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

On 7/2/19 5:37 pm, Segher Boessenkool wrote:

On Thu, Feb 07, 2019 at 04:33:23PM +1100, Andrew Donnellan wrote:

quoted

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).

The table is never length 0, it's a statically defined array.

Segher

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan@au1.ibm.com  IBM Australia Limited