Re: [PATCH] Disable type demotion for sanitizer (PR sanitizer/82072)

[Jeff Law <law@redhat.com>]

On 09/01/2017 11:47 AM, Marek Polacek wrote:
> Here, do_narrow and convert_to_integer_1 is demoting signed types to unsigned,
> e.g. for
>   i = i - lmin
> where i is int and lmin is long int, so what we should produce is
>   i = (int) ((long int) i - lmin)
> but instead it produces
>   i = (int) ((unsigned int) i - (unsigned int) lmin);
> which hides the overflow.  Similarly for NEGATE_EXPR.  This patch prevents
> such demoting when the sanitizer is on.
> 
> There still might be a similar issue with division or shifting, but I couldn't
> trigger that.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2017-09-01  Marek Polacek  <polacek@redhat.com>
> 
> 	PR sanitizer/82072
> 	* convert.c (do_narrow): When sanitizing signed integer overflows,
> 	bail out for signed types.
> 	(convert_to_integer_1) <case NEGATE_EXPR>: Likewise.
> 
> 	* c-c++-common/ubsan/pr82072.c: New test.
OK.  There's probably other places that may need similar treatment.  You
might want to peek at shorten_binary_op and shorten_compare to see if
they suffer from similar problems.  We really want them to go away, but
we haven't gotten back to that project since Kai left.

Jeff