On Sat,  2 Jan 2021 20:09:04 -0500
Mike Gilbert <floppym@gentoo.org> 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@gentoo.org>
> ---
> 
> 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.

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. 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 forget if
EPREFIX is normalised to be / rather thank blank.

d=${d#${SYSROOT%/}/${EPREFIX#/}}

-- 
James Le Cuirot (chewi)
Gentoo Linux Developer