sandbox: add function os_printf()

Before setting up the devices U-Boot's printf() function cannot be used
for console output. Provide function os_printf() to print to stderr.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

arch/sandbox/cpu/os.c

@@ -12,6 +12,7 @@
 #include <getopt.h>
 #include <setjmp.h>
 #include <signal.h>
+#include <stdarg.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -54,6 +55,18 @@ ssize_t os_write(int fd, const void *buf, size_t count)
 	return write(fd, buf, count);
 }
 
+int os_printf(const char *fmt, ...)
+{
+	va_list args;
+	int i;
+
+	va_start(args, fmt);
+	i = vfprintf(stdout, fmt, args);
+	va_end(args);
+
+	return i;
+}
+
 off_t os_lseek(int fd, off_t offset, int whence)
 {
 	if (whence == OS_SEEK_SET)

include/os.h

@@ -16,6 +16,13 @@
 struct rtc_time;
 struct sandbox_state;
 
+/**
+ * os_printf() - print directly to OS console
+ *
+ * @format: format string
+ */
+int os_printf(const char *format, ...);
+
 /**
  * Access to the OS read() system call
  *