WIP Refactor: Instruction parser now works and basic decoding in place
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4754a8cd4c
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8497316768
131
decode.c
131
decode.c
@ -3,8 +3,6 @@
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#include "lib.h"
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#include <sys/stat.h>
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#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
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enum InstructionType
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{
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INST_MOV_REG_REG = 0b10001000,
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@ -92,9 +90,19 @@ static i16 get_data(unsigned char* buf, char wide)
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// Cast buf[0] to sbyte if not the conversion to i16 won't detect signedness
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return wide == 1 ? (i16)buf[1] << 8 | buf[0] : (sbyte)buf[0];
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}
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#define IS_INST(value, m, inst) ((value & ~m) == (char)inst)
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typedef struct InstMask {char *name; u8 mask; u8 code;} InstMask;
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static u8 mask_and_shift(u8 value, u8 mask)
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{
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value &= mask;
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int count = 0;
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while ((mask & 0x1) == 0 && count < 8)
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{
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value >>= 1;
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mask >>= 1;
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count++;
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}
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return value;
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}
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typedef struct InstFormat
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{
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@ -103,7 +111,7 @@ typedef struct InstFormat
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u8 inst_enc;
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u8 mask_inst;
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u8 mask_w;
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u64 mask_reg;
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u8 mask_reg;
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bool has_operands;
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bool has_displacement;
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bool has_data;
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@ -122,14 +130,15 @@ InstFormat inst_formats[] =
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// MOV
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////////
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// Register/memory to/from register
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{.id=1, .name="mov", .inst_enc=0b10001000, .mask_inst=0x3, .has_operands=true, .has_displacement=true,
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.has_d=true, .has_w=true, .has_reg=true, .has_mod=true, .has_rm=true},
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{.id=1, .name="mov", .inst_enc=0b10001000, .mask_inst=0x3, .mask_reg=0b00111000,
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.mask_w=0x1, .has_operands=true, .has_displacement=true, .has_d=true, .has_w=true,
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.has_reg=true, .has_mod=true, .has_rm=true},
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// Immediate to register/memory
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{.id=2, .name="mov", .inst_enc=0b11000110, .mask_inst=0x1, .mask_w=0x1, .has_operands=true,
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.has_displacement=true, .has_data=true, .has_w=true, .has_mod=true, .has_rm=true},
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// Immediate to register
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{.id=3, .name="mov", .inst_enc=0b10110000, .mask_inst=0xF, .mask_w=0x8,
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.mask_reg=0x0b00000111, .has_data=true, .has_w=true},
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.mask_reg=0b00000111, .has_data=true, .has_w=true},
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// Memory to accumulator | Accumulator to memory using the `d` bit
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// even though the manual doesn't specify it
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{.id=4, .name="mov", .inst_enc=0b10100000, .mask_inst=0x3, .mask_w=0x1,
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@ -153,35 +162,97 @@ InstFormat inst_formats[] =
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Instruction parse_instruction(u8* buf)
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{
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u8 inst = buf[0];
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InstFormat format;
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InstFormat fmt;
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bool matched_inst = false;
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// TODO: This might be a good time to learn how to make a hashtable in C
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for (u16 i = 0; i < sizeof(inst_formats) / sizeof(InstFormat); i++)
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{
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if ((inst & ~inst_formats[i].mask_inst) == inst_formats[i].inst_enc)
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{
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format = inst_formats[i];
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fmt = inst_formats[i];
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matched_inst = true;
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break;
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}
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}
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if (!matched_inst)
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return (Instruction){.bytes_read = 0};
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u8_opt d_opt = none_u8();
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u8_opt s_opt = none_u8();
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u8_opt w_opt = none_u8();
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u8_opt reg_opt = none_u8();
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u8_opt mod_opt = none_u8();
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u8_opt rm_opt = none_u8();
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u16_opt data_opt = none_u16();
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u16_opt displacement_opt = none_u16();
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if (fmt.has_d) d_opt = some_u8((inst & 0x2) >> 1);
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if (fmt.has_s) s_opt = some_u8((inst & 0x2) >> 1);
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if (fmt.has_rm) rm_opt = some_u8(buf[1] & 0x7);
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if (fmt.has_mod) mod_opt = some_u8((buf[1] & 0b11000000) >> 6);
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if (fmt.has_w) w_opt = some_u8(mask_and_shift(buf[0], fmt.mask_w));
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if (fmt.has_reg)
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{
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u8 reg = fmt.has_operands ? buf[1] : buf[0];
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reg_opt = some_u8(mask_and_shift(reg, fmt.mask_reg));
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}
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if (fmt.has_data)
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{
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u8 idx = 1;
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if (fmt.has_operands) idx += 1;
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if (fmt.has_displacement) idx += mod_opt.value % 3;
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u16 data = w_opt.value != 0 ? (i16)buf[idx+1] << 8 | buf[0] : (sbyte)buf[idx];
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data_opt = some_u16(data);
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}
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if (fmt.has_displacement && mod_opt.value % 3 > 0)
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{
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u16 disp = mod_opt.value == MODE_MEM_DIS_16
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? (i16)buf[3] << 8 | buf[2]
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: (sbyte)buf[3];
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displacement_opt = some_u16(disp);
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}
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u16 bytes_read = 1;
