Re: linux-next: build warning after merge of the tip tree

Andy Lutomirski
2014-07-18T20:09:13Z

On Fri, Jul 18, 2014 at 1:05 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 07/18/2014 12:57 PM, Andy Lutomirski wrote:
>>
>> This particular warning is IMO in a particularly dumb category: GCC
>> optimizes some code and then warns about a construct that wasn't there
>> in the original code. In this case, I think it unrolled a loop and
>> discovered that one iteration contained a test that was always true.
>> Big deal.
>>
>> (OTOH, the code in question was buggy, but not all for the reason that
>> GCC thought it was.)
>>
>
> if (syms[sym_vvar_start] > syms[i] + 4096)
> fail("%s underruns begin_vvar\n",
> required_syms[i].name);
>
> if i == sym_vvar_start then this is at least a valid warning. It could
> easily be quieted by chaning syms[] to an unsigned array.

Hah -- fooled you, too :)

i isn't an index in to the syms array at all. This code is completely
wrong. See the patch I sent in reply to Stephen's original email.

But, to your earlier point, presumably this could warn:

for (int i = 0; i < 10; i++)
if (array[i] > array[5] + 1)
fail();

I think that's absurd. There's nothing wrong with that code. A given
test should have to be always true or always false on *all* loop
iterations to be flagged, I think.

--Andy

>
> -hpa
>

--
Andy Lutomirski
AMA Capital Management, LLC