, it will just be
skipped.

> I forget if EPREFIX is normalised to be / rather thank blank.
>
> d=${d#${SYSROOT%/}/${EPREFIX#/}}

SYSROOT never ends with a / in modern versions of portage (regardless
of EAPI), so there's currently no need to remove a trailing slash.

https://gitweb.gentoo.org/proj/portage.git/commit/?id=1b5110557d1dd725f7c12bbed4b7ceaaec29f2a3

I have never seen EPREFIX equal to "/", or end with a trailing slash.
Given it is most commonly used as "${EPREFIX}/usr", this would result
in double-slashes everywhere.