Messages in this thread | | | Date | Fri, 18 Jul 2014 13:50:39 -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 01:20 PM, Andy Lutomirski wrote: >> >> 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. > > Right, but the constant in this case is *much* less than INT_MAX. > Anyway, this is moot.
It isn't about the constant (n) at all, it is about the value of x.
> I do wonder whether the kind of people who build hardened kernels > should enable -fwrapv, though.
-fwrapv in gcc makes signed arithmetic strict 2's-complement, which is what I think we want in the kernel. Someone would just have to make sure there isn't some key codepath in the kernel which gets pessimized.
-hpa
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