[Skiboot] [PATCH 6/7] llvm-scan-build: fix result of << is undefined
stewart at linux.vnet.ibm.com
Wed Nov 11 10:54:13 AEDT 2015
Benjamin Herrenschmidt <benh at au1.ibm.com> writes:
>> --- a/hw/fsp/fsp.c
>> +++ b/hw/fsp/fsp.c
>> @@ -198,11 +198,15 @@ static struct fsp *fsp_get_active(void)
>> static u64 fsp_get_class_bit(u8 class)
>> + u8 shift;
>> /* Alias classes CE and CF as the FSP has a single queue */
>> if (class == FSP_MCLASS_IPL)
>> class = FSP_MCLASS_SERVICE;
>> - return 1ul << (class - FSP_MCLASS_FIRST);
>> + shift = class - FSP_MCLASS_FIRST;
>> + assert(shift < 64);
>> + return 1ul << shift;
> And that's gross. Don't do that.
> If you want to bound check class, do so with something like
> assert(class >= FSP_MCLASS_FIRST && class < ...)
> But that added shift variable is just hurting my eyes.
It's kind of incredibly awful, and this seems to be a hoop to jump
through to shut LLVM up.
This doesn't squash the warning:
assert((class - FSP_MCLASS_FIRST) < 64);
Which would be semantically the best.. but what's worse is looking at it
again, class is u8, and FSP_MCLASS_FIRST is defined to 0xce - which
means that expression is only ever going to be <=49 which is, amazingly
enough, well within the allowed number of shifs for u64.
I scream LLVM bug instead and will just drop this patch.
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