libbsd: Manipulating object files using waf build system

[Gedare Bloom]

On Tue, Aug 2, 2016 at 2:04 AM, Christian Mauderer
<christian.mauderer at embedded-brains.de> wrote:
> Hello,
>
> I have a second waf problem beneath the one already discussed in the
> other thread: Is it possible to do some object file manipulation before
> linking? To be exact I would need to rename some of the sections in the
> object files.
>
This might be one for a waf expert. I would try something like how IDL
files are twice-processed
https://waf.io/book/#_mixing_extensions_and_c_c_features

We had to do something like that to get the FilesystemImage generated,
e.g. examples-v2.git/filesystem/fat_ramdisk/wscript.

But I don't know if this is applicable to object files, since those
have to be created first. You might be able to define a custom task to
deal with .o files, or define a custom "link_task".

>
> If you want to stop reading, you can do it here. The following is only
> some background Information why this is necessary:
>
> Currently I'm porting the user space tool pfctl to set up the firewall
> pf to libbsd. For all initialized (zero or value) global or static
> variables I basically use the following method:
>
> - put all variables into one named linker section
> - save the section before calling the main
> - restore the section after calling main
>
> I'll add a more detailed description for the method that I used to port
> into the libbsd.txt as soon as I'm finished with the work.
>
>
> I have made some changes that I was trying to upstream to FreeBSD. The
> changes are quite similar to the ones for other programs:
>
> - Make const what can be const.
> - Make global variables static if possible.
> - Move some static variables out of function scope.
>
> I've suggested these changes on the FreeBSD mailing list here:
>
> https://lists.freebsd.org/pipermail/freebsd-hackers/2016-July/049772.html
>
> The last one (moving the static variables out of the functions) was
> necessary so I could easily add an attribute to the variables. Due to
> the fact that it is not really an improvement, it has started some
> discussion:
>
> https://lists.freebsd.org/pipermail/freebsd-hackers/2016-August/049821.html
>
> The method described there would not work for us. But we should be able
> to rename some of the sections. Compared to my current method (adding an
> attribute to every variable) this would make it simpler to update to a
> newer version with some changed global variables. So it's worth a try.
>
> Kind regards,
>
> Christian Mauderer
>
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