Add obstack_vprint function

closes void-linux#9

obstack.h

@@ -110,6 +110,7 @@
 
 #include <stddef.h>             /* For size_t and ptrdiff_t.  */
 #include <string.h>             /* For __GNU_LIBRARY__, and memcpy.  */
+#include <stdarg.h>             /* For va_list. */
 
 #if _OBSTACK_INTERFACE_VERSION == 1
 /* For binary compatibility with obstack version 1, which used "int"
@@ -213,6 +214,7 @@ extern _OBSTACK_SIZE_T _obstack_memory_used (struct obstack *)
 
 /* Declare obstack_printf; it's in obstack_printf.c. */
 extern int obstack_printf(struct obstack *obstack, const char *__restrict fmt, ...);
+extern int obstack_vprintf(struct obstack *obstack, const char *__restrict fmt, va_list args);
 
 
 /* Error handler called when 'obstack_chunk_alloc' failed to allocate

obstack_printf.c

@@ -1,18 +1,41 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <strings.h>
+#include <stdlib.h>
 #include "obstack.h"
 
 int obstack_printf(struct obstack *obstack, const char *__restrict fmt, ...)
 {
-	char buf[1024];
 	va_list ap;
 	int len;
 
 	va_start(ap, fmt);
-	len = vsnprintf(buf, sizeof(buf), fmt, ap);
-	obstack_grow(obstack, buf, len);
+	len = obstack_vprintf(obstack, fmt, ap);
 	va_end(ap);
 
 	return len;
 }
+
+
+int obstack_vprintf (struct obstack *obstack, const char *__restrict fmt, va_list args)
+{
+	char buf[1024];
+	size_t len;
+	char * str = buf;
+
+	len = vsnprintf (buf, sizeof(buf), fmt, args);
+	if (len >= sizeof(buf)) {
+		str = NULL;
+		len = vasprintf(&str, fmt, args);
+		if (len < 0) {
+			free(str);
+			return -1;
+		}
+	}
+	obstack_grow (obstack, str, len);
+
+	if (str != buf)
+		free(str);
+
+	return len;
+}