<rpc/rpc.h> and rpc_createerr

[Heyman, Jerrold]

> -----Original Message-----
> From: owner-freebsd-hackers at freebsd.org [mailto:owner-freebsd-hackers at freebsd.org] On Behalf Of Kurt
> Lidl
> Sent: Friday, December 11, 2015 3:59 PM
> To: freebsd-hackers at freebsd.org
> Subject: Re: <rpc/rpc.h> and rpc_createerr
> 
> On 12/11/15 10:22 AM, Heyman, Jerrold wrote:
> > Originally posted to freebsd-questions, which recommended I come here
> >
> > I've just installed FreeBSD 10.2 in order to determine the portability
> > of my companies code.  Built gcc4.6 out of the ports/lang area, but
> > see the same issue using /usr/bin/cc (clang 3.4.1).
> >
> > in /usr/include/rpc/clnt.h the following snippet:
> >
> > /*
> > * If a creation fails, the following allows the user to figure out why.
> > */
> > struct rpc_createerr {
> >          enum clnt_stat cf_stat;
> >          struct rpc_err cf_error;  /* userful when cf_stat ==
> > RPC_PMAPFAILURE */ };
> >
> > __BEGIN_DECLS
> > extern struct rpc_createerr    *__rpc_createeer(void);
> > __END_DECLS
> > #define rpc_createerr          (*(__rpc_createeerr()))
> >
> > Note that the #define becomes active once the file is included, and in
> > my source code I have multiple
> >
> >     struct rpc_createerr *ce;
> >
> > declarations.  Both cc and gcc cite this as an error, though for different reasons.
> >
> > gcc complains that a '(' is found where a '{' is expected.
> > The cc error message is 'error: declaration of anyonymous struct must be a definition'.
> >
> > My other ports - Linux, AIX, Solaris, Mac OSX, do not have the #define in /usr/include/rpc/clnt.h.
> > The HP-UX does, but it is encapsulated within a #ifdef _REENTRANT / #endif block.
> >
> > Is this an actual error, or is there something on FreeBSD that I need
> > to do that is different than the other platforms?
> 
> Well, the rpc_clnt_client(3) manpage says:
> 
> >      struct rpc_createerr rpc_createerr;
> >               A global variable whose value is set by any RPC client handle
> >               creation routine that fails.  It is used by the routine
> >               clnt_pcreateerror() to print the reason for the failure.
> 
> As a global variable, I'm not sure how you're going to have multiple different ones...
> 
> The following code compiles with no warnings -- note that the rpc_createerr structure isn't allocated (explictly) in
> this code.
> 
> #include <rpc/rpc.h>
> int main(int argc, char *argv[])
> {
> 	CLIENT *client = NULL;
> 
> 	client = clnt_create("localhost", 1, 1, "udp");
> 
> 	if (client == NULL)
> 		return ((int)rpc_createerr.cf_stat);
> 
> 	return 0;
> }

Kurt,

Compiling the above example code with -E gives the following for the return((int)rpc_createerr.cf_stat); line

return ((int)(*(__rpc_createerr())).cf_stat);

which is what is expected based on the #define.

Adding a declaration, 'struct rpc_createerr *ce;' results in the generation of

struct (*(__rpc_createerr())) *ce;

Using (-E) compile option.  Again, correct textual substitution for the #define, but when compiling with -c I get the following 

tester.c:6:4 error: declaration of anonymous struct must be a definition
     struct rpc_createerr *ce;
     ^
tester.c:6:4: warning: declaration does not declare anything [-Wmissing-declarations]
    struct rpc_createerr *ce;
    ^^^^^

Jerry
Jerry Heyman                            | 
Principal Software Engineer             |   Software is the difference between
EMC Data Domain                         |    hardware and reality
Jerrold.Heyman at emc.com / 919.597.7812   |