MIPS - Call C function in Assembly code - c

Question

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

Answer 1

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

Answer 2

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