On Fri, 2020-05-01 at 09:54 +0200, Arnd Bergmann wrote:
> On Fri, May 1, 2020 at 9:48 AM John Garry <john.garry@xxxxxxxxxx>
> wrote:
> > On 30/04/2020 22:30, Arnd Bergmann wrote:
> > > This should really be a flexible-array member, but the structure
> > > already has such a member, swapping it out with sense_data[]
> > > would cause many more warnings elsewhere.
> > >
> >
> >
> > Hi Arnd,
> >
> > If we really prefer flexible-array members over zero-length array
> > members, then could we have a union of flexible-array members? I'm
> > not sure if that's a good idea TBH (or even permitted), as these
> > structures are defined by the SAS spec and good practice to keep as
> > consistent as possible, but just wondering.
>
> gcc does not allow flexible-array members inside of a union, or more
> than one flexible-array member at the end of a structure.
>
> I found one hack that would work, but I think it's too ugly and
> likely not well-defined either:
>
> struct ssp_response_iu {
> ...
> struct {
> u8 dummy[0]; /* a struct must have at least one
> non-flexible member */
If gcc is now warning about zero length members, why isn't it warning
about this one ... are unions temporarily excluded?
> u8 resp_data[]; /* allowed here because it's at
> the one of a struct */
> };
> u8 sense_data[];
> } __attribute__ ((packed));
Let's go back to what the standard says: we want the data beyond the
ssp_response_iu to be addressable either as sense_data if it's an error
return or resp_data if it's a real response. What about trying to use
an alias attribute inside the structure ... will that work on gcc-10?
James
