Re: C++ vs. glibc/Hurd/Mach headers

[Thomas Schwinge]

Hi!

On Sun, 27 Nov 2016 17:14:26 +0100, Samuel Thibault <samuel.thibault@gnu.org> 
wrote:
> Thomas Schwinge, on Sat 26 Nov 2016 19:53:34 +0100, wrote:
> > When changing the GDB source code to use kern_return_t (or int) instead
> > of error_t, I still see hurd.h:__hurd_fail and
> > hurd/signal.h:HURD_MSGPORT_RPC choke on their own error_t usage:
> > 
> >     $ echo -e '#include <errno.h>\n#include <mach.h>\n#include 
> > <hurd.h>\n#include <hurd/signal.h>\nvoid f(){ kern_return_t err = 0; err = 
> > thread_get_state(0,0,0,0); err = HURD_MSGPORT_RPC(0,0,0,0); }' | g++ 
> > -D_GNU_SOURCE -x c++ - -S -o /dev/null -O2
> 
> Don't use 0, but ESUCCESS.

;-) I do know about ESUCCESS (I added it), but the literal 0 (int) here
are to model the fact that Mach API calls have a return type of
kern_return_t (int).  (Thus, I will change GDB's "err" variables from
error_t to kern_return_t.)

> >     In file included from /usr/include/errno.h:35:0,
> >                      from <stdin>:1:
> >     /usr/include/hurd.h: In function ‘int __hurd_fail(error_t)’:
> >     /usr/include/hurd.h:60:13: error: invalid conversion from ‘int’ to 
> > ‘error_t {aka __error_t_codes}’ [-fpermissive]
> >            err = EIEIO;
> >                  ^
> >     /usr/include/hurd.h:64:13: error: invalid conversion from ‘int’ to 
> > ‘error_t {aka __error_t_codes}’ [-fpermissive]
> >            err = ENOMEM;
> >                  ^
> >     /usr/include/hurd.h:68:13: error: invalid conversion from ‘int’ to 
> > ‘error_t {aka __error_t_codes}’ [-fpermissive]
> >            err = EINVAL;

This remains to be fixed; can you please commit your patch?

> The HURD_MSGPORT_RPC seems missing casts between kern_error and error_t
> indeed.

Thanks for changing this code.  Though, the explicit casts are also not
completely ideal, as they now hide other kinds of problems, for example:

    $ echo -e '#include <errno.h>\n#include <hurd.h>\n#include 
<hurd/signal.h>\nvoid f(){ error_t err = HURD_MSGPORT_RPC(&err,&err,&err,&err); 
}' | gcc -D_GNU_SOURCE -x c - -S -o /dev/null -O2

... in C compilation mode now no longer diagnoses "error: incompatible
types when assigning [...]".  Oh well...  ;-/


Grüße
 Thomas