MIPS-Assembly: How to 'define' subroutine for later use

Question

There are tons of great examples on how to properly follow MIPS function calling conventions. However, I'm getting stuck on how to use a function only when 'called'. The following will print 51 (using MARS):

.data
strproc: .asciiz "procedure example"
strnl: .ascii "\n"

.text
printnl: li $v0, 1
li $a0, 5
syscall

#jal printnl

li $v0, 1
li $a0, 1
syscall

However, I'd really like to be able to only execute the instructions associated with the printnl label when jumped and linked to (when 'called'). Is this feasible in MIPS? Feel free to criticize my design inclinations as part of your answer. I'm not sure how I should go about writing a simple assembly program who may have need of a lot of repeated instructions.

I did try this (but it doesn't assemble):

.data
strproc: .asciiz "procedure example"
strnl: .ascii "\n"

printnl: li $v0, 1
li $a0, 5
syscall

.text
li $v0, 1
li $a0, 1
syscall
jal printnl

Just put the routine at a point where control flow normally doesn't reach it, e.g. after your main routine. — fuz, Sep 30 '18 at 01:06
Could you give me an example? What are the semantics of 'main routine' in MIPS? It seems like there are some directives for this but I haven't dug up the right ones yet. — lonious, Sep 30 '18 at 01:08
Execution progresses from one instruction to the next unless you redirect it. In SPIM I guess execution begins at the beginning of the text segment. You exit your program by executing system call 10. If you put your routine after that, control never reaches it unless you call it explicitly. — fuz, Sep 30 '18 at 01:14

score 1 · Accepted Answer · answered Sep 30 '18 at 01:18

Execution progresses from one instruction to the next unless you redirect it. In SPIM I guess execution begins at the beginning of the text segment and ends when you invoke an exit system call (system call #10). If you put your routine after an exit system call, a function return, or any other unconditional branch, control never reaches it unless you call it explicitly. For example:

        .data
strproc:.asciiz "procedure example"
strnl:  .ascii "\n"

        .text
        # entry point
        li $v0, 1
        li $a0, 1
        syscall     # print integer 1

        jal println # call println

        li $v0, 10
        syscall     # exit program

printnl:li $v0, 1
        li $a0, 5
        syscall     # print integer 5
        jr $ra      # return from function

MIPS-Assembly: How to 'define' subroutine for later use

1 Answers1