tools/nolibc: add stdarg.h header

This allows nolic to work with `-nostdinc` avoiding any reliance on
system headers.

The implementation has been lifted from musl libc 1.2.4.
There is already an implementation of stdarg.h in include/linux/stdarg.h
but that is GPL licensed and therefore not suitable for nolibc.

The used compiler builtins have been validated to be at least available
since GCC 4.1.2 and clang 3.0.0.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>

tools/include/nolibc/Makefile

@@ -34,6 +34,7 @@ all_files := \
 		signal.h \
 		stackprotector.h \
 		std.h \
+		stdarg.h \
 		stdint.h \
 		stdlib.h \
 		string.h \

tools/include/nolibc/nolibc.h

@@ -74,10 +74,10 @@
  *            -I../nolibc -o hello hello.c -lgcc
  *
  * The available standard (but limited) include files are:
- *   ctype.h, errno.h, signal.h, stdio.h, stdlib.h, string.h, time.h
+ *   ctype.h, errno.h, signal.h, stdarg.h, stdio.h, stdlib.h, string.h, time.h
  *
  * In addition, the following ones are expected to be provided by the compiler:
- *   float.h, stdarg.h, stddef.h
+ *   float.h, stddef.h
  *
  * The following ones which are part to the C standard are not provided:
  *   assert.h, locale.h, math.h, setjmp.h, limits.h

tools/include/nolibc/stdarg.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
+/*
+ * Variadic argument support for NOLIBC
+ * Copyright (C) 2005-2020 Rich Felker, et al.
+ */
+
+#ifndef _NOLIBC_STDARG_H
+#define _NOLIBC_STDARG_H
+
+typedef __builtin_va_list va_list;
+#define va_start(v, l)   __builtin_va_start(v, l)
+#define va_end(v)        __builtin_va_end(v)
+#define va_arg(v, l)     __builtin_va_arg(v, l)
+#define va_copy(d, s)    __builtin_va_copy(d, s)
+
+#endif /* _NOLIBC_STDARG_H */

tools/include/nolibc/stdio.h

@@ -7,13 +7,12 @@
 #ifndef _NOLIBC_STDIO_H
 #define _NOLIBC_STDIO_H
 
-#include <stdarg.h>
-
 #include "std.h"
 #include "arch.h"
 #include "errno.h"
 #include "types.h"
 #include "sys.h"
+#include "stdarg.h"
 #include "stdlib.h"
 #include "string.h"
 

tools/include/nolibc/sys.h

@@ -7,7 +7,6 @@
 #ifndef _NOLIBC_SYS_H
 #define _NOLIBC_SYS_H
 
-#include <stdarg.h>
 #include "std.h"
 
 /* system includes */
@@ -25,6 +24,7 @@
 
 #include "arch.h"
 #include "errno.h"
+#include "stdarg.h"
 #include "types.h"