4 files changed, 19 insertions, 11 deletions

diff --git a/lib/libc/gen/errlst.c b/lib/libc/gen/errlst.c
index b105cc80cf40b..d8178236deed9 100644
--- a/lib/libc/gen/errlst.c
+++ b/lib/libc/gen/errlst.c
@@ -36,7 +36,7 @@ __FBSDID("$FreeBSD$");
 #include <stdio.h>
 
 const char *const sys_errlist[] = {
-	"Undefined error: 0",			/*  0 - ENOERROR */
+	"No error: 0",				/*  0 - ENOERROR */
 	"Operation not permitted",		/*  1 - EPERM */
 	"No such file or directory",		/*  2 - ENOENT */
 	"No such process",			/*  3 - ESRCH */
diff --git a/lib/libc/string/strerror.3 b/lib/libc/string/strerror.3
index 2d6d206c10952..0ec6cb0af4062 100644
--- a/lib/libc/string/strerror.3
+++ b/lib/libc/string/strerror.3
@@ -32,7 +32,7 @@
 .\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
 .\" $FreeBSD$
 .\"
-.Dd October 12, 2004
+.Dd April 5, 2011
 .Dt STRERROR 3
 .Os
 .Sh NAME
@@ -114,6 +114,9 @@ the range 0 <
 .Fa errnum
 <
 .Fa sys_nerr .
+The number 0 is also recognized, although applications that take advantage of
+this are likely to use unspecified values of
+.Va errno .
 .Pp
 If insufficient storage is provided in
 .Fa strerrbuf
diff --git a/lib/libc/string/strerror.c b/lib/libc/string/strerror.c
index 890ed2139af82..57d253db46115 100644
--- a/lib/libc/string/strerror.c
+++ b/lib/libc/string/strerror.c
@@ -87,7 +87,7 @@ strerror_r(int errnum, char *strerrbuf, size_t buflen)
 	catd = catopen("libc", NL_CAT_LOCALE);
 #endif
 
-	if (errnum < 1 || errnum >= sys_nerr) {
+	if (errnum < 0 || errnum >= sys_nerr) {
 		errstr(errnum,
 #if defined(NLS)
 			catgets(catd, 1, 0xffff, UPREFIX),
diff --git a/tools/regression/lib/libc/string/test-strerror.c b/tools/regression/lib/libc/string/test-strerror.c
index f5274ed7f2271..ffc1633bab2f1 100644
--- a/tools/regression/lib/libc/string/test-strerror.c
+++ b/tools/regression/lib/libc/string/test-strerror.c
@@ -42,17 +42,12 @@ main(void)
 	char *sret;
 	int iret;
 
-	plan_tests(25);
+	plan_tests(27);
 
 	/*
 	 * strerror() failure tests.
 	 */
 	errno = 0;
-	sret = strerror(0);
-	ok1(strcmp(sret, "Unknown error: 0") == 0);
-	ok1(errno == EINVAL);
-
-	errno = 0;
 	sret = strerror(INT_MAX);
 	snprintf(buf, sizeof(buf), "Unknown error: %d", INT_MAX);
 	ok1(strcmp(sret, buf) == 0);
@@ -62,6 +57,11 @@ main(void)
 	 * strerror() success tests.
 	 */
 	errno = 0;
+	sret = strerror(0);
+	ok1(strcmp(sret, "No error: 0") == 0);
+	ok1(errno == 0);
+
+	errno = 0;
 	sret = strerror(EPERM);
 	ok1(strcmp(sret, "Operation not permitted") == 0);
 	ok1(errno == 0);
@@ -79,8 +79,8 @@ main(void)
 	 * strerror_r() failure tests.
 	 */
 	memset(buf, '*', sizeof(buf));
-	iret = strerror_r(0, buf, sizeof(buf));
-	ok1(strcmp(buf, "Unknown error: 0") == 0);
+	iret = strerror_r(-1, buf, sizeof(buf));
+	ok1(strcmp(buf, "Unknown error: -1") == 0);
 	ok1(iret == EINVAL);
 
 	memset(buf, '*', sizeof(buf));
@@ -117,6 +117,11 @@ main(void)
 	 * strerror_r() success tests.
 	 */
 	memset(buf, '*', sizeof(buf));
+	iret = strerror_r(0, buf, sizeof(buf));
+	ok1(strcmp(buf, "No error: 0") == 0);
+	ok1(iret == 0);
+
+	memset(buf, '*', sizeof(buf));
 	iret = strerror_r(EDEADLK, buf, sizeof(buf));
 	ok1(strcmp(buf, "Resource deadlock avoided") == 0);
 	ok1(iret == 0);