Re: [PATCH] sfc: use IS_ENABLED() checks for CONFIG_SFC_SRIOV

[Arnd Bergmann]

On Fri, Feb 17, 2023, at 17:13, Edward Cree wrote:
> On 17/02/2023 09:56, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@xxxxxxxx>
>> 
>> One local variable has become unused after a recent change:
>> 
>> drivers/net/ethernet/sfc/ef100_nic.c: In function 'ef100_probe_netdev_pf':
>> drivers/net/ethernet/sfc/ef100_nic.c:1155:21: error: unused variable 'net_dev' [-Werror=unused-variable]
>>   struct net_device *net_dev = efx->net_dev;
>>                      ^~~~~~~
>> 
>> The variable is still used in an #ifdef. Replace the #ifdef with
>> an if(IS_ENABLED()) check that lets the compiler see where it is
>> used, rather than adding another #ifdef.
>
> So we've had Leon telling us[1] to use __maybe_unused, and you're
>  saying to use IS_ENABLED() instead.  Which is right?
> (And does it make any difference to build time?  I'm assuming the
>  compiler is smart enough that this change doesn't affect text
>  size...?)
> -ed

Both are correct, but I prefer the IS_ENABLED() change because it
improves build coverage. The resulting object code should be the
same, as the dead-code-elimination in gcc takes care of removing
it the same way.

If you use the __maybe_uninitialized annotation, you still need
an extra fix to initialize the ef100_probe_netdev_pf() return
code.

      Arnd