Re: undefined behavior in closeout, aggravated by libsigsegv

[Bruno Haible]

Eric Blake wrote:
> That is ONLY possible if both:
> stdin was closed
> the user is not using freopen_safer
> ...
> I'd rather make the patch conditional on whether freopen_safer is also in use.

I see. How about this?

2009-11-22  Bruno Haible  <address@hidden>

        error: account for the possibility of freopen (stdout).
        * lib/error.c (error, error_at_line): Use fileno (stdout) instead of 1.

*** lib/error.c.orig    2009-11-22 17:02:20.000000000 +0100
--- lib/error.c 2009-11-22 17:02:10.000000000 +0100
***************
*** 238,250 ****
                   0);
  #endif
  
  #if !_LIBC && defined F_GETFL
!   /* POSIX states that fflush (stdout) after fclose is unspecified; it
!      is safe in glibc, but not on all other platforms.  fflush (NULL)
!      is always defined, but too draconian.  */
!   if (0 <= fcntl (1, F_GETFL))
  #endif
!   fflush (stdout);
  #ifdef _LIBC
    _IO_flockfile (stderr);
  #endif
--- 238,265 ----
                   0);
  #endif
  
+   {
  #if !_LIBC && defined F_GETFL
!     int stdout_fd;
! 
! # if GNULIB_FREOPEN_SAFER
!     /* Use of gnulib's freopen-safer module normally ensures that
!        fileno (stdout) == 1  always.  */
!     stdout_fd = 1;
! # else
!     /* POSIX states that fileno (stdout) after fclose is unspecified.  But in
!        practice it is not a problem, because stdout is statically allocated 
and
!        the fd of a FILE stream is stored as a field in its allocated memory.  
*/
!     stdout_fd = fileno (stdout);
! # endif
!     /* POSIX states that fflush (stdout) after fclose is unspecified; it
!        is safe in glibc, but not on all other platforms.  fflush (NULL)
!        is always defined, but too draconian.  */
!     if (0 <= stdout_fd && 0 <= fcntl (stdout_fd, F_GETFL))
  #endif
!       fflush (stdout);
!   }
! 
  #ifdef _LIBC
    _IO_flockfile (stderr);
  #endif
***************
*** 303,315 ****
                   0);
  #endif
  
  #if !_LIBC && defined F_GETFL
!   /* POSIX states that fflush (stdout) after fclose is unspecified; it
!      is safe in glibc, but not on all other platforms.  fflush (NULL)
!      is always defined, but too draconian.  */
!   if (0 <= fcntl (1, F_GETFL))
  #endif
!   fflush (stdout);
  #ifdef _LIBC
    _IO_flockfile (stderr);
  #endif
--- 318,345 ----
                   0);
  #endif
  
+   {
  #if !_LIBC && defined F_GETFL
!     int stdout_fd;
! 
! # if GNULIB_FREOPEN_SAFER
!     /* Use of gnulib's freopen-safer module normally ensures that
!        fileno (stdout) == 1  always.  */
!     stdout_fd = 1;
! # else
!     /* POSIX states that fileno (stdout) after fclose is unspecified.  But in
!        practice it is not a problem, because stdout is statically allocated 
and
!        the fd of a FILE stream is stored as a field in its allocated memory.  
*/
!     stdout_fd = fileno (stdout);
! # endif
!     /* POSIX states that fflush (stdout) after fclose is unspecified; it
!        is safe in glibc, but not on all other platforms.  fflush (NULL)
!        is always defined, but too draconian.  */
!     if (0 <= stdout_fd && 0 <= fcntl (stdout_fd, F_GETFL))
  #endif
!       fflush (stdout);
!   }
! 
  #ifdef _LIBC
    _IO_flockfile (stderr);
  #endif