Re: Don't Plan 9 C compiler initialize the rest of member of a?struct?

On Mon, Apr 01, 2019 at 09:20:43PM -0400, Dan Cross wrote:
> On Mon, Apr 1, 2019 at 8:36 PM Kurt H Maier <[email protected]> wrote:
> 
> > On Mon, Apr 01, 2019 at 08:26:30PM -0400, Jeremy O'Brien wrote:
> > > On Mon, Apr 1, 2019, at 11:33, Kyohei Kadota wrote:
> > > > Hi, 9fans. I use 9legacy.
> > > >
> > > > About below program, I expected that flags field will initialize to
> > > > zero but the value of flags was a garbage, ex, "f8f7".
> > > > Is this expected?
> > > >
> > > > ```
> > > > #include <stdio.h>
> > > >
> > > > struct option {
> > > >     int n;
> > > >     char *s;
> > > >     int flags;
> > > > };
> > > >
> > > > int
> > > > main(void)
> > > > {
> > > >     struct option opt = {1, "test"};
> > > >     printf("%d %s %x\n", opt.n, opt.s, opt.flags);
> > > >     return 0;
> > > > }
> > > > ```
> > > >
> > > >
> > >
> > > According to C99: "If an object that has automatic storage duration is
> > not initialized explicitly, its value is indeterminate."
> > >
> > > Stack variable == automatic storage duration. This appears to be correct
> > behavior to me.
> > >
> >
> > Can anyone provide the patches 9legacy uses to implement C99 compliance?
> 
> 
> There were actually quite a few of them, mostly done by Geoff Collyer.  The
> compiler sources list contains a list of desiderata in a file called `c99`;
> of course, the plan9 compilers aren't completely compliant (they weren't
> trying to be). Incidentally this file has been carried forward into, for
> example, /sys/src/cmd/cc/c99 in the 9front distribution (and other plan9
> derivatives).
> 
> In the present case, this appears to be a compiler bug. The aforementioned
> reference to n1548 sec 6.7.9 para 10 is incorrect in that there _is_ an
> explicit initializer here. The relevant text in the standard is sec 6.7.9
> pp 16-21, which specifies that in the event that an explicit initializer
> does not completely cover (in a topological sense) the thing it is
> initializing, then the elements not covered shall be initialized as if they
> had _static_ storage duration; that is, they should be zeroed.
> 
> Now as I said, the Plan 9 C compilers aren't explicit C99 compliant. But
> given that the `c99` file describes things related to initializer lists as
> being unneeded because they were already implemented, one may assume it was
> believed that this was covered by c99 behavior. It isn't.
> 
>         - Dan C.

So, no?

khm