Rearrange strerror() so that its itoa procedure can be used with

strerror_r().  Doing this allows us to ensure that strerror_r() always
fills the supplied buffer regardless of EINVAL or ERANGE errors.

strerror()'s semantics have changed slightly such that an argument of
0 is now considered invalid and errno is set to EINVAL.

Remove internal regression test for strerror() and strerror_r().  This
will be reincarnated in src/tools/regression/lib/libc/string.

In strerror(3), add a comment about strerror()'s bogus return type.

PR:	44356

lib/libc/string/strerror.3

@@ -115,7 +115,7 @@ leaves
 unchanged and returns
 .Er EINVAL .
 Error numbers recognized by this implementation fall in
-the range 0 \(<=
+the range 0 \(<
 .Fa errnum
 <
 .Fa sys_nerr .
@@ -169,6 +169,11 @@ For unknown error numbers, the
 function will return its result in a static buffer which
 may be overwritten by subsequent calls.
 .Pp
+The return type for
+.Fn strerror
+is missing a type-qualifier; it should actually be
+.Vt const char * .
+.Pp
 The
 .Fn perror
 function is implemented in terms of

lib/libc/string/strerror.c

@@ -37,108 +37,62 @@ static char sccsid[] = "@(#)strerror.c	8.1 (Berkeley) 6/4/93";
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <errno.h>
 #include <stdio.h>
 #include <string.h>
-#include <errno.h>
 
-int
-strerror_r(int errnum, char *strerrbuf, size_t buflen)
+#define	UPREFIX		"Unknown error: "
+/*
+ * Define a buffer size big enough to describe a 64-bit signed integer
+ * converted to ASCII decimal (19 bytes), with an optional leading sign
+ * (1 byte), finally we get the prefix and a trailing NUL from UPREFIX.
+ */
+#define	EBUFSIZE	(20 + sizeof(UPREFIX))
+
+/* Don't link to stdio(3) to avoid bloat for statically linked binaries. */
+static void
+errstr(int num, char *buf, size_t len)
 {
-	int             len;
+	unsigned int uerr;
+	char *p, *t;
+	char tmp[EBUFSIZE];
 
-	if ((errnum >= 0) && (errnum < sys_nerr)) {
-		len = strlcpy(strerrbuf, (char *)sys_errlist[errnum], buflen);
-		return ((len < buflen) ? 0 : ERANGE);
-	}
-	return (EINVAL);
-}
-
-char *
-strerror(num)
-	int             num;
-{
-	char           *p, *t;
-	unsigned int	uerr;
-	static char const unknown_prefix[] = "Unknown error: ";
-
-	/*
-	 * Define a buffer size big enough to describe a 64-bit
-	 * number in ASCII decimal (19), with optional leading sign
-	 * (+1) and trailing NUL (+1).
-	 */
-#       define		NUMLEN 21
-#	define		EBUFLEN (sizeof unknown_prefix + NUMLEN)
-	char            tmp[NUMLEN];	/* temporary number */
-	static char     ebuf[EBUFLEN];	/* error message */
-
-	if ((num >= 0) && (num < sys_nerr))
-		return ((char *)sys_errlist[num]);
-
-	/*
-	 * Set errno to EINVAL per P1003.1-200x Draft June 14, 2001.
-	 */
-	errno = EINVAL;
-
-	/*
-	 * Print unknown errno by hand so we don't link to stdio(3).
-	 * This collects the ASCII digits in reverse order.
-	 */
-	uerr = (num > 0) ? num : -num;
+	if (strlcpy(buf, UPREFIX, len) >= len)
+		return;
 	t = tmp;
+	uerr = (num >= 0) ? num : -num;
 	do {
 		*t++ = "0123456789"[uerr % 10];
 	} while (uerr /= 10);
 	if (num < 0)
 		*t++ = '-';
-
-	/*
-	 * Copy the "unknown" message and the number into the caller
-	 * supplied buffer, inverting the number string.
-	 */
-	strcpy(ebuf, unknown_prefix);
-	for (p = ebuf + sizeof unknown_prefix - 1; t > tmp; )
+	for (p = buf + strlen(UPREFIX); t > tmp && p < buf + len - 1;)
 		*p++ = *--t;
 	*p = '\0';
+}
+
+int
+strerror_r(int errnum, char *strerrbuf, size_t buflen)
+{
+	int retval;
+
+	retval = 0;
+	if (errnum < 1 || errnum >= sys_nerr) {
+		errstr(errnum, strerrbuf, buflen);
+		retval = EINVAL;
+	} else if (strlcpy(strerrbuf, sys_errlist[errnum], buflen) >= buflen)
+		retval = ERANGE;
+	return (retval);
+}
+
+char *
+strerror(int num)
+{
+	static char ebuf[EBUFSIZE];
+
+	if (num > 0 && num < sys_nerr)
+		return ((char *)sys_errlist[num]);
+	errno = EINVAL;
+	errstr(num, ebuf, sizeof(ebuf));
 	return (ebuf);
 }
-
-#ifdef STANDALONE_TEST
-
-#include <limits.h>
-
-main()
-{
-	char            mybuf[64];
-	int             ret;
-
-	errno = 0;
-
-	printf("strerror(0) yeilds: %s\n", strerror(0));
-	printf("strerror(1) yeilds: %s\n", strerror(1));
-	printf("strerror(47) yeilds: %s\n", strerror(47));
-	printf("strerror(sys_nerr - 1) yeilds: %s\n", strerror(sys_nerr - 1));
-	printf("errno = %d\n", errno); errno = 0;
-
-	printf("strerror(sys_nerr) yeilds: %s\n", strerror(sys_nerr));
-	printf("errno = %d\n", errno);  errno = 0;
-
-	printf("strerror(437) yeilds: %s\n", strerror(437));
-	printf("errno = %d\n", errno);  errno = 0;
-
-	printf("strerror(LONG_MAX) yeilds: %s\n", strerror(LONG_MAX));
-	printf("strerror(LONG_MIN) yeilds: %s\n", strerror(LONG_MIN));
-	printf("strerror(ULONG_MAX) yeilds: %s\n", strerror(ULONG_MAX));
-
-	memset(mybuf, '*', 63); mybuf[63] = '\0';
-	strerror_r(11, mybuf, 64);
-	printf("strerror_r(11) yeilds: %s\n", mybuf);
-
-	memset(mybuf, '*', 63); mybuf[63] = '\0';
-	ret = strerror_r(1234, mybuf, 64);
-	printf("strerror_r(1234) returns %d (%s)\n", ret, mybuf);
-
-	memset(mybuf, '*', 63); mybuf[63] = '\0';
-	ret = strerror_r(1, mybuf, 10);
-	printf("strerror_r on short buffer returns %d (%s)\n", ret, mybuf);
-}
-#endif