--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,23 @@
 2011-06-21  Eric Blake  <eblake@redhat.com>
 
+	strerror_r: fix OpenBSD behavior on 0
+	* 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.
+
 	perror: adjust array size
 	* modules/perror (Depends-on): Add strerror-override.
 	* lib/perror.c (perror): Use it to avoid magic number.

--- a/doc/posix-functions/perror.texi
+++ b/doc/posix-functions/perror.texi
@@ -15,7 +15,7 @@
 @item
 This function treats @code{errno} of 0 like failure, although POSIX
 requires that the message declare it as a success, on some platforms:
-FreeBSD 8.2, MacOS X 10.5.
+FreeBSD 8.2, OpenBSD 4.7, MacOS X 10.5.
 @item
 This function clobbers the @code{strerror} buffer on some platforms:
 Cygwin 1.7.9.

--- a/doc/posix-functions/strerror.texi
+++ b/doc/posix-functions/strerror.texi
@@ -17,7 +17,7 @@
 @code{errno} or using a string similar to out-of-range values),
 although POSIX requires this to leave @code{errno} unchanged and
 report success, on some platforms:
-FreeBSD 8.2, MacOS X 10.5.
+FreeBSD 8.2, OpenBSD 4.7, MacOS X 10.5.
 @item
 This function fails to return a string for out-of-range integers on
 some platforms:

--- a/lib/strerror-override.c
+++ b/lib/strerror-override.c
@@ -37,6 +37,11 @@
   /* These error messages are taken from glibc/sysdeps/gnu/errlist.c.  */
   switch (errnum)
     {
+#if REPLACE_STRERROR_0
+    case 0:
+      return "Success";
+#endif
+
 #if GNULIB_defined_ETXTBSY
     case ETXTBSY:
       return "Text file busy";

--- a/lib/strerror-override.h
+++ b/lib/strerror-override.h
@@ -40,7 +40,8 @@
     || GNULIB_defined_ENOTSUP \
     || GNULIB_defined_ESTALE \
     || GNULIB_defined_EDQUOT \
-    || GNULIB_defined_ECANCELED
+    || GNULIB_defined_ECANCELED \
+    || REPLACE_STRERROR_0
 extern const char *strerror_override (int errnum);
 # else
 #  define strerror_override(ignored) NULL

--- a/lib/strerror.c
+++ b/lib/strerror.c
@@ -45,20 +45,7 @@
   if (msg)
     return (char *) msg;
 
-  /* FreeBSD rejects 0; see http://austingroupbugs.net/view.php?id=382.
-     MacOS X 10.5 does not distinguish 0 from -1.  */
-  if (n)
-    msg = strerror (n);
-  else
-    {
-      int saved_errno = errno;
-      errno = 0;
-      msg = strerror (n);
-      if (errno || (msg &&
-                    (strstr (msg, "nknown") || strstr (msg, "ndefined"))))
-        msg = "Success";
-      errno = saved_errno;
-    }
+  msg = strerror (n);
 
   /* Our strerror_r implementation might use the system's strerror
      buffer, so all other clients of strerror have to see the error

--- a/lib/strerror_r.c
+++ b/lib/strerror_r.c
@@ -209,17 +209,6 @@
     if (ret < 0)
       ret = errno;
 
-    /* FreeBSD rejects 0; see http://austingroupbugs.net/view.php?id=382.
-       MacOS X 10.5 strerror_r differs from the strerror string for 0.  */
-    if (errnum == 0)
-      {
-# if defined __APPLE__ && defined __MACH__
-        ret = EINVAL;
-# endif
-        if (ret == EINVAL)
-          ret = safe_copy (buf, buflen, "Success");
-      }
-
 #else /* USE_SYSTEM_STRERROR */
 
     /* Try to do what strerror (errnum) does, but without clobbering the

--- a/m4/strerror.m4
+++ b/m4/strerror.m4
@@ -1,4 +1,4 @@
-# strerror.m4 serial 15
+# strerror.m4 serial 16
 dnl Copyright (C) 2002, 2007-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -8,33 +8,24 @@
 [
   AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
   AC_REQUIRE([gl_HEADER_ERRNO_H])
+  AC_REQUIRE([gl_FUNC_STRERROR_0])
   m4_ifdef([gl_FUNC_STRERROR_R_WORKS], [
     AC_REQUIRE([gl_FUNC_STRERROR_R_WORKS])
   ])
-  if test -z "$ERRNO_H"; then
+  if test "$ERRNO_H:$REPLACE_STRERROR_0" = :0; then
     AC_CACHE_CHECK([for working strerror function],
      [gl_cv_func_working_strerror],
      [AC_RUN_IFELSE(
         [AC_LANG_PROGRAM(
            [[#include <string.h>
-             #include <errno.h>
            ]],
-           [[int result = 0;
-             char *str;
-             if (!*strerror (-2)) result |= 1;
-             errno = 0;
-             str = strerror (0);
-             if (!*str) result |= 2;
-             if (errno) result |= 4;
-             if (strstr (str, "nknown") || strstr (str, "ndefined"))
-               result |= 8;
-             return result;]])],
+           [[if (!*strerror (-2)) return 1;]])],
         [gl_cv_func_working_strerror=yes],
         [gl_cv_func_working_strerror=no],
         [dnl Be pessimistic on cross-compiles for now.
-         gl_cv_func_working_strerror=no])
+         gl_cv_func_working_strerror="guessing no"])
     ])
-    if test $gl_cv_func_working_strerror = no; then
+    if test "$gl_cv_func_working_strerror" != yes; then
       dnl The system's strerror() fails to return a string for out-of-range
       dnl integers. Replace it.
       REPLACE_STRERROR=1
@@ -48,7 +39,40 @@
     ])
   else
     dnl The system's strerror() cannot know about the new errno values we add
-    dnl to <errno.h>. Replace it.
+    dnl to <errno.h>, or any fix for strerror(0). Replace it.
     REPLACE_STRERROR=1
   fi
 ])
+
+dnl Detect if strerror(0) passes (that is, does not set errno, and does not
+dnl return a string that matches strerror(-1)).
+AC_DEFUN([gl_FUNC_STRERROR_0],
+[
+  REPLACE_STRERROR_0=0
+  AC_CACHE_CHECK([whether strerror(0) succeeds],
+   [gl_cv_func_strerror_0_works],
+   [AC_RUN_IFELSE(
+      [AC_LANG_PROGRAM(
+         [[#include <string.h>
+           #include <errno.h>
+         ]],
+         [[int result = 0;
+           char *str;
+           errno = 0;
+           str = strerror (0);
+           if (!*str) result |= 1;
+           if (errno) result |= 2;
+           if (strstr (str, "nknown") || strstr (str, "ndefined"))
+             result |= 4;
+           return result;]])],
+      [gl_cv_func_strerror_0_works=yes],
+      [gl_cv_func_strerror_0_works=no],
+      [dnl Be pessimistic on cross-compiles for now.
+       gl_cv_func_strerror_0_works="guessing no"])
+  ])
+  if test "$gl_cv_func_strerror_0_works" != yes; then
+    REPLACE_STRERROR_0=1
+    AC_DEFINE([REPLACE_STRERROR_0], [1], [Define to 1 if strerror(0)
+      does not return a message implying success.])
+  fi
+])

