Lab 2 Report - PROCESSING TEXT IN ASSEMBLY LANGUAGE

Name	ID
Mo'men Ahmed	2200768
John Sameh	2200414

1. Compiling the code

2. Using simulation instead of physical board

3. Running the program till start of main using a breakpoint

Register	Value
R13 (SP)	`0x20000660`
R14 (LR)	`0x08000233`
R15 (PC)	`0x08000314`

4. Start of program in disassembly

Instruction: 0x08000314 B580 PUSH {r7,lr}.
Interpretation: The same as the program counter (PC).

5. Instruction execution

Registers changed: R13 (SP), R15 (PC).
Relation with instruction:

SP was reduced by 2 to (from 0x20000660 to 0x20000658) because two register values were pushed to the stack.
The PC was increased by 2 because the difference between each two instructions is two.

6. Finding first 4-byte long instructions

7. Finding values of some registers before executing `my_strcpy`

Register	Value
R13 (SP)	`0x20000628`
R14 (LR)	`0x08000233`
R15 (PC)	`0x08000344`

8. Executing `my_strcpy` function

Register	Value
R13 (SP)	`0x20000628`
R14 (LR)	`0x08000349`
R15 (PC)	`0x08000374`
The LR was changed to point to the new location to be returned to. The PC was changed to the new instruction address matching the disassembly window.

9. Registers holding `my_strcpy` arguments

Argument	Register	Value
`src_ptr`	R0 `0x20000644`	"Hello, world!"
`dst_ptr`	R1 `0x08000630`	""

10. Viewing values of arguments in memory using Memory Windows

11 and 12. Content

Argument	Content
`src_ptr`	Hello, world!
`dst_ptr`	.

13.

Register	Function
R0	Points to the character to be copied
R2	Holds the character copied
R1	Character is pasted here

14. Values before stepping out of the function

Register	Value
R13 (SP)	`0x20000620`
R14 (LR)	`0x08000349`
R15 (PC)	`0x08000386`

15. PC after stepping out of the function

R15 (PC): 0x08000348

16. Relationship between previous LR and PC

They are equal. The program returned to the point in main before entering the function.

17. Verifying `my_capitalize`