fix main return type

Makefile

@@ -48,7 +48,7 @@ kernel : $(OBJS) bootother.S user1 usertests userfs
 	$(LD) -N -e start -Ttext 0x7000 -o bootother.out bootother.o
 	$(OBJCOPY) -S -O binary bootother.out bootother
 	$(OBJDUMP) -S bootother.o > bootother.asm
-	$(LD) -Ttext 0x100000 -e main -o kernel $(OBJS) -b binary bootother user1 usertests userfs
+	$(LD) -Ttext 0x100000 -e main0 -o kernel $(OBJS) -b binary bootother user1 usertests userfs
 	$(OBJDUMP) -S kernel > kernel.asm
 
 vectors.S : vectors.pl

main.c

@@ -18,8 +18,11 @@ extern uint8_t _binary_userfs_start[], _binary_userfs_size[];
 extern int use_console_lock;
 
 // CPU 0 starts running C code here.
-int
-main()
+// This is called main0 not main so that it can have
+// a void return type.  Gcc can't handle functions named
+// main that don't return int.  Really.
+void
+main0(void)
 {
   int i;
   struct proc *p;
@@ -89,7 +92,7 @@ main()
 }
 
 // Additional processors start here.
-int 
+void
 mpmain(void)
 {
   cprintf("an application processor\n");