tools/nolibc: add err.h

Add a few convenient helpers to print error and warning messages.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260318-nolibc-err-h-v4-2-08247a694bd9@weissschuh.net

3 files changed, 89 insertions, 0 deletions

diff --git a/tools/include/nolibc/Makefile b/tools/include/nolibc/Makefile
index 1958dda98895..5d242312943f 100644
--- a/tools/include/nolibc/Makefile
+++ b/tools/include/nolibc/Makefile
@@ -30,6 +30,7 @@ all_files := \
 		ctype.h \
 		dirent.h \
 		elf.h \
+		err.h \
 		errno.h \
 		fcntl.h \
 		getopt.h \
diff --git a/tools/include/nolibc/err.h b/tools/include/nolibc/err.h
new file mode 100644
index 000000000000..e22ae87a7289
--- /dev/null
+++ b/tools/include/nolibc/err.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * formatted error message for NOLIBC
+ * Copyright (C) 2026 Thomas Weißschuh <linux@weissschuh.net>
+ */
+
+/* make sure to include all global symbols */
+#include "nolibc.h"
+
+#ifndef _NOLIBC_ERR_H
+#define _NOLIBC_ERR_H
+
+#include "errno.h"
+#include "stdarg.h"
+#include "sys.h"
+
+static __attribute__((unused))
+void vwarn(const char *fmt, va_list args)
+{
+	fprintf(stderr, "%s: ", program_invocation_short_name);
+	vfprintf(stderr, fmt, args);
+	fprintf(stderr, ": %m\n");
+}
+
+static __attribute__((unused))
+void vwarnx(const char *fmt, va_list args)
+{
+	fprintf(stderr, "%s: ", program_invocation_short_name);
+	vfprintf(stderr, fmt, args);
+	fprintf(stderr, "\n");
+}
+
+static __attribute__((unused))
+void warn(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vwarn(fmt, args);
+	va_end(args);
+}
+
+static __attribute__((unused))
+void warnx(const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	vwarnx(fmt, args);
+	va_end(args);
+}
+
+static __attribute__((noreturn, unused))
+void verr(int eval, const char *fmt, va_list args)
+{
+	vwarn(fmt, args);
+	exit(eval);
+}
+
+static __attribute__((noreturn, unused))
+void verrx(int eval, const char *fmt, va_list args)
+{
+	warnx(fmt, args);
+	exit(eval);
+}
+
+static __attribute__((noreturn, unused))
+void err(int eval, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	verr(eval, fmt, args);
+	va_end(args);
+}
+
+static __attribute__((noreturn, unused))
+void errx(int eval, const char *fmt, ...)
+{
+	va_list args;
+
+	va_start(args, fmt);
+	verrx(eval, fmt, args);
+	va_end(args);
+}
+
+#endif /* _NOLIBC_ERR_H */
diff --git a/tools/include/nolibc/nolibc.h b/tools/include/nolibc/nolibc.h
index d1d08b7f8599..fe8195483b6d 100644
--- a/tools/include/nolibc/nolibc.h
+++ b/tools/include/nolibc/nolibc.h
@@ -130,6 +130,7 @@
 #include "getopt.h"
 #include "poll.h"
 #include "math.h"
+#include "err.h"
 
 /* Used by programs to avoid std includes */
 #define NOLIBC