Rule for ejudge.sh; fix declaration of video_memory.

Makefile

@@ -17,6 +17,10 @@ run: image.bin
 run-nox: image.bin
 	qemu-system-i386 -nographic -drive format=raw,file=$< -serial mon:stdio
 
+ejudge.sh: image.bin
+	echo >$@ "#!/bin/sh\nexec qemu-system-i386 -nographic -drive format=raw,file=$< -serial mon:stdio"
+	chmod +x $@
+
 debug-boot-nox: image.bin mbr.elf
 	qemu-system-i386 -nographic -drive format=raw,file=$< -s -S &
 	$(GDB) mbr.elf \

drivers/vga.c

@@ -1,6 +1,8 @@
 #include "port.h"
 #include "vga.h"
 
+char* const video_memory = (char*) 0xb8000;
+
 static unsigned char get_color(unsigned char fg, unsigned char bg) {
     return (bg << 4) + fg;
 }

drivers/vga.h

@@ -1,6 +1,6 @@
 #pragma once
 
-static char* const video_memory = (char*) 0xb8000;
+extern char* const video_memory;
 
 enum {
     ROWS = 25,