Meson: CFLAGS and friends leak into cross environment

[oleavr]

Haven't had time to write a test-case for this yet, but just filing here
so this doesn't slip through the cracks once I finish porting Frida to
Meson.

[nirbheek]

If not CFLAGS, what is the alternative?

[oleavr]

If not CFLAGS, what is the alternative?

I would expect the cross-file to provide things in c_args and the like, because Meson also requires a build_machine compiler when cross-compiling, which I'd provide through CC. So it's a bit confusing if CFLAGS then leaks into the host_machine setup, when CC is used to specify the build_machine compiler. (But maybe I misunderstood something and I'm doing it all wrong. 😅)

[jpakkane]

The cross compiler should take args from the cross file and only that.

The native compiler should take args from CFLAGS and only that.

If there is leakage, it is a bug.

[oleavr]

Thanks @jpakkane! Seems to be easy to fix, I'll open a PR shortly.

[nirbheek]

I mean in terms of what environment variable should be used for overriding *FLAGS? There is precedent for CROSS_CFLAGS and CROSS_LDFLAGS, etc. Perhaps for cross-compilation we should look for those?

[jpakkane]

We want to have less knobs for people to fiddle with, not more. Cross build settings should come from the cross file and nowhere else.

[sdroege]

This should also be done for PKG_CONFIG_PATH and probably others, for consistency at least but also for correctness.

[nirbheek]

I still think we should also add support for CROSS_*FLAGS. It is kinda annoying to have to open and edit your cross-info file just for some quick tests.

[aperezdc]

I agree with @nirbheek. Having some kind of way of setting additional flags on top of the ones defined in the cross-file allows to write a cross-file that is part of e.g. a cross-SDK, while still allowing each component built with that SDK to have a few different compiler flags.

[jpakkane]

Hmmm. I was sure that we exposed cross args in a variable just like c_args but apparently we don't. That is a bug that needs fixing.

[nirbheek]

-Dcross_$lang_args would work just as well as an environment variable, I think.