--- a/m4/strerror_r.m4
+++ b/m4/strerror_r.m4
@@ -1,4 +1,4 @@
-# strerror_r.m4 serial 11
+# strerror_r.m4 serial 12
 dnl Copyright (C) 2002, 2007-2011 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -20,7 +20,7 @@
   fi
 
   if test $ac_cv_func_strerror_r = yes; then
-    if test -z "$ERRNO_H"; then
+    if test "$ERRNO_H:$REPLACE_STRERROR_0" = :0; then
       if test $gl_cv_func_strerror_r_posix_signature = yes; then
         case "$gl_cv_func_strerror_r_works" in
           dnl The system's strerror_r has bugs.  Replace it.
@@ -32,7 +32,7 @@
       fi
     else
       dnl The system's strerror_r() cannot know about the new errno values we
-      dnl add to <errno.h>. Replace it.
+      dnl add to <errno.h>, or any fix for strerror(0). Replace it.
       REPLACE_STRERROR_R=1
     fi
   fi
@@ -41,7 +41,7 @@
 # Prerequisites of lib/strerror_r.c.
 AC_DEFUN([gl_PREREQ_STRERROR_R], [
   dnl glibc >= 2.3.4 and cygwin 1.7.9 have a function __xpg_strerror_r.
-  AC_CHECK_FUNCS([__xpg_strerror_r])
+  AC_CHECK_FUNCS_ONCE([__xpg_strerror_r])
   AC_CHECK_FUNCS_ONCE([catgets])
 ])
 
@@ -51,10 +51,11 @@
 [
   AC_REQUIRE([gl_HEADER_ERRNO_H])
   AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_REQUIRE([gl_FUNC_STRERROR_0])
 
   AC_CHECK_FUNCS_ONCE([strerror_r])
   if test $ac_cv_func_strerror_r = yes; then
-    if test -z "$ERRNO_H"; then
+    if test "$ERRNO_H:$REPLACE_STRERROR_0" = :0; then
       dnl The POSIX prototype is:  int strerror_r (int, char *, size_t);
       dnl glibc, Cygwin:           char *strerror_r (int, char *, size_t);
       dnl AIX 5.1, OSF/1 5.1:      int strerror_r (int, char *, int);
@@ -116,8 +117,8 @@
                 aix*)  gl_cv_func_strerror_r_works="guessing no";;
                        # Guess no on HP-UX.
                 hpux*) gl_cv_func_strerror_r_works="guessing no";;
-                       # Guess no on FreeBSD.
-                freebsd*)  gl_cv_func_strerror_r_works="guessing no";;
+                       # Guess no on BSD variants.
+                *bsd*)  gl_cv_func_strerror_r_works="guessing no";;
                        # Guess yes otherwise.
                 *)     gl_cv_func_strerror_r_works="guessing yes";;
               esac
@@ -127,7 +128,7 @@
       else
         dnl The system's strerror() has a wrong signature.
         dnl glibc >= 2.3.4 and cygwin 1.7.9 have a function __xpg_strerror_r.
-        AC_CHECK_FUNCS([__xpg_strerror_r])
+        AC_CHECK_FUNCS_ONCE([__xpg_strerror_r])
         dnl In glibc < 2.14, __xpg_strerror_r does not populate buf on failure.
         dnl In cygwin < 1.7.10, __xpg_strerror_r clobbers strerror's buffer.
         if test $ac_cv_func___xpg_strerror_r = yes; then

--- a/modules/strerror-override
+++ b/modules/strerror-override
@@ -5,13 +5,15 @@
 lib/strerror-override.h
 lib/strerror-override.c
 m4/sys_socket_h.m4
+m4/strerror.m4
 
 Depends-on:
 errno
 
 configure.ac:
 AC_REQUIRE([gl_HEADER_ERRNO_H])
-if test -n "$ERRNO_H"; then
+AC_REQUIRE([gl_FUNC_STRERROR_0])
+if test -n "$ERRNO_H" || test $REPLACE_STRERROR_0 = 1; then
   AC_LIBOBJ([strerror-override])
   gl_PREREQ_SYS_H_WINSOCK2
 fi