On Thu, 3 Aug 2017 13:56:45 -0500 Eric Blake <ebl...@redhat.com> wrote:
> On 08/03/2017 01:38 PM, Greg Kurz wrote:
> > The following code snippet spits a warning with gcc-7.1.1-3.fc26 and -Wall
> > on
> > ppc64le AND x86_64:
> >
> > int foo(void)
> > {
> > char empty_array[] = { };
> > int i, ret = 0;
> >
> > for (i = 0; i < (int) (sizeof(empty_array) / sizeof(empty_array[0]));
> > i++) {
> > ret = empty_array[i];
> > }
> >
> > return ret;
> > }
>
> Confirmed. No idea why the cast makes gcc think i is uninitialized.
>
FYI, I've created a BZ to track this issue in gcc:
https://bugzilla.redhat.com/show_bug.cgi?id=1478864
> >
> > If I drop the (int), the warning goes away... and so does the build break
> > of qemu-system-ppc64 on my ppc64le host.
> >
> > I don't have 4.7.1 or 4.6 compilers around but I could check 4.8.5
> > is okay with that change FWIW.
>
> I tested with gcc 4.4.7 on RHEL 6, but -Wtype-limits there didn't warn
> whether or not the (int) was present; it's possible that we still need
> to test with 4.6 or 4.7.1 to see whether it makes a difference.
>
> >
> >> Ok so let's stop losing time about compiler incoherent warnings, using
> >> -Wno-type-limits for GCC < 5...
> >> So we can keep a sane/understandable codebase, using size_t and no (int)
> >> cast.
>
> That's also a possibility, if we still hit old compilers that require
> the (int).
>
> >>
> >
> > If I also convert 'int i' to 'size_t i' then I get the same error as
> > in commit 61c7bbd2:
> >
> > error: comparison of unsigned expression < 0 is always
> > false [-Werror=type-limits]
>
> Confirmed with newer gcc, whether or not the (int) cast is present.
>
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