MIPS “la” pseudo instruction loads a literal's address

Question

I have two questions here :

1)> What is happening in line 2.The 'la' pseudo instruction refers to load address, instead of the literal '3444' there should have been a label.How can it load the address of the literal

2)> if you replace line 3 with "li $a0 3444" which loads 3444 into the register #a0 instead of the address.The output is still the same.What i want to ask from this is that how could syscall know that in #a0 is the address of the variable or the variable itself.How could the subroutine for printing the integer work correctly whether the argument stored in #a0 is the address or the integer value itself.

.text

      li $v0 1 
 >>2  la $a0 3444   # When i replace 3444 literal with the label  'anint' it makes sense and the output of course is the same
      syscall


.data

 anint: .word 3444

Output:

UPDATE#2: I could'nt post the code in a comment so...

IF la(load address) and li(load immediate) both translate to the same instruction i-e loading the literal into #a0 then explain Line 3 from the code segment below.

      .text


      li #v0 4
>>3   la #a0 msg  #This loads the address of the label 'msg in #a0' not the label itself    
      syscall





      .data

       msg: .asciiz "This is a long string that can't be saved in the register!"

You shouldn't try to post code in comments anyway. Editing clarifications into your answer is the correct thing to do. — Peter Cordes
labels are addresses. They aren't "stored" anywhere themselves, they're just useful ways to write addresses symbolically instead of with numeric addresses. — Peter Cordes

Michael Michael · Accepted Answer · 2016-09-25T16:41:58

how could syscall know that in #a0 is the address of the variable or the variable itself

It doesn't. System call 1 in SPIM/MARS always prints the value in $a0.

li $a0,3444 and la $a0,3444 are translated into the same thing (some instruction that loads the value 3334 into register $a0, such as ori $a0, $0, 3334).

MIPS “la” pseudo instruction loads a literal's address

1 Answers