32-bit ARM Assembly

Registers

• R0 GPR (General Purpose Register)

• R1 GPR (General Purpose Register)

• R2 GPR (General Purpose Register)
  ...

• R11 GPR (General Purpose Register)

• R12 GPR (General Purpose Register)

• R13 Stack Pointer

• R14 Link Register

• R15 Program Counter - Is responsible for directing the CPU to what instruction will be executed next.

  # Control the PC directly (not recommended in User mode.)
  mov r15, 0x00000000
  
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• CPSR (Current Program Status Register) - Stores information about the program and the results of a particular operation.

Create Assembly Program

@ LR Demo - Link Register Demo

	.global __start

__start:
	mov r7, #0x30   @ mov hex 30 into r7
	b no_return     @ branch to no_return function which never returns

no_return:
	mov r7, #1      @ mov decimal 1 into r7
	bl my_function  @ go to my_function which after execution

wrap_up:
	mov r7, #0x12   @ mov hex 12 into r7
	b exit          @ branch to exit

my_function:
	mov r0, #10     @ mov decimal 10 into r0
	mov pc, lr      @ mov the ret address into the program counter

exit:
	mov r7, #1      @ sys_exit
  	svc 0

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To compile it, run the following commands.

as -o sample.o sample.s
ld -o sample sample.o

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