Re: errno (was: Weekly reports - B)

[Szabolcs Nagy <nsz@port70.net>]

* Solar Designer <solar@openwall.com> [2011-07-06 15:35:08 +0400]:
> On Mon, Jun 13, 2011 at 12:54:18AM -0400, Rich Felker wrote:
> > ... errno is a macro and has been for a
> > long time (ever since threads) on most systems. It's required by the
> > standard to be an lvalue macro.
> 
> Any idea why glibc has __set_errno() internally instead of assigning to
> its errno directly, then?  The implementation for __set_errno() does a
> direct assignment anyway.  What did the glibc developers need

it seems there was a different definition under sysdeps until

2002-07-19  Ulrich Drepper  <drepper@redhat.com>
    * sysdeps/generic/bits/errno.h: Remove __set_errno definition.
    * ...

and then

2002-11-25  Jakub Jelinek  <jakub@redhat.com>
    * include/errno.h (__set_errno): Define as errno = val
    unconditionally.


in older glibc eg sysdeps/unix/sysv/linux/bits/errno.h had code like

#ifdef _ERRNO_H

# undef EDOM
# undef EILSEQ
# undef ERANGE
# include <linux/errno.h>

/* Linux has no ENOTSUP error code.  */
# define ENOTSUP EOPNOTSUPP

/* Linux also has no ECANCELED error code.  Since it is not used here
   we define it to an invalid value.  */
# define ECANCELED      125
 
# ifndef __ASSEMBLER__
/* We now need a declaration of the `errno' variable.  */
extern int errno;
 
/* Function to get address of global `errno' variable.  */
extern int *__errno_location __P ((void)) __attribute__ ((__const__));

#  if defined _LIBC
/* We wouldn't need a special macro anymore but it is history.  */
#   define __set_errno(val) (*__errno_location ()) = (val)
#  endif /* _LIBC */

#  if !defined _LIBC || defined _LIBC_REENTRANT
/* When using threads, errno is a per-thread value.  */
#   define errno (*__errno_location ())
#  endif
# endif /* !__ASSEMBLER__ */
#endif /* _ERRNO_H */