linux-kernel - Re: [PATCH] hugetlbfs: Fix integer overflow check in hugetlbfs_file

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Message-ID: <ZLFFGLQ6H/9RCaVf@casper.infradead.org>
Date:   Fri, 14 Jul 2023 13:52:40 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     linke li <lilinke99@...il.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Linke Li <lilinke99@...mail.com>, linux-mm@...ck.org,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        trix@...hat.com, ndesaulniers@...gle.com, nathan@...nel.org,
        muchun.song@...ux.dev, mike.kravetz@...cle.com
Subject: Re: [PATCH] hugetlbfs: Fix integer overflow check in
 hugetlbfs_file_mmap()

On Thu, Jul 13, 2023 at 03:55:55PM +0800, linke li wrote:
> > So we're adding code to handle eventual future compiler bugs? That sounds
> > wrong, but maybe I misunderstood the problem you are trying to solve?
> 
> Sorry for not making it clear. My focus is the presence of undefined
> behavior in kernel code.
> Compilers can generate any code for undefined behavior and compiler
> developers will not
> take this as compiler bugs. In my option,  kernel should not have
> undefined behavior.

The point that several people have tried to make to you is that
*this is not undefined behaviour*.  The kernel is compiled with
-fno-strict-overflow which causes the compiler to define signed arithmetic
overflow to behave as twos-complement.  Check the gcc documentation.