SPRUI03E June 2015 – January 2023
These directives associate portions of an assembly language program with the appropriate sections:
Chapter 3 discusses these sections in detail.
The example that follows shows how you can use sections directives to associate code and data with the proper sections. This is an output listing; column 1 shows line numbers, and column 2 shows the SPC values. (Each section has its own program counter, or SPC.) When code is first placed in a section, its SPC equals 0. When you resume assembling into a section after other code is assembled, the section's SPC resumes counting as if there had been no intervening code.
The directives in this example perform the following tasks:
| .text | initializes words with the values 1, 2, 3, 4, 5, 6, 7, and 8. |
| .data | initializes words with the values 9, 10, 11, 12, 13, 14, 15, and 16. |
| var_defs | initializes words with the values 17 and 18. |
| .bss | reserves 19 bytes. |
| xy | reserves 20 bytes. |
The .bss and .usect directives do not end the current section or begin new sections; they reserve the specified amount of space, and then the assembler resumes assembling code or data into the current section.
00000004 00000002
6 00000008 00000003 .word 3,4
0000000c 00000004
7
8 **************************************************
9 * Start assembling into the .data section *
10 **************************************************
11 00000000 .data
12 00000000 00000009 .word 9, 10
00000004 0000000A
13 00000008 0000000B .word 11, 12
0000000c 0000000C
14
15 **************************************************
16 * Start assembling into a named, *
17 * initialized section, var_defs *
18 **************************************************
19 00000000 .sect "var_defs"
20 00000000 00000011 .word 17, 18
00000004 00000012
21
22 **************************************************
23 * Resume assembling into the .data section *
24 **************************************************
25 00000010 .data
26 00000010 0000000D .word 13, 14
00000014 0000000E
27 00000000 .bss sym, 19 ; Reserve space in .bss
28 00000018 0000000F .word 15, 16 ; Still in .data
0000001c 00000010
29
30 **************************************************
31 * Resume assembling into the .text section *
32 **************************************************
33 00000010 .text
34 00000010 00000005 .word 5, 6
00000014 00000006
35 00000000 usym .usect "xy", 20 ; Reserve space in xy
36 00000018 00000007 .word 7, 8 ; Still in .text
0000001c 00000008