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ITEC 352
Lecture 19Functions in Assembly
Functions + Assembly
Review
• Questions?• Project due on Friday• Stacks• Function activation / deactivation
Functions + Assembly
Outline
• Functions in assembly• Intro to JVM
Functions + Assembly
Activation record
• An activation record is the memory allocated for each function activation. It contains the following data:
return address
memory for each local variable.
memory for parameter values passed from caller function
memory addresses of dynamically allocated memory.
Functions + Assembly
Step 1
• Consider a program:1. int f( int x, int y) {2. int a = 10; 3. int b = 5;4. }5. int main() {6. int z = 5; 7. f(z, z) ; 8. }
Initially the stack is empty.
Execution of this program starts with the function main. Hence, an activation record for main is created as shown on the stack.
PROGRAM STACK
Return address
Activation record for main. Memory for z
Stack pointer (%sp)
Functions + Assembly
Step 2
• Consider a program:1. int f( int x, int y) {2. int a = 10; 3. int b = 5;4. }5. int main() {6. int z = 5; 7. f(z, z) ; 8. }
Next: The function “f” is invoked. We have to create and then push the activation record of “f”. However, before we do that, we have to create space for the actual parameters that we want to pass to function f (here it is z, z)
PROGRAM STACK
Return address
Parameters to be passed to f.
Memory for z
Stack pointer (%sp)
5
5
return addressIn ARC this is stored in %r15 (address of line 8)
Functions + Assembly
Step 2B
• Consider a program:1. int f( int x, int y) {2. int a = 10; 3. int b = 5;4. }5. int main() {6. int z = 5; 7. f(z, z) ; 8. }
Next: This is a continuation from previous slide. You can see that we now have the complete activation record of function f.
PROGRAM STACK
Return address
Activation record of function f.
Memory for z
Stack pointer (%sp)
5
5
return address(%r15)
a (value 10)
b (value 5)
Functions + Assembly
Final step
• Consider a program:1. int f( int x, int y) {2. int a = 10; 3. int b = 5;4. }5. int main() {6. int z = 5; 7. f(z, z) ; 8. }
Next: After f finishes execution its activation record is no longer “live” -- it is popped out.
PROGRAM STACK
Return address
Program stack after f has finished execution. You can see that the local variables a and b are no longer accessible,
Memory for z
Stack pointer (%sp)
Functions + Assembly
Functions + Assembly
Using stacks: in assembly language
Stack pointer is stored in register %r14
A stack grows from high memory region to low memory region. Hence, when we push parameters onto the stack, we subtract a word from
the current stack pointer to update its value.
Functions + Assembly
I/O in Assembly
• Based on what you studied so far, how do you think I/O must be done in architecture? – E.g., how can a program read from, say
a touchscreen?
Functions + Assembly
I/O in Assembly
• Two choices: – Use special instructions to access each
I/O device.• Any disadvantages?
– Use memory mapped I/O.• What is memory mapped I/O?
Functions + Assembly
Memory mapped I/O
• Devices are accessed as if they are memory locations. – Devices occupy sections of the address space where no other
memory exists.
0216
217
219
222
223 -4
Reserved for BIOS
Add in Video Memory #1
Add in Video Memory #2
Unused
Working memory
System Stack
Screen flash Touchscreen x Touchscreen y
224 -4
Stack Pointer
I/O Space
Functions + Assembly
Next:
• Example of assembly in the Java Virtual machine
Functions + Assembly
Java Virtual Machine Architecture
Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring
Functions + Assembly
Functions + Assembly
A Java Class File
Functions + Assembly
Review
• Functions in assembly• Intro to JVM + Bytecode
