compooter-enhensa/1-reg-reg-decode/main.c

#include "../common.h"

static void
decode_and_print_reg_reg_movs(u8 *data, u64 size)
{
    printf("bits 16\n\n");
    
    /* We do not handle corrupt binaries */
    
    for (u64 i = 0; i < size; i += 2) {
        u8 b1 = data[i + 0];
        u8 b2 = data[i + 1];
        
        u8 D_flag = (b1 & 0x2) >> 1;
        u8 W_flag = b1 & 0x1;
        
        u8 mod       = (b2 & 0xC0) >> 6;
        u8 reg_field = (b2 & 0x38) >> 3;
        u8 rm_field  = b2 & 0x7;
        
        const char **regs = W_flag ? REGS_W1 : REGS_W0;
        const char **rms = W_flag ? RM_W1 : RM_W0;
        
        if (D_flag) {
            /* Instruction destination is specified in REG field */
            printf("mov %s, %s\n", regs[reg_field], rms[rm_field]);
        } else {
            /* Instruction source is specified in REG field */
            printf("mov %s, %s\n", rms[rm_field], regs[reg_field]);
        }
    }
}

int
main(int argc, char **argv)
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s binary_file\n", argv[0]);
        return(1);
    }
    
    char *filename = argv[1];
    int fd = open(filename, O_RDONLY);
    
    if (fd == -1) {
        perror("open");
        return(1);
    }
    
    u64 size = file_size(fd);
    u8 *data = read_file(fd, size);
    
    decode_and_print_reg_reg_movs(data, size);
    
    return(0);
}