Re: test-math.c:89:3: runtime error: division by zero

[Jeffrey Walton]

On Sun, Mar 29, 2020 at 7:21 PM Jeffrey Walton <address@hidden> wrote:
>
> On Sun, Mar 29, 2020 at 5:59 PM Bruno Haible <address@hidden> wrote:
> >
> > Jeffrey Walton wrote:
> > > Let's see what the GCC folks recommend: "GCC and division by 0 under
> > > sanitizers", 
> > > https://gcc.gnu.org/pipermail/gcc-help/2020-March/138746.html.
> >
> > The way I interpret their answer
> > https://gcc.gnu.org/pipermail/gcc-help/2020-March/138747.html
> > is:
> > 1) You need to distinguish integer division by zero and floating-point
> >    division by zero.
> > 2) For floating-point division by zero GCC warns but should not warn.
> >    You should enter a bug report about this.
> > 3) The undefined-behaviour sanitizer should report integer division by zero
> >    but not floating-point division by zero ("as it can be a legitimate way
> >    of obtaining infinities and NaNs").
> >
> > In the gnulib code, test-math.c:89, we clearly have a floating-point
> > division by zero.
>
> Yeah, GCC looks partially clean. It is not producing a sanitizer
> finding, so I guess no blood, no foul.
>
> Clang is a problem: https://bugs.llvm.org/show_bug.cgi?id=45352.

Here's a workaround, but I think it looks like fido's ass:

$ cat test.c
#include <float.h>
#include <math.h>

#if defined(__clang__)
# define CLANG_NO_DIV_BY_ZERO
__attribute__((no_sanitize("float-divide-by-zero")))
#else
# define CLANG_NO_DIV_BY_ZERO
#endif

CLANG_NO_DIV_BY_ZERO
int main(void)
{
  return INFINITY == 1.0f / 0.0f ? 0 : 1;
}

$ clang -fsanitize=undefined test.c -o test.exe
$ ./test.exe
$ clang --version
clang version 6.0.0-1ubuntu2

Would you be willing to hide a macro like CLANG_NO_DIV_BY_ZERO in a
header somewhere so it can be used in tests like test-math.h?

Jeff