[Mesa-dev] -fno-common build failures (default from upcoming gcc release 10)

[Ian Romanick]

On 1/20/20 6:41 AM, Stefan Dirsch wrote:
> Hi
> 
> Starting from the upcoming GCC release 10, the default of -fcommon option will
> change to -fno-common. Due to this we're going to see a lot of build failures

It seems like many of the places where this would occur in Mesa are
likely to be fine... but it would be easy enough to fix by sprinkling
'extern' around (if my understanding of the GCC docs is correct).  It
also seems unlikely that GCC will be able to apply any hypothetical
optimizations to the uses in Mesa.  I think most places where a global
is intended to be isolated, we already decorate it with static.

See also
https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#index-fcommon

We definitely should decide which behavior we want, and we should start
enforcing it sooner rather than later.

> in Mesa drivers like
> 
> multiple definition of `syncobj_handle'; src/amd/vulkan/9198681@@vulkan_radeon at sha/meson-generated_.._radv_entrypoints.c.o (symbol from plugin):(.text+0x0): first defined here
> [  213s]
> /usr/lib64/gcc/x86_64-suse-linux/9/../../../../x86_64-suse-linux/bin/ld:
> src/amd/vulkan/9198681@@vulkan_radeon at sha/radv_wsi_wayland.c.o (symbol from
> plugin): in function `radv_GetPhysicalDeviceWaylandPresentationSupportKHR':
> 
> I'm wondering if there is already anybody working on fixing these issues or is
> it recommended to workaround it by setting -fcommon manually somehow? How can
> the latter be done when using meson/ninja as build tool?

I know you can do it with buildtype=plain, but that may be overkill for
anything other than testing.

> Thanks,
> Stefan
> 
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