tools/nolibc: add getopt()

Introduce a getopt() implementation based on the one from musl.
The only deviations are adaption to the kernel coding style and nolibc
infrastructure and removal of multi-byte support.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Willy Tarreau <w@1wt.eu>

tools/include/nolibc/Makefile

@@ -33,6 +33,7 @@ all_files := \
 		elf.h \
 		errno.h \
 		fcntl.h \
+		getopt.h \
 		limits.h \
 		nolibc.h \
 		signal.h \

tools/include/nolibc/getopt.h

@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * getopt function definitions for NOLIBC, adapted from musl libc
+ * Copyright (C) 2005-2020 Rich Felker, et al.
+ * Copyright (C) 2025 Thomas Weißschuh <linux@weissschuh.net>
+ */
+
+#ifndef _NOLIBC_GETOPT_H
+#define _NOLIBC_GETOPT_H
+
+struct FILE;
+static struct FILE *const stderr;
+static int fprintf(struct FILE *stream, const char *fmt, ...);
+
+__attribute__((weak,unused,section(".data.nolibc_getopt")))
+char *optarg;
+
+__attribute__((weak,unused,section(".data.nolibc_getopt")))
+int optind = 1, opterr = 1, optopt;
+
+static __attribute__((unused))
+int getopt(int argc, char * const argv[], const char *optstring)
+{
+	static int __optpos;
+	int i;
+	char c, d;
+	char *optchar;
+
+	if (!optind) {
+		__optpos = 0;
+		optind = 1;
+	}
+
+	if (optind >= argc || !argv[optind])
+		return -1;
+
+	if (argv[optind][0] != '-') {
+		if (optstring[0] == '-') {
+			optarg = argv[optind++];
+			return 1;
+		}
+		return -1;
+	}
+
+	if (!argv[optind][1])
+		return -1;
+
+	if (argv[optind][1] == '-' && !argv[optind][2])
+		return optind++, -1;
+
+	if (!__optpos)
+		__optpos++;
+	c = argv[optind][__optpos];
+	optchar = argv[optind] + __optpos;
+	__optpos++;
+
+	if (!argv[optind][__optpos]) {
+		optind++;
+		__optpos = 0;
+	}
+
+	if (optstring[0] == '-' || optstring[0] == '+')
+		optstring++;
+
+	i = 0;
+	d = 0;
+	do {
+		d = optstring[i++];
+	} while (d && d != c);
+
+	if (d != c || c == ':') {
+		optopt = c;
+		if (optstring[0] != ':' && opterr)
+			fprintf(stderr, "%s: unrecognized option: %c\n", argv[0], *optchar);
+		return '?';
+	}
+	if (optstring[i] == ':') {
+		optarg = 0;
+		if (optstring[i + 1] != ':' || __optpos) {
+			optarg = argv[optind++];
+			if (__optpos)
+				optarg += __optpos;
+			__optpos = 0;
+		}
+		if (optind > argc) {
+			optopt = c;
+			if (optstring[0] == ':')
+				return ':';
+			if (opterr)
+				fprintf(stderr, "%s: option requires argument: %c\n",
+					argv[0], *optchar);
+			return '?';
+		}
+	}
+	return c;
+}
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#endif /* _NOLIBC_GETOPT_H */

tools/include/nolibc/nolibc.h

@@ -113,6 +113,7 @@
 #include "stackprotector.h"
 #include "dirent.h"
 #include "fcntl.h"
+#include "getopt.h"
 
 /* Used by programs to avoid std includes */
 #define NOLIBC