Re: [Xen-devel] bogus wrap check in xen-netback

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Apr 25, 2018 at 04:26:06AM -0600, Jan Beulich wrote:
> >>> On 25.04.18 at 12:06, <wei.liu2@xxxxxxxxxx> wrote:
> > On Wed, Apr 25, 2018 at 11:04:26AM +0200, Olaf Hering wrote:
> >> Am Wed, 25 Apr 2018 09:59:23 +0100
> >> schrieb Wei Liu <wei.liu2@xxxxxxxxxx>:
> >> 
> >> > Do you have the full diff of your changes? 
> >> 
> >> Not right now. But without 'val', or val being uint, the same error 
> >> happens 
> > in f():
> >> 
> >> #include <stdio.h>
> >> void f(void)
> >> {
> >>         unsigned short req_prod = 0, req_cons = 65400;
> >>         unsigned short val;
> >>         val = req_prod - req_cons;
> >>         printf("req_prod - req_cons %u\n", val);
> >>         printf("req_prod - req_cons %x\n", val);
> >> }
> > 
> > What Jan said.
> > 
> > Integer promotion makes unsigned short into unsigned int first then do
> > the calculation.
> 
> Not exactly - it promotes to plain (i.e. signed) int.

My bad. Yes, they are converted to int, not unsigned int.

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel