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Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gJfoG-0006kE-Li; Mon, 05 Nov 2018 14:24:57 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3223A2029F9FF; Mon, 5 Nov 2018 15:24:53 +0100 (CET) Date: Mon, 5 Nov 2018 15:24:53 +0100 From: Peter Zijlstra To: Andrey Ryabinin Cc: Trond Myklebust , "mark.rutland@arm.com" , "linux-kernel@vger.kernel.org" , "ralf@linux-mips.org" , "jlayton@kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "bfields@fieldses.org" , "linux-mips@linux-mips.org" , "linux@roeck-us.net" , "linux-nfs@vger.kernel.org" , "akpm@linux-foundation.org" , "will.deacon@arm.com" , "boqun.feng@gmail.com" , "paul.burton@mips.com" , "anna.schumaker@netapp.com" , "jhogan@kernel.org" , "netdev@vger.kernel.org" , "davem@davemloft.net" , "arnd@arndb.de" , "paulus@samba.org" , "mpe@ellerman.id.au" , "benh@kernel.crashing.org" , Paul McKenney , dvyukov@google.com, willy@infradead.org Subject: Re: [RFC PATCH] lib: Introduce generic __cmpxchg_u64() and use it where needed Message-ID: <20181105142453.GA22449@hirez.programming.kicks-ass.net> References: <1541015538-11382-1-git-send-email-linux@roeck-us.net> <20181031213240.zhh7dfcm47ucuyfl@pburton-laptop> <20181031220253.GA15505@roeck-us.net> <20181031233235.qbedw3pinxcuk7me@pburton-laptop> <4e2438a23d2edf03368950a72ec058d1d299c32e.camel@hammerspace.com> <20181101131846.biyilr2msonljmij@lakrids.cambridge.arm.com> <20181101145926.GE3178@hirez.programming.kicks-ass.net> <20181101163212.GF3159@hirez.programming.kicks-ass.net> <5a846924-e642-d9d1-4e0e-810bd4d01c26@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5a846924-e642-d9d1-4e0e-810bd4d01c26@virtuozzo.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Fri, Nov 02, 2018 at 07:19:15PM +0300, Andrey Ryabinin wrote: > UBSAN warns about signed overflows despite -fno-strict-overflow if gcc version is < 8. > I have learned recently that UBSAN in GCC 8 ignores signed overflows if -fno-strict-overflow of fwrapv is used. > > $ cat signed_overflow.c > #include > > __attribute__((noinline)) > int foo(int a, int b) > { > return a+b; s/+/< } > > int main(void) > { > int a = 0x7fffffff; > int b = 2; > printf("%d\n", foo(a,b)); > return 0; > } It also seem to affect 'shift': peterz@hirez:~/tmp$ gcc -fsanitize=signed-integer-overflow,shift overflow.c ; ./a.out overflow.c:6:11: runtime error: left shift of 2147483647 by 2 places cannot be represented in type 'int' -4 peterz@hirez:~/tmp$ gcc -fsanitize=signed-integer-overflow,shift -fwrapv overflow.c ; ./a.out -4