Initial version

code/test/start.S

@@ -0,0 +1,155 @@
+/* Start.s 
+ *	Assembly language assist for user programs running on top of Nachos.
+ *
+ *	Since we don't want to pull in the entire C library, we define
+ *	what we need for a user program here, namely Start and the system
+ *	calls.
+ */
+
+#include "syscall.h"
+
+/* -------------------------------------------------------------
+ * 0-jump catcher
+ *	Catch jumps to 0 by emiting an illegal instruction at 0
+ * -------------------------------------------------------------
+ */
+	.text   
+	.org 0
+	.long 0xffffffff
+	.long 0xffffffff
+
+/* -------------------------------------------------------------
+ * __start
+ *	Initialize running a C program, by calling "main". 
+ *
+ * 	NOTE: This has to be first, so that it gets loaded at location 0.
+ *	The Nachos kernel always starts a program by jumping to location 0.
+ * -------------------------------------------------------------
+ */
+
+	.org USER_START_ADDRESS
+
+	.globl __start
+	.ent	__start
+__start:
+	jal	main
+	move	$4,$0		
+	jal	Exit	 /* if we return from main, exit(0) */
+	.end __start
+
+/* -------------------------------------------------------------
+ * Exit-returning catcher
+ *	Catch Exit system call returning
+ * -------------------------------------------------------------
+ */
+	.long 0xffffffff
+	.long 0xffffffff
+
+/* -------------------------------------------------------------
+ * System call stubs:
+ *	Assembly language assist to make system calls to the Nachos kernel.
+ *	There is one stub per system call, that places the code for the
+ *	system call into register r2, and leaves the arguments to the
+ *	system call alone (in other words, arg1 is in r4, arg2 is 
+ *	in r5, arg3 is in r6, arg4 is in r7)
+ *
+ * 	The return value is in r2. This follows the standard C calling
+ * 	convention on the MIPS.
+ * -------------------------------------------------------------
+ */
+
+	.globl Halt
+	.ent	Halt
+Halt:
+	addiu $2,$0,SC_Halt
+	syscall
+	j	$31
+	.end Halt
+
+	.globl Exit
+	.ent	Exit
+Exit:
+	addiu $2,$0,SC_Exit
+	syscall
+	j	$31
+	.end Exit
+
+	.globl Exec
+	.ent	Exec
+Exec:
+	addiu $2,$0,SC_Exec
+	syscall
+	j	$31
+	.end Exec
+
+	.globl Join
+	.ent	Join
+Join:
+	addiu $2,$0,SC_Join
+	syscall
+	j	$31
+	.end Join
+
+	.globl Create
+	.ent	Create
+Create:
+	addiu $2,$0,SC_Create
+	syscall
+	j	$31
+	.end Create
+
+	.globl Open
+	.ent	Open
+Open:
+	addiu $2,$0,SC_Open
+	syscall
+	j	$31
+	.end Open
+
+	.globl Read
+	.ent	Read
+Read:
+	addiu $2,$0,SC_Read
+	syscall
+	j	$31
+	.end Read
+
+	.globl Write
+	.ent	Write
+Write:
+	addiu $2,$0,SC_Write
+	syscall
+	j	$31
+	.end Write
+
+	.globl Close
+	.ent	Close
+Close:
+	addiu $2,$0,SC_Close
+	syscall
+	j	$31
+	.end Close
+
+	.globl Fork
+	.ent	Fork
+Fork:
+	addiu $2,$0,SC_Fork
+	syscall
+	j	$31
+	.end Fork
+
+	.globl Yield
+	.ent	Yield
+Yield:
+	addiu $2,$0,SC_Yield
+	syscall
+	j	$31
+	.end Yield
+
+/* dummy function to keep gcc happy */
+        .globl  __main
+        .ent    __main
+__main:
+        j       $31
+        .end    __main
+