Subject: Re: [PATCH 1/2] powerpc/64s: Work around spurious warning on old gccs with -fsanitize-coverage

From: Segher Boessenkool <[email-masked]>
Date: Thu, 7 Feb 2019 00:37:37 -0600

On Thu, Feb 07, 2019 at 04:33:23PM +1100, Andrew Donnellan wrote:
> Some older gccs (<GCC 7), when invoked with -fsanitize-coverage=trace-pc,
> cause a spurious uninitialised variable warning in dt_cpu_ftrs.c:
> 
>   arch/powerpc/kernel/dt_cpu_ftrs.c: In function ‘cpufeatures_process_feature’:
>   arch/powerpc/kernel/dt_cpu_ftrs.c:686:7: warning: ‘m’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>     if (m->cpu_ftr_bit_mask)

It seems to me the warning is correct?  If enable_unknown is false and no
cpu_feature is found, it will in

	if (m->cpu_ftr_bit_mask)
		cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;

enable random features (whatever was last in the table), or indeed access
via NULL if the table is length 0?  So maybe this should be

	if (known && m->cpu_ftr_bit_mask)
		cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;

instead?  (The code would be much clearer if all the known vs. !known
codepath was fully separated here).

Segher