I’ve been tasked with implementing a few image processing functions in RISC-V assembly, using .GRAY images, and wrote a prototype in C to have some sort of guideline, which reads like so

#include <stdio.h>

#define width 400
#define height 599

//read image's pixels
void readGray(unsigned char image[width][height]) {
    FILE *source = fopen("cat_noisy.gray", "rb");

    fread(image, sizeof(unsigned char), width * height, source); /*read through the file*/
    fclose(source);
}
void writeGray(unsigned char image[width][height]) {
    FILE *file = fopen("cat_mean.gray", "wb");

    fwrite(image, sizeof(unsigned char), width * height, file);
    fclose(file);
}

When trying to accomplish the same in RISC-V assembly, I’ve got this read function

.data
input: .asciz "cat_noisy.gray"
output_mean: .asciz "cat_mean.gray"
output_median: .asciz "cat_median.gray"
error: .asciz "erro a ler ficheiro"
status_read: .asciz "image read"
status_write: .asciz "image written"
image: .space 239600 # (599 * 400)
.text
.global main

readGray: 
    #args
    addi sp, sp, -8 # make space in stack
    sb s0, 0(sp) # store image name byte in stack
    sb s1, 4(sp) # store image size byte in stack
    
    #opening file
    mv s0, a1 # move to where array will be saved
    li a7, 1024 # syscall to open file
    li a1, 0 # syscall to read file
    ecall #open file
    mv s1, a0 # save descriptive in s1
    
    beqz a0, readGray_error # if failed, show error
    
    #if success, read
    li a7, 63 # syscall to read file
    mv a0, s1 # save descriptive in a0
    mv a1, s0 # save image array in a1
    li a2, 239600 # read up to 239600 bytes - image size
    ecall # read file
    
readGray_done: #close file and reset args
    li a7, 57 
    mv a0, s1 
    ecall 
    li a0, 0 
    li a1, 0 
    li a2, 0 
    
    addi sp, sp, 8 
    lb a0, 0(sp)
    lb a1, 4(sp) 
    
#print success
    la a0, status_read 
    li a7, 4 
    ecall 
    ret 
    
readGray_error: #print error 
    la a0, error
    li a7, 4
    ecall 
    j readGray_done

And this write function

writeGray: 
    #args
    addi sp, sp, -8 
    sw s0, 0(sp) 
    sw s1, 4(sp) 
    
    mv s0, a1 
    li a7, 1024 
    li a1, 1 
    ecall 
    mv s1, a0 
    
    beqz a0, writeGray_error 
    
    li a7, 64
    mv a0, s1 
    mv a1, s0
    li a2, 239600
    ecall

    
writeGray_done:
    li a7, 57 
    mv a0, s0
    ecall
    
    li a0, 0 
    li a1, 0 
    li a2, 0 
    
    addi sp, sp, 8 
    lb a0, 0(sp) 
    lb a1, 4(sp) 
    
    la a0, status_write 
    li a7, 4
    ecall 
    ret 
    
writeGray_error: 
    la a0, error 
    li a7, 4 
    ecall 
    j writeGray_done 

And here’s my main function

# readGray
    la a0, input
    la a1, image
    jal readGray 
    
    # writeGray
    la a0, input
    la a1, image 
    jal writeGray
    
    #exit
    li a7, 10 
    ecall 

``

The issue I've run across is the image either fails to generate, or just generates a black .PNG image (after converting with ImageMagick), even when using my input image - defined in the .data segment - for both read and write (that should make a copy).

Thank you for all the help in advance, apologies for the long post.