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Date:	Fri, 18 Jul 2014 13:15:17 -0700
From:	"H. Peter Anvin" <>
To:	Andy Lutomirski <>
CC:	Stephen Rothwell <>,
	Thomas Gleixner <>,
	Ingo Molnar <>,
	Peter Zijlstra <>,
	"" <>,
	"" <>,
	Linus Torvalds <>
Subject: Re: linux-next: build warning after merge of the tip tree

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.


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