Re: Commit fcd8843c40 breaks old compilers

[Boris Ostrovsky]

On 11/18/2017 12:39 PM, Trond Myklebust wrote:
> On Sat, 2017-11-18 at 12:19 -0500, Boris Ostrovsky wrote:
> > Commit fcd8843c406b46433857ae45e5e9d84b01a7d20b breaks on older
> > compilers which cannot process initializers for anonymous structures:
> >
> > +const nfs4_stateid invalid_stateid = {
> > +       {
> > +               .seqid = cpu_to_be32(0xffffffffU),
> > +               .other = { 0 },
> > +       },
> > +       .type = NFS4_INVALID_STATEID_TYPE,
> > +};
> >
> >
> > /home/build/linux-linus/fs/nfs/nfs4state.c:74: error: unknown field
> > âseqidâ specified in initializer
> > /home/build/linux-linus/fs/nfs/nfs4state.c:74: warning: missing
> > braces
> > around initializer
> > /home/build/linux-linus/fs/nfs/nfs4state.c:74: warning: (near
> > initialization for âinvalid_stateid.<anonymous>.dataâ)
> > /home/build/linux-linus/fs/nfs/nfs4state.c:74: warning: overflow in
> > implicit constant conversion
> > /home/build/linux-linus/fs/nfs/nfs4state.c:75: error: unknown field
> > âotherâ specified in initializer
> > /home/build/linux-linus/fs/nfs/nfs4state.c:75: error: extra brace
> > group
> > at end of initializer
> > /home/build/linux-linus/fs/nfs/nfs4state.c:75: error: (near
> > initialization for âinvalid_stateid.<anonymous>â)
> > /home/build/linux-linus/fs/nfs/nfs4state.c:75: warning: excess
> > elements
> > in union initializer
> > /home/build/linux-linus/fs/nfs/nfs4state.c:75: warning: (near
> > initialization for âinvalid_stateid.<anonymous>â)
> > make[4]: *** [fs/nfs/nfs4state.o] Error 1
> > make[3]: *** [fs/nfs] Error 2
> >
> >
> > FC-64 <build@build-mk2:~> gcc --version
> > gcc (GCC) 4.4.4 20100503 (Red Hat 4.4.4-2)
> >
> >
> > A similar bug was fixed by e0714ec4f9efe7b86828b0dcc077fd8f5d8e5e91
> > but
> > I don't think the same approach can work here.
>
>
> I don't have any setups with gcc 4.4.4. What is it expecting here? Is
> it expecting an extra set of braces due to the anonymous "struct"?

No, that won't work (at least I couldn't get it to work) because the 
solution from e0714ec4f9e assumes that the anonymous struct is the first 
one in the enveloping struct.

It worked only if I (this is a small C program with equivalent structs):

struct nfs4_stateid_struct {
        union {
                //char data[4];
                struct {
                        unsigned seqid;
                        char other[6];
                } __attribute__ ((packed));
		char data[4];
        };
and then

const nfs4_stateid invalid_stateid = {
        {
                  {.seqid = 0xffffffffU,
                  .other = { 0 } },
        },
        .type = NFS4_INVALID_STATEID_TYPE,
};

If I keep data[4] where it is now I get compiler error

an.c:35:20: error: field name not in record or union initializer
                   {.seqid = 0xffffffffU,
                    ^
an.c:35:20: note: (near initialization for 
'invalid_stateid.<anonymous>.data')
an.c:35:29: warning: overflow in implicit constant conversion [-Woverflow]
                   {.seqid = 0xffffffffU,
                             ^~~~~~~~~~~
an.c:36:19: error: field name not in record or union initializer
                   .other = { 0 } },
                   ^
an.c:36:19: note: (near initialization for 
'invalid_stateid.<anonymous>.data')
an.c:36:19: warning: braces around scalar initializer
an.c:36:19: note: (near initialization for 
'invalid_stateid.<anonymous>.data[1]')

I don't know if you want to change public header file just to get around 
this problem.


-boris