[Buildroot] [PATCH] pkgconf: make wrapper relocatable

[Arnout Vandecappelle <arnout@mind.be>]

On 03/09/16 15:46, Peter Korsgaard wrote:
>>>>>> "Arnout" == Arnout Vandecappelle <arnout@mind.be> writes:
>
>   > On 03/09/16 15:31, Peter Korsgaard wrote:
>   >>>>>>> "Gustavo" == Gustavo Zacarias <gustavo@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.

  Read the section "Interpreter scripts" of execve(2). argv[0] is discarded.

>
> 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.

  So we need to readlink it first.

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

  For the hardlink case there is no solution.


  Regards,
  Arnout

-- 
Arnout Vandecappelle      arnout dot vandecappelle at essensium dot com
Senior Embedded Software Architect . . . . . . +32-478-010353 (mobile)
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