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.weisssc...@linutronix.de>
---
 tools/include/nolibc/Makefile |   1 +
 tools/include/nolibc/getopt.h | 105 ++++++++++++++++++++++++++++++++++++++++++
 tools/include/nolibc/nolibc.h |   1 +
 3 files changed, 107 insertions(+)

diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile
index 
dceec0e1a135119108d6f4dcb3d2ec57c002ffd3..821a716094549ff9ee2fbe006fb7b3066e5e418d
 100644
--- a/tools/include/nolibc/Makefile
+++ b/tools/include/nolibc/Makefile
@@ -31,6 +31,7 @@ all_files := \
                ctype.h \
                dirent.h \
                errno.h \
+               getopt.h \
                nolibc.h \
                signal.h \
                stackprotector.h \
diff --git a/tools/include/nolibc/getopt.h b/tools/include/nolibc/getopt.h
new file mode 100644
index 
0000000000000000000000000000000000000000..35aee582681b79e21bce8ddbf634ae9dfdef8f1d
--- /dev/null
+++ b/tools/include/nolibc/getopt.h
@@ -0,0 +1,105 @@
+/* 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 <li...@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;
+__attribute__((weak,unused,section(".data.nolibc_getopt")))
+int opterr = 1;
+__attribute__((weak,unused,section(".data.nolibc_getopt")))
+int optopt;
+__attribute__((weak,unused,section(".data.nolibc_getopt")))
+int __optpos;
+
+static __inline__
+int getopt(int argc, char * const argv[], const char *optstring)
+{
+       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 */
diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index 
05d92afedb7258f0e3c311bf6f12be68b25d6e9a..d4043051072928f43d4d73c0e509430087c66e94
 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -106,6 +106,7 @@
 #include "time.h"
 #include "stackprotector.h"
 #include "dirent.h"
+#include "getopt.h"
 
 /* Used by programs to avoid std includes */
 #define NOLIBC

-- 
2.48.1


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