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bytes_read += fmt.has_operands ? 1 : 0;
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// This is a trick because mod == 1 and mod == 2 will displace one and two bytes
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// respectively but mod == 3 wraps to 0 since it doesn't displace
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if (fmt.has_displacement) bytes_read += mod_opt.value % 3;
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if (fmt.has_data) bytes_read += w_opt.value == 0 ? 1 : 2;
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return (Instruction) {
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.id = format.id,
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.name = format.name,
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.data = none_u16(),
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.displacement = none_u16(),
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.w = none_u8(),
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.d = none_u8(),
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.s = none_u8(),
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.mod = none_u8(),
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.reg = none_u8(),
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.rm = none_u8(),
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.bytes_read = 2,
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.id = fmt.id,
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.name = fmt.name,
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.data = data_opt,
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.displacement = displacement_opt,
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.w = w_opt,
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.d = d_opt,
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.s = s_opt,
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.mod = mod_opt,
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.reg = reg_opt,
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.rm = rm_opt,
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.bytes_read = bytes_read,
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};
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}
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void decode_instruction(char* str_buf, Instruction inst)
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{
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IF_LET_SOME(u8, mod, inst.mod)
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{
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if (mod == MODE_RGSTR_MODE)
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{
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Register reg = registers[(size_t)inst.reg.value];
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Register rm = registers[(size_t)inst.rm.value];
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Register src_reg = inst.d.value == 0 ? reg : rm;
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Register dst_reg = inst.d.value == 0 ? rm : reg;
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char *src_name = reg_name(src_reg, inst.w.value);
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char *dst_name = reg_name(dst_reg, inst.w.value);
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sprintf(str_buf, "%s %s, %s ;%d", inst.name, dst_name, src_name, inst.id);
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}
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}
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else
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{
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sprintf(str_buf, "%s ;%d", inst.name, inst.id);
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}
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}
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bool mov_inst(FILE* f, unsigned char* buf, char inst)
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{
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size_t bytes_read;
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@ -205,8 +276,6 @@ bool mov_inst(FILE* f, unsigned char* buf, char inst)
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else
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{
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bool is_direct_addr = mod == 0 && rm == 0b110;
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// This is a trick because mod == 1 and mod == 2 will displace one and two bytes
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// respectively but mod == 3 wraps to 0 since it doesn't displace
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int bytes_to_read = is_direct_addr ? 2 : mod % 3;
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bytes_read = fread(buf, sizeof(char), bytes_to_read, f);
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char* eac_name = is_direct_addr ? "" : get_eac_registers(rm);
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@ -381,21 +450,29 @@ int main(int argc, char** argv)
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printf("; Decoded 8086 Assembly Instructions\n\n");
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printf("bits 16\n\n");
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char *inst_str_buf = malloc(sizeof(char) * 256);
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u32 bytes_processed = 0;
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while (bytes_processed < bytes_read)
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{
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Instruction inst = parse_instruction(buffer+bytes_processed);
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bytes_processed += inst.bytes_read;
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Instruction inst = parse_instruction(buffer + bytes_processed);
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// char inst = buffer[0];
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// if (mov_inst(f, buffer, inst)) goto handled;
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// if (add_inst(f, buffer, inst)) goto handled;
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if (inst.name != NULL)
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printf("%s ;%d", inst.name, inst.id);
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if (inst.bytes_read > 0)
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{
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decode_instruction(inst_str_buf, inst);
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printf("%s", inst_str_buf);
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bytes_processed += inst.bytes_read;
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}
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else
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{
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bytes_processed += 1;
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fprintf(stderr, "___Unrecognized Instruction___");
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}
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// handled:
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printf("\n");
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}
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free(inst_str_buf);
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free(buffer);
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}
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6
lib.h
6
lib.h
@ -23,7 +23,7 @@ enum OptionTag {NONE, SOME};
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enum OptionTag tag; \
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union { \
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char none; \
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type some; \
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type value; \
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}; \
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} type##_opt; \
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\
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@ -34,13 +34,13 @@ enum OptionTag {NONE, SOME};
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\
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static inline type##_opt some_##type(type value) \
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{ \
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return (type##_opt){ .tag = SOME, .some = value }; \
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return (type##_opt){ .tag = SOME, .value = value }; \
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} \
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\
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static inline int get_some_##type(type##_opt opt, type* out_value) \
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{ \
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if (opt.tag != SOME) return 0; \
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*out_value = opt.some; \
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*out_value = opt.value; \
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return 1; \
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}
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