CODEWITHSUNDEEP
cassemblymips
Daniel Oliveira
Daniel Oliveira

Reputation: 1290

MIPS - Call C function in Assembly code

I am trying to call a function declared in a C file from an assembly file, but I am getting a "Illegal Instruction" error.

My C code:

#include <stdio.h>

int BubbleSort(int *v){
    return 13;
}

int Run(int *, int *);


int main(){
    int vetor[] = {1, 3, 5, 4, 10}, numTrocas = 0, res = 0;
    numTrocas = Run(vetor, &res);   
    printf("numTrocas= %d\nf= %d\n", numTrocas, res);
    return 0;
}

My Assembly code:

.data 
.text 
.globl Run

Run:
    addi $sp,$sp,-8
    sw $ra,0($sp)
    sw $a0,4($sp)
    move $t4, $a1 #$t4 = $a1; address of variable res in C file
    move $t6, $a0 #$t6 = address of the first vector element

    lw $a0, ($t6)
    add $t6, $t6, 4
    lw $a1, ($t6)
    add $t6, $t6, 4
    lw $a2, ($t6)
    add $t6, $t6, 4
    lw $a3, ($t6)
    add $t6, $t6, 4
    lw $t3, ($t6)
    jal PolyCalc

    lw $a0,4($sp)
    jal BubbleSort #-> Illegal Instruction

    lw $ra, 0($sp)
    addi $sp, $sp, 8 
    jr $ra

PolyCalc: #This function calculates the result of the expression 5(V[0] + V[1])(V[2] − 3xV[3]xV[4])
    li $s0,5             #$s0 = 5
    li $s1,3             #$s1 = 3
    add $t1,$a0,$a1      #t1=(x1+x2)
    mul $t1,$t1,$s0      #t1=5*(x1+x2)
    mul $t2,$a3,$t3      #$t2 = x4*x5
    mul $t2,$t2,$s1      #$t2 = 3*x4*x5
    sub $t2,$a2,$t2      #$t2 = (x3-3x4*x5)
    mul $t1,$t1,$t2      
    sw $t1, ($t4) #Save the result on the address of $t4
    jr $ra

When I comment the line jal BubbleSort and add a random value to $v0 as a return of the BubbleSort function I stop getting that error and the program works fine.

Can someone find the error in my code? Thanks

Upvotes: 4

Views: 2141

Answers (2)

Craig Estey
Craig Estey

Reputation: 33601

For good measure, in your asm file, you should probably add:

.extern BubbleSort

Then, the jal BubbleSort should get relocated correctly.

But, the linker may place it too far away for the [limited] range of jal, so you may have to replace it with:

la $t0,BubbleSort
jalr $t0

Upvotes: 2

Oscar Forner Martinez
Oscar Forner Martinez

Reputation: 1

The error you are experiencing is because the assembly code is not able to find the label called BubbleSort to jump. I think you should be using a different approach. You can embed assembly code in C using the asm function.

Something like:

#include <stdio.h>

int BubbleSort(int *v){
    asm("lw $a0, ($t6)"
    "lw $a1, ($t6)");
}

int Run(int *, int *);


int main(){
    int vetor[] = {1, 3, 5, 4, 10}, numTrocas = 0, res = 0;
    numTrocas = Run(vetor, &res);   
    printf("numTrocas= %d\nf= %d\n", numTrocas, res);
    return 0;
}

You can find more information about this function in the GCC documentation: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html

Upvotes: -1

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