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>

# realloc.m4 serial 12
dnl Copyright (C) 2007, 2009-2011 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.

# gl_FUNC_REALLOC_GNU
# -------------------
# Test whether 'realloc (0, 0)' is handled like in GNU libc, and replace
# realloc if it is not.
AC_DEFUN([gl_FUNC_REALLOC_GNU],
[
  AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
  dnl _AC_FUNC_REALLOC_IF is defined in Autoconf.
  _AC_FUNC_REALLOC_IF(
    [AC_DEFINE([HAVE_REALLOC_GNU], [1],
               [Define to 1 if your system has a GNU libc compatible 'realloc'
                function, and to 0 otherwise.])],
    [AC_DEFINE([HAVE_REALLOC_GNU], [0])
     REPLACE_REALLOC=1
    ])
])# gl_FUNC_REALLOC_GNU

# gl_FUNC_REALLOC_POSIX
# ---------------------
# Test whether 'realloc' is POSIX compliant (sets errno to ENOMEM when it
# fails), and replace realloc if it is not.
AC_DEFUN([gl_FUNC_REALLOC_POSIX],
[
  AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
  AC_REQUIRE([gl_CHECK_MALLOC_POSIX])
  if test $gl_cv_func_malloc_posix = yes; then
    AC_DEFINE([HAVE_REALLOC_POSIX], [1],
      [Define if the 'realloc' function is POSIX compliant.])
  else
    REPLACE_REALLOC=1
  fi
])