Bug#875921: perl: Perl cross-build does not search correct paths for errno.h

[Wookey]

On 2017-09-16 11:16 +0300, Niko Tyni wrote:
> On Sat, Sep 16, 2017 at 01:06:48AM +0100, Wookey wrote:
> > Package: perl
> > Version: 5.24.1-3+deb9u1
> > Severity: normal
> > Tags: upstream patch
> 
> > There is no obvious variable in the config file to set up this
> > search. The closest is incpth, and using that does work, which is what
> > the attached patch does. I'm not sure that it is really the optimum
> > include path set to search. Possibly yet another config option for
> > this would be the right thing to do. Better would be defining one for
> > $DEB_HOST_MULTIARCH so the path can be composed. 
> 
> Hi, incpth is set in Configure based on what the preprocessor reports
> as its search path. Using that seems quite correct and robust to me.

OK. That seems fair enough. We can't really argue with our own cpp
search path, I guess :-) I admit that I'm not exactly sure of the
effect of the internal compiler paths in practice, but I presume they
are sensible and/or harmless in this case.
 
> Getting this upstream so that incpth is searched before the sysroot
> prefixed dirs (which degrade to normal /usr/include and /usr/local/include
> for us as sysroot is empty) may be hard. The sysroot stuff was added in
>  https://perl5.git.perl.org/perl.git/commitdiff/98b12e44bdf730698c03a5a4d8fc93c41d931637
> and is presumably still used by other cross compiling efforts.
> 
> Possibly the logic that could go upstream would be
> 
> 1) look in $sysroot/usr/{,local/}include but only if $sysroot is set
> 2) look in incpth
> 3) look in locincpth
> 4) if all fails, try /usr/include and /usr/local/include last

That seems sensible, but IMHO sysroot ought to work with a multiarch layout
too. One's sysroot filesystem could be a debian/ubuntu-based
one. Whilst we provide a 'better' mechanism for being able to cross
without having to use sysroots, sysroot-style building could still be
used.

The idea of sysroot is that the system works the same but the search
is moved down to a new root, not that it's a 'special' layout.

How about just decomposing incpth and prefixing all the paths with
$sysroot. That'll work for both multiarch and non-multiarch layout
both with and without sysroot. (unless people contrive to have
building environments where incpth is not set to anything sensible?)
If someone can justify adding $sysroot/usr/local/include even though
it's not in incpth on the end then do that too. Using $locincpth
sounds like it might be more correct here, but I'm not sure exactly
how that is intended to be used.

ie look in:
1) $sysroot/incpth
2) $sysroot/locincpth
maybe fall back to /usr/include and /usr/local/include but that's going beyond what the current code does.

That seems a cleaner solution to me.

Wookey
-- 
Principal hats:  Linaro, Debian, Wookware, ARM
http://wookware.org/
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