Re: 32-bit bug in iovec iterator changes

James Bottomley
2014-06-22T01:00:37Z

On Sun, 2014-06-22 at 01:53 +0100, Al Viro wrote:
> On Sat, Jun 21, 2014 at 05:32:44PM -0700, James Bottomley wrote:
> > > No, we are not. Look:
> > > * comparison promotes both operands to u64 here, so its result is
> > > accurate, no matter how large count is. They are compared as natural
> > > numbers.
> >
> > True ... figured this out 10 seconds after sending the email.
> >
> > > * assignment converts count to size_t, which *would* truncate for
> > > values that are greater than the maximal value representable by size_t.
> > > But in that case it's by definition greater than i->count, so we do not
> > > reach that assignment at all.
> >
> > OK, so what I still don't get is why isn't the compiler warning when we
> > truncate a u64 to a u32? We should get that warning in your new code,
> > and we should have got that warning in fs/block_dev.c where it would
> > have pinpointed the actual problem.
>
> In which universe?
>
> extern void f(unsigned int);
>
> void g(unsigned long x)
> {
> f(x);
> }

In the one where the code is compiled with -Wconversion ... I'm just
surprised, I thought we had this enabled.

James