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complete challenge homework 2

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This commit is contained in:
Rokas Puzonas 2023-04-09 21:19:30 +03:00
parent 8e4f7419a1
commit 5b67cb4e25
1 changed files with 87 additions and 20 deletions
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107
src/asm.c
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@ -6,6 +6,8 @@
#define u32 uint32_t
#define u16 uint16_t
#define u8 uint8_t
#define i16 int16_t
#define i8 int8_t
#define todo(...) fprintf(stderr, "TODO(%s:%d): ", __FILE__, __LINE__); fprintf(stderr, __VA_ARGS__); abort()
#define dbg(...) printf("; "); printf(__VA_ARGS__); printf("\n")
@ -13,7 +15,8 @@
const char *wide_reg_names[8] = { "ax", "cx", "dx", "bx", "sp", "bp", "si", "di" };
const char *non_wide_reg_names[8] = { "al", "cl", "dl", "bl", "ah", "ch", "dh", "bh" };
const char *mod_lookup_names[8] = {
// eac - Effective address calculation
const char *eac_names[8] = {
"bx + si",
"bx + di",
"bp + si",
@ -33,6 +36,37 @@ const char *lookup_reg_name(u8 idx, bool wide) {
}
}
void snprintf_mod_with_disp(char *rm_name, size_t size, u8 rm, i16 displacement) {
if (displacement < 0) {
snprintf(rm_name, size, "[%s - %d]", eac_names[rm], -displacement);
} else {
snprintf(rm_name, size, "[%s + %d]", eac_names[rm], displacement);
}
}
void get_rm_name(char *rm_name, size_t size, FILE *src, u8 rm, u8 mod, bool wide) {
if (mod == 0b11000000) { // Mod = 0b11
strcpy(rm_name, lookup_reg_name(rm, wide));
} else if (mod == 0b10000000) { // Mod = 0b10
i16 displacement = fgetc(src) | (fgetc(src) << 8);
snprintf_mod_with_disp(rm_name, size, rm, displacement);
} else if (mod == 0b01000000) { // Mod = 0b01
i16 displacement = fgetc(src);
if (displacement & 0b10000000) {
displacement |= (0b11111111 << 8);
}
snprintf_mod_with_disp(rm_name, size, rm, displacement);
} else if (mod == 0b00000000) { // Mod = 0b00
if (rm == 0b110) { // Direct address
u16 displacement = fgetc(src) | (fgetc(src) << 8);
snprintf(rm_name, size, "[%d]", displacement);
} else {
snprintf(rm_name, size, "[%s]", eac_names[rm]);
}
}
}
// Handy reference: Table 4-12. 8086 Instruction Encoding
void dissassemble(FILE *src, FILE *dst) {
fprintf(dst, "bits 16\n\n");
while (true) {
@ -50,40 +84,73 @@ void dissassemble(FILE *src, FILE *dst) {
u8 rm = byte2 & 0b00000111;
const char *reg_name = lookup_reg_name(reg, wide);
char rm_name[24] = { 0 };
if (mod == 0b11000000) { // Mod = 0b11
strcpy(rm_name, lookup_reg_name(rm, wide));
} else if (mod == 0b10000000) { // Mod = 0b10
u16 immidiate = fgetc(src) | (fgetc(src) << 8);
snprintf(rm_name, sizeof(rm_name), "[%s + %d]", mod_lookup_names[rm], immidiate);
} else if (mod == 0b01000000) { // Mod = 0b01
u8 immidiate = fgetc(src);
snprintf(rm_name, sizeof(rm_name), "[%s + %d]", mod_lookup_names[rm], immidiate);
} else if (mod == 0b00000000) { // Mod = 0b00
if (rm == 0b110) { // Direct address
todo("direct address");
} else {
snprintf(rm_name, sizeof(rm_name), "[%s]", mod_lookup_names[rm]);
}
}
get_rm_name(rm_name, sizeof(rm_name), src, rm, mod, wide);
if (direction) {
fprintf(dst, "mov %s, %s\n", reg_name, rm_name);
} else {
fprintf(dst, "mov %s, %s\n", rm_name, reg_name);
}
// Immediate to register
} else if ((byte1 & 0b11110000) == 0b10110000) {
bool wide = (byte1 & 0b1000) >> 3;
u8 reg = byte1 & 0b111;
u16 immidiate;
u16 immediate;
if (wide) {
immidiate = fgetc(src) | (fgetc(src) << 8);
immediate = fgetc(src) | (fgetc(src) << 8);
} else {
immidiate = fgetc(src);
immediate = fgetc(src);
}
fprintf(dst, "mov %s, %d\n", lookup_reg_name(reg, wide), immidiate);
fprintf(dst, "mov %s, %d\n", lookup_reg_name(reg, wide), immediate);
// Immediate to memory
} else if ((byte1 & 0b11111110) == 0b11000110) {
u8 byte2 = fgetc(src);
bool wide = byte1 & 0b1;
u8 mod = byte2 & 0b11000000;
u8 rm = byte2 & 0b00000111;
char rm_name[24] = { 0 };
get_rm_name(rm_name, sizeof(rm_name), src, rm, mod, wide);
u16 immediate;
if (wide) {
immediate = fgetc(src) | (fgetc(src) << 8);
fprintf(dst, "mov %s, word %d\n", rm_name, immediate);
} else {
immediate = fgetc(src);
fprintf(dst, "mov %s, byte %d\n", rm_name, immediate);
}
// Memory to accumulator
} else if ((byte1 & 0b11111110) == 0b10100000) {
bool wide = byte1 & 0b1;
u16 immediate;
if (wide) {
immediate = fgetc(src) | (fgetc(src) << 8);
} else {
immediate = fgetc(src);
}
fprintf(dst, "mov ax, [%d]\n", immediate);
// Accumulator to memory
} else if ((byte1 & 0b11111110) == 0b10100010) {
bool wide = byte1 & 0b1;
u16 immediate;
if (wide) {
immediate = fgetc(src) | (fgetc(src) << 8);
} else {
immediate = fgetc(src);
}
fprintf(dst, "mov [%d], ax\n", immediate);
} else {
todo("unhandled byte %d", byte1);
}