Re: [musl] bug: integer overflow in memmem()

[Jeffrey Walton <noloader@gmail.com>]

On Thu, Apr 30, 2020 at 2:30 PM Alfred Agrell <alfred@agrell.info> wrote:
>
> To reproduce: Compile src/string/memmem.c with -fsanitize=undefined, then
>
> int main()
> {
>   char a[4] = { -1,-1,-1,-1 };
>   memmem(a, 4, a, 3);
>   memmem(a, 4, a, 4);
> }
>
> Expected result: No output
>
> Actual (Ubuntu 18.04 x86_64, gcc 7.5.0, ):
>
> memmem.c:15:20: runtime error: left shift of 255 by 24 places cannot be
> represented in type 'int'
> memmem.c:16:20: runtime error: left shift of 255 by 24 places cannot be
> represented in type 'int'
> memmem.c:24:20: runtime error: left shift of 255 by 24 places cannot be
> represented in type 'int'
> memmem.c:25:20: runtime error: left shift of 255 by 24 places cannot be
> represented in type 'int'
>...
>
> I'm not aware of any compiler on any platform where it'll actually
> break, so your choice whether this is a real bug. I didn't check if
> similar issues exist elsewhere across musl.

Try Intel ICC. It is ruthless and removes undefined behavior every
chance it gets. It can usually break a program with UB that GCC, Clang
and MSVC compile OK.

Jeff