Section 11.6 Assembler Listings
Most assemblers can provide the programmer with a listing file, which shows the machine code for each instruction. The command line option for the as assembler to produce an assembly listing is -al. This causes the listing to be printed to standard output (your terminal window), so you probably want to redirect this output to a file. For example, the command:
as --gstabs -al -o assignment2.o assignment2.s > assignment2.lst
produces the listing file shown in Listing 11.6.1.
ARM GAS assignment2.s page 1
1 @ assignment2.s
2 @ Assignment three ways.
3 @ 2017-09-29: Bob Plantz
4
5 @ Define my Raspberry Pi
6 .cpu cortex-a53
7 .fpu neon-fp-armv8
8 .syntax unified @ modern syntax
9
10 @ Useful source code constants
11 .equ z,-16
12 .equ local,8
13
14 @ Constant program data
15 .section .rodata
16 .align 2
17 formatMsg:
18 0000 2569202B .asciz "%i + %i = %i\n"
18 20256920
18 3D202569
18 0A00
19
20 @ Program code
21 .text
22 .align 2
23 .global main
24 .type main, %function
25 main:
26 0000 0CD04DE2 sub sp, sp, 12 @ space for saving regs
27 0004 00B08DE5 str fp, [sp, 0] @ save fp
28 0008 04E08DE5 str lr, [sp, 4] @ lr
29 000c 08508DE5 str r5, [sp, 8] @ r5
30 0010 0C408DE5 str r4, [sp, 12] @ and r4
31 0014 0CB08DE2 add fp, sp, 12 @ our frame pointer
32 0018 08D04DE2 sub sp, sp, local @ allocate memory for local var
33
34 001c 7B50A0E3 mov r5, 123 @ x = 123;
35 0020 38409FE5 ldr r4, yValue @ y = 4567;
36 0024 043085E0 add r3, r5, r4 @ x + y
37 0028 10300BE5 str r3, [fp, z] @ z = x + y;
38
39 002c 30009FE5 ldr r0, formatMsgAddr @ printf("%i + %i = %i\n",
40 0030 0510A0E1 mov r1, r5 @ x,
41 0034 0420A0E1 mov r2, r4 @ y,
42 0038 10301BE5 ldr r3, [fp, z] @ z);
43 003c FEFFFFEB bl printf
44
45 0040 0000A0E3 mov r0, 0 @ return 0;
46 0044 08D08DE2 add sp, sp, local @ deallocate local var
47 0048 00B09DE5 ldr fp, [sp, 0] @ restore fp
48 004c 04E09DE5 ldr lr, [sp, 4] @ lr
49 0050 08509DE5 ldr r5, [sp, 8] @ r5
50 0054 0C409DE5 ldr r4, [sp, 12] @ r4
51 0058 0CD08DE2 add sp, sp, 12 @ and sp
52 005c 1EFF2FE1 bx lr @ return
53
54 .align 2
ARM GAS assignment2.s page 2
55 yValue:
56 0060 D7110000 .word 4567
57 formatMsgAddr:
58 0064 00000000 .word formatMsg
59
The first column is the line number. The next column is the address, relative to the beginning of this function. The third column, the 32-bit numbers, is the machine code. Be careful to remember that the machine code is shown in byte order not word order and that the ARM in the Raspberry Pi uses little endian memory storage.