Re: Jenkins build is still unstable: FreeBSD_HEAD-tests2 #867

On 22 Mar 2015, at 22:32, Craig Rodrigues <rodrigc_at_FreeBSD.org> wrote:
> 
> On Sun, Mar 22, 2015 at 2:29 PM, Dimitry Andric <dim_at_freebsd.org> wrote:
> 
> Ah right, that was on i386, on amd64 it does result in -2^63.  It is indeed caused by reliance on signed integer wrapping.
> 
> This diff should fix it, without rewriting the utility:
> 
> Index: bin/expr/Makefile
> ===================================================================
> --- bin/expr/Makefile   (revision 280156)
> +++ bin/expr/Makefile   (working copy)
> _at__at_ -6,6 +6,9 _at__at_ PROG=   expr
>  SRCS=  expr.y
>  YFLAGS=
> 
> +# expr relies on signed integer wrapping
> +CFLAGS+= -fwrapv
> +
>  NO_WMISSING_VARIABLE_DECLARATIONS=
> 
>  .if ${MK_TESTS} != "no"
> 
> 
> Well, another alternative is to patch expr.y:
> 
> Index: expr.y
> ===================================================================
> --- expr.y      (revision 280353)
> +++ expr.y      (working copy)
> _at__at_ -393,7 +393,7 _at__at_
>  }
> 
>  void
> -assert_plus(intmax_t a, intmax_t b, intmax_t r)
> +assert_plus(intmax_t a, intmax_t b, volatile intmax_t r)
>  {
>         /*
>          * sum of two positive numbers must be positive,
> _at__at_ -420,7 +420,7 _at__at_
>  }
> 
>  void
> -assert_minus(intmax_t a, intmax_t b, intmax_t r)
> +assert_minus(intmax_t a, intmax_t b, volatile intmax_t r)
>  {
>         /* special case subtraction of INTMAX_MIN */
>         if (b == INTMAX_MIN && a < 0)
> 
> 
> There were already some patches previously done to this
> file to add "volatile", so maybe this would be OK to do.
> 
> What do you think?

Volatile is not the solution, it is completely orthogonal.  The correct
way would be to use unsigned integers, for which wrapping is defined,
then convert those back and forth when presenting the results to the
user.

-Dimitry