strerror_r: fix OpenBSD behavior on 0 OpenBSD treats strerror_r(0,,) as a success, but with a message "Undefined error: 0"; while this is distinct from strerror_r(-1,,) returning "Unknown error: -1", it does not imply success. Meanwhile, if buf is short enough for ERANGE, then we can't use strstr to look for "Unknown" or "Undefined" in the resulting message, like we had been doing for strerror(). Fix this by shifting the burden - now the strerror-override code guarantees that 0 will have an override when needed. * lib/strerror-override.c (strerror_override): Also override 0 when needed. * lib/strerror-override.h (strerror_override): Likewise. * lib/strerror.c (strerror): Simplify, now that 0 override is done earlier. * lib/strerror_r.c (strerror_r): Likewise. * m4/strerror.m4 (gl_FUNC_STRERROR): Split detection of 0 behavior... (gl_FUNC_STRERROR_0): ...into new macro. * m4/strerror_r.m4 (gl_FUNC_STRERROR_R): Replace strerror_r if 0 is overridden. (gl_FUNC_STRERROR_R_WORKS): Avoid extra tests if 0 is broken. * modules/strerror-override (Files): Add strerror.m4. (configure.ac): Also provide override for 0 when needed. * doc/posix-functions/strerror.texi (strerror): Document this. * doc/posix-functions/perror.texi (perror): Likewise. Signed-off-by: Eric Blake <eblake@redhat.com>

# obstack-printf.m4 serial 4
dnl Copyright (C) 2008-2011 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

dnl From Eric Blake.
dnl Test whether obstack_printf() exists.  For now, we assume that
dnl obstack_vprintf behaves identically, so we only test for one.

AC_DEFUN([gl_FUNC_OBSTACK_PRINTF],
[
  dnl Persuade glibc <stdio.h> to declare obstack_printf(), obstack_vprintf().
  AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])

  AC_REQUIRE([gl_STDIO_H_DEFAULTS])
  AC_CHECK_FUNCS_ONCE([obstack_printf])
  if test $ac_cv_func_obstack_printf = no ; then
    gl_REPLACE_OBSTACK_PRINTF
  fi

  gl_DECL_OBSTACK_PRINTF
])

AC_DEFUN([gl_REPLACE_OBSTACK_PRINTF],
[
  AC_REQUIRE([gl_STDIO_H_DEFAULTS])
  if test $ac_cv_func_obstack_printf = yes; then
    REPLACE_OBSTACK_PRINTF=1
  fi
])

dnl Ensure obstack_printf() and obstack_vprintf() are declared
dnl (whether or not they are being replaced).
AC_DEFUN([gl_DECL_OBSTACK_PRINTF],
[
  AC_CHECK_DECLS_ONCE([obstack_printf])
  if test $ac_cv_have_decl_obstack_printf = no; then
    HAVE_DECL_OBSTACK_PRINTF=0
  fi
])