120 lines
2.5 KiB
C++
120 lines
2.5 KiB
C++
#include <bits/types/FILE.h>
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#include <cstdint>
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#include <stdint.h>
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#include <stdio.h>
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#include <string.h>
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// Bit patterns for the 8086 OPCODES
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enum class OPCODES {
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MOV = 0x88,
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};
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enum class OPMASKS {
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MOV = 0xfc,
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};
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enum class FLAGS {
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WORD = 0x01,
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REG_DEST = 0x02,
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};
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enum class MODE {
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MEM = 0x00,
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MEM8 = 0x40,
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MEM16 = 0x80,
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REG = 0xc0,
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};
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uint16_t decode_mode(uint16_t instruction);
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void decode_register(uint16_t instruction, bool word, char *dest);
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int main(int argc, char *argv[]) {
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if (argc < 2) {
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printf("Please provide a file to disassemble\n");
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return 1;
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}
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const char *filename = argv[1];
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FILE *fp = fopen(filename, "rb");
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if (fp) {
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uint16_t inst = 0;
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const char *op = "";
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char out_filename[4096] = {0};
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sprintf(out_filename, "%s_out.asm", filename);
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FILE *out = fopen(out_filename, "w");
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if (out) {
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fprintf(out, "; Disassembled by DASM\n\nbits 16\n\n");
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while (fread(&inst, sizeof(inst), 1, fp)) {
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if ((inst & (uint16_t)OPMASKS::MOV) == (uint16_t)OPCODES::MOV) {
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op = "mov";
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bool reg_dest =
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(inst & (uint16_t)FLAGS::REG_DEST) == (uint16_t)FLAGS::REG_DEST;
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bool word = (inst & (uint16_t)FLAGS::WORD) == (uint16_t)FLAGS::WORD;
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uint16_t operands_info = inst >> 8;
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if (decode_mode(operands_info) == (uint16_t)MODE::REG) {
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char rm[3] = {0};
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char reg[3] = {0};
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decode_register(operands_info, word, rm);
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decode_register(operands_info >> 3, word, reg);
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fprintf(out, "%s %s, %s\n", op, reg_dest ? reg : rm,
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reg_dest ? rm : reg);
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}
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} else {
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printf("It's not a mov operation\n");
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}
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}
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fclose(out);
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} else {
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printf("Failed to open output file\n");
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}
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fclose(fp);
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} else {
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printf("Failed to open the selected file\n");
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}
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return 0;
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}
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uint16_t decode_mode(uint16_t instruction) {
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uint16_t mode_mask = 0xc0;
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return instruction & mode_mask;
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}
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void decode_register(uint16_t instruction, bool word, char *dest) {
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static uint16_t reg_mask = 0x07;
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// clang-format off
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static const char *table[16] = {
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"al", "ax",
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"cl", "cx",
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"dl", "dx",
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"bl", "bx",
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"ah", "sp",
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"ch", "bp",
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"dh", "si",
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"bh", "di"
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};
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// clang-format on
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static const uint16_t ROW_WIDTH = 2;
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uint16_t offset = instruction & reg_mask;
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// Multiply offset by 2 since each row has 2 columns
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strcpy(dest, table[offset * ROW_WIDTH + (uint16_t)word]);
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}
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