[Buildroot] [PATCH 1/1] package/boinc: fix build with autoconf >= 2.70

[Thomas Petazzoni]

Hello Fabrice,

On Thu,  7 Oct 2021 18:41:12 +0200
Fabrice Fontaine <fontaine.fabrice at gmail.com> wrote:

> Fix the following build failure raised since bump of autoconf to version
> 2.71 in commit ecd54b65c1f998a7ccd91f7c523e4ff38c4781da and
> http://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=commit;h=ec90049dfcf4538750e61d675d885157fa5ca7f8:
> 
> checking for /home/buildroot/autobuild/instance-0/output-1/host/bin/mips-linux-gnu-gcc options needed to detect all undeclared functions... cannot detect
> configure: error: in `/home/buildroot/autobuild/instance-0/output-1/build/boinc-7.16.18':
> configure: error: cannot make /home/buildroot/autobuild/instance-0/output-1/host/bin/mips-linux-gnu-gcc report undeclared builtins
> 
> This error raised because AC_CHECK_DECLS returns an error due to -mavx
> flag:
> 
> mips-linux-gnu-gcc: error: unrecognized command line option '-mavx'
> 
> To fix this build failure, hard code ac_cv_c_undeclared_builtin_options
> to 'none needed' as removing '-mavx' from CPPFLAGS will hinder the
> detection of xgetbv, xgetbv, __xgetbv, cpuid, _cpuid and __cpuid
> 
> Fixes:
>  - http://autobuild.buildroot.org/results/4b468a5d3bfbff9638316ca930ef791867774aef
> 
> Signed-off-by: Fabrice Fontaine <fontaine.fabrice at gmail.com>

Wow, this was messy, and took me a while to understand. I've even added
a comment in the .mk file itself to explain what's going on.

There is a bug open in upstream Boinc on Github to track this issue,
and they acknowledge that they shouldn't unconditionally pass -mavx,
which really is the root of the problem.

Anyway, in the mean time, I have applied your patch, with an additional
comment, as said above.

Thanks for the good investigation on this one!

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com