How to write ARMGNU assembly code to write C = A + B?

Question

Here is my ARM assembly list file. I am suppose to write the assembly code to calculate: C = A + B; When I 'make all' I am getting the following error:

Error: undefined symbol r5 used as an immediate value

Error: undefined symbol r6 used as an immediate value

I am new to assembly files so I am kinda lost. what should I change in my .text section to get the errors away. I also was told to "Use a single point of addressability (DS) for the three memory accesses. Each memory access should use calculated offsets using labels (no hardcoded literal offset values)."

   SET_TARGET

  .text
  
  FUNCTION main,global

    push {r4,r5,r6,r7,lr}


      ldr  r4,=C //Store symbol C inside r4
      ldrb r5,=A //Store symbol C inside r4
      ldrh r6,=B //Store symbol C inside r4
      add  r4,r5 //Add A to C
      add  r4,r6 //Add B to C as well
    all_done: 

    pop {r4,r5,r6,r7,lr}
  
      bx lr

  ENDFUNC main

  .data

      .org 234
      .align 2,0xa5   

DS:    .word    0xbbbbbbbb

A:    .byte     123

      .align    1,0xa5
B:    .short    47587

      .align    2,0xa5
C:    .word     ~0
      .align    3,0xa5
      .word 0xeeeeeeee

  .end

Answer 1

gnu assembler:

so.s: Assembler messages:
so.s:1: Error: bad instruction `set_target'
so.s:5: Error: bad instruction `function main,global'
so.s:21: Error: bad instruction `endfunc main'

These are of course not gnu assembler directives they look like ARM/Kiel type of a thing.

cleaned up it looks something like this

.text

.type main, %function
.globl main
main:

    push {r4,r5,r6,r7}

    ldr  r4,=C @ copy address of C to r4
    ldrb r5,=A @ copy address of A to r5
    ldrh r6,=B @ copy address of B to r6
    add  r4,r5 @ &C = &C + &A, r4 = address of C plus address of A
    add  r4,r6 @ &C = &C + &B, r4 = r4 plus address of B

    pop {r4,r5,r6,r7}

    bx lr

.data

      .align
A:    .byte     123

      .align
B:    .short    47587

      .align
C:    .word     ~0

For gnu assembler but based on your error messages it appears you are not using gnu assembler but something else. Assembly is specific to the tool not the target, so you need to write assembly language for the assembler you are using (ARM, Kiel, gas, etc).

And for that assembly language then you need to know the syntax. Very likely you don't want to add the addresses of the variables together but their values.

And did you want to return anything from this function?