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Message-ID: <20190215100527.GT21289@port70.net>
Date: Fri, 15 Feb 2019 11:05:27 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Cc: "jounijl@...oo.co.uk" <jounijl@...oo.co.uk>
Subject: Re: "Arithmetic exception" with modulus operator '%'
* jounijl@...oo.co.uk <jounijl@...oo.co.uk> [2019-02-15 03:35:23 +0000]:
> As in the headline. Program stops and prints "Arithmetic exception" at the
> line where the modulus operator '%' is.
>
> I'm compiling in Alpine linux with clang installed from apk:s:
>
> clang -c test.c
> clang -o test test.o
>
> The code is:
>
> ----- snip -----
> unsigned int unum = 0;
> unsigned int umod = 0;
> unsigned int ures = 0;
> ures = unum % umod; // <-- this one
undefined behaviour == anything can happen
the compiler can drop this entirely.
> ----- /snip -----
>
> The variables have some values other than 0.
>
> The environment is:
> The Alpine Linux is installed in Oracle Virtualbox in FreeBSD 12, 64-bit
> Intel.
x86_64 traps mod by 0 (in case the compiler didn't
drop the code path because of ub).
>
> $ uname -a
> Linux localhost 4.14.89-0-vanilla #1-Alpine SMP Tue Dec 18 16:10:10 UTC 2018
> x86_64 GNU/Linux
>
> $ clang --version
> Alpine clang version 5.0.1 (tags/RELEASE_501/final) (based on LLVM 5.0.1)
>
> What does this? Do I need to include some library?
what behaviour do you expect?
>
> w.b.reg., Jouni
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