Re: gnunet-config and build informations (bug #5708)

[Christian Grothoff]

On 25.07.21 15:23, Alessio Vanni wrote:
> Hello,
> 
> Christian Grothoff <grothoff@gnunet.org> writes:
> 
>> GNU Taler has taler-config, which recycles gnunet-config in a funky way
>> using LD_PRELOAD:
>>
>> https://git.taler.net/exchange.git/tree/src/util/taler-config.in
>>
>> This works, because there is:
>> https://git.taler.net/exchange.git/tree/src/util/os_installation.c
>>
>> which overrides gnunet-config settings to turn it into taler-config!
>>
>> So _ideally_, we would use the GNUNET_OS_ProjectData instead of directly
>> using hard-coded values for the output of the new flags. That way, we
>> could modify GNU Taler so that taler-config will not return the GNUnet
>> flags, but the Taler flags (again using preload, without copying the
>> source!)
> 
> I don't follow Taler's development, so I didn't know about this "trick".
> Thanks for reporting.

Sure, it is very non-obvious ;-).

> I'm going to push a patch to change the hardcoded values to something
> based on the values returned by `GNUNET_OS_installation_get_path'.
> Hopefully that's going to work for Taler, as I can't think of any other
> way to have it print the includedir and the libdir otherwise :)

I suggest youy pass all of the information (also possibly via #define's)
into the GNUNET_OS_ProjectData and grab it from there! That way, Taler
can override it without having to change gnunet-config itself.

> As a side note, to keep gnunet-config coherent with the pkg-config
> definition, I also had it print `-lgnunetutil' when using the `--libs'
> flag.
> 
> I don't know how Taler handles its public APIs, if it has any, so if an
> application wants to compile against Taler it would be useful to have
> taler-config also print e.g. `-ltalerutil'.

Yes, it is similar. So you should get the "-gnunetutil" also from some
new field you add to the GNUNET_OS_ProjectData. Ideally, you could even
put an array of command-line options into GNUNET_OS_ProjectData, so that
all of the new functions you add becomes fully customizable via LD_PRELOADs.

> I doubt this is something that gnunet-config can handle internally, so
> if Taler (or any application using the LD_PRELOAD + gnunet-config combo)
> has special needs for the `--libs' (or even the `--cflags') flag, the
> execution with that flag should be intercepted somehow and the
> appropriate values appended to the default output of gnunet-config.

My point was the "intercepted somehow" we should use is the
customization via the GNUNET_OS_ProjectData!

Happy hacking!

Christian