[Buildroot] [PATCH] pkgconf: make wrapper relocatable

[Peter Korsgaard]

>>>>> "Arnout" == Arnout Vandecappelle <arnout at mind.be> writes:

 > On 03/09/16 15:31, Peter Korsgaard wrote:
 >>>>>>> "Gustavo" == Gustavo Zacarias <gustavo at zacarias.com.ar> writes:
 >> 
 >> > On 09/03/16 11:00, Peter Korsgaard wrote:
 >> >> Well, we cannot really break existing features to add new ones. The
 >> >> relative location between the pkg-config wrapper script and the staging
 >> >> directory is constant (or rather known at build time), so I guess we can
 >> >> do something with /proc/self/exe. We might need to implement the wrapper
 >> >> in C instead for that to work as /proc/self/exe for a shell script seems
 >> >> to return /bin/dash here.
 >> 
 >> > That's overly complicated for no value at all.
 >> > You know the sysroot is in the host directory as well, so you just
 >> > need to filter out /usr/bin from $0 and hardcode the tuple in the
 >> > wrapper -
 >> > that's guaranteed to not change, otherwise you're in serious trouble.
 >> 
 >> Yes, that's basically what I'm saying +/- the question if you want to
 >> rely on $0 containing the full path to the wrapper or if you use
 >> /proc/self/exe instead.

 >  $0 will always contain the full relative path to the wrapper, no?
 > Even if it was found through PATH, the PATH search is done by libc so
 > the shell will be invoked with the full (absolute or relative) path to
 > the wrapper and use that as $0. Or am I missing something?

well, if executed throyh a shell it will - But if I write code to call
execve I get to chose what argv[0] should be.

Some software (like upx) wants to handle situations like this, but it
might not be necessary for our pkg-config / vala wrappers.

>  I think the /proc/self/exe thing was something to deal with symlinks,
 > which isn't the issue here.

That's another reason. If somebody does a symlink to our wrapper, then
$0 will contain the full path to the link, not to the wrapper
itself.

If somebody does a hardlink, /proc/self/exe won't even fix it for you -
But that is probably quite unlikely.

-- 
Venlig hilsen,
Peter Korsgaard