Re: [PATCH] meson: fix botched compile check conversions

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/16/21 13:00, Daniel P. Berrangé wrote:
> I wonder if the problem is more fundamental than that. Passing
> stuff in --extra-cflags is done to influence the flags used to
> compile the QEMU end user binaries. Unfortunately --extra-cflags
> is also getting applied to all the meson.build feature checks.
> 
> IMHO we would get a more reliable result if the meson.build
> checks were fully isolated from the cflags we used for building
> everything else, so the checks get a well understood, predictable
> environment.
> 
> IIUC, this current behaviour is a result of us adding cflags
> using  add_global_arguments / add_project_arguments.

No, it's not using add_global_arguments/add_project_arguments for 
--extra-cflags.

The --extra-cflags (aka the CFLAGS envvar, or "meson setup -Dc_args") is 
messy: on one hand it's kinda legacy (we have configure flags to set 
-O2, -g, -Werror, etc.), on the other hand not really possible to kill 
it because it's how distros expect to set flags such as -O2.

But it's full of pitfalls, and the only good use of it seems to be for 
-I and -L flags.  We already saw issues with it last week with distros 
adding "-Wall" to CFLAGS or --extra-cflags and that gives you bogus 
warnings.  Unfortunately you certainly want flags such as -g to override 
earlier flags, and you might even want -Wall to override earlier -Wno-* 
flags *unless -Werror is in use*.

Apart from this, the sizeof() issue (which by the way I didn't see with 
GCC) has to be fixed in Meson and is probably visible also in e.g. 
has_members.

Paolo