Messages in this thread | | | Date | Fri, 18 Jul 2014 13:15:17 -0700 | From | "H. Peter Anvin" <> | Subject | Re: linux-next: build warning after merge of the tip tree |
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On 07/18/2014 01:08 PM, Andy Lutomirski wrote: > > 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. >
No, the issue is that gcc is telling you that the code will do the wrong thing in this case. Yes, only for one iteration, but still.
The reason this is a concern is that: (x > x + n) and its variants is often used to mean (x > INT_MAX - n) without the type knowledge, but that is actually invalid standard C because signed types are not guaranteed to wrap.
-hpa
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