WIP Refactor: Instruction parser now works and basic decoding in place

decode.c

@@ -1,10 +1,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include "lib.h"
+#include <sys/stat.h>
 
-#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
-
-enum Instruction
+enum InstructionType
 {
     INST_MOV_REG_REG = 0b10001000,
     // INST_MOV_REG_REG = 0b10001000,
@@ -24,15 +23,11 @@ typedef struct Register
     char code;
     char* fullname;
     char* bytename;
-
-    union
-    {
-        struct
-        {
+    union {
+        struct {
             char low;
             char high;
         };
-
         u16 full;
     } value;
 } Register;
@@ -48,9 +43,23 @@ Register registers[8] = {
     {.code = 0b111, .fullname = "di", .bytename = "bh"},
 };
 
-char* memory[65536];
+typedef struct Instruction
+{
+    u16 id;
+    char *name;
+    u16_opt data;
+    u16_opt displacement;
+    u8_opt w;
+    u8_opt d;
+    u8_opt s;
+    u8_opt mod;
+    u8_opt reg;
+    u8_opt rm;
+    u8_opt SR;
+    u8 bytes_read;
+} Instruction;
 
-// void inst_mov_rgmm_reg()
+char *memory[65536];
 
 /// Get Effective Address Calculation Registers
 char* get_eac_registers(char rm)
@@ -58,48 +67,192 @@ char* get_eac_registers(char rm)
     char* reg_name;
     switch (rm)
     {
-    case 0b000:
-        reg_name = "bx + si";
-        break;
-    case 0b001:
-        reg_name = "bx + di";
-        break;
-    case 0b010:
-        reg_name = "bp + si";
-        break;
-    case 0b011:
-        reg_name = "bp + di";
-        break;
-    case 0b100:
-        reg_name = "si";
-        break;
-    case 0b101:
-        reg_name = "di";
-        break;
-    case 0b110:
-        reg_name = "bp";
-        break;
-    case 0b111:
-        reg_name = "bx";
-        break;
-    default:
-        perror("Invalid R/M value");
-        exit(1);
+    case 0b000: reg_name = "bx + si"; break;
+    case 0b001: reg_name = "bx + di"; break;
+    case 0b010: reg_name = "bp + si"; break;
+    case 0b011: reg_name = "bp + di"; break;
+    case 0b100: reg_name = "si";      break;
+    case 0b101: reg_name = "di";      break;
+    case 0b110: reg_name = "bp";      break;
+    case 0b111: reg_name = "bx";      break;
+    default: perror("Invalid R/M value"); exit(1);
     }
     return reg_name;
 }
 
-static inline char* reg_name(Register reg, char wide)
+static char* reg_name(Register reg, char wide)
 {
     return wide == 1 ? reg.fullname : reg.bytename;
 }
 
-static inline i16 get_data(unsigned char* buf, char wide)
+static i16 get_data(unsigned char* buf, char wide)
 {
     // Cast buf[0] to sbyte if not the conversion to i16 won't detect signedness
     return wide == 1 ? (i16)buf[1] << 8 | buf[0] : (sbyte)buf[0];
 }
 
+static u8 mask_and_shift(u8 value, u8 mask)
+{
+    value &= mask;
+    int count = 0;
+    while ((mask & 0x1) == 0 && count < 8)
+    {
+        value >>= 1;
+        mask >>= 1;
+        count++;
+    }
+    return value;
+}
+
+typedef struct InstFormat
+{
+    u16 id;
+    char *name;
+    u8 inst_enc;
+    u8 mask_inst;
+    u8 mask_w;
+    u8 mask_reg;
+    bool has_operands;
+    bool has_displacement;
+    bool has_data;
+    bool has_d;
+    bool has_w;
+    bool has_reg;
+    bool has_mod;
+    bool has_rm;
+    bool has_s;
+    bool has_SR;
+} InstFormat;
+
+InstFormat inst_formats[] =
+{
+    ////////
+    // MOV
+    ////////
+    // Register/memory to/from register
+    {.id=1, .name="mov", .inst_enc=0b10001000, .mask_inst=0x3, .mask_reg=0b00111000,
+     .mask_w=0x1, .has_operands=true, .has_displacement=true, .has_d=true, .has_w=true,
+     .has_reg=true, .has_mod=true, .has_rm=true},
+    // Immediate to register/memory
+    {.id=2, .name="mov", .inst_enc=0b11000110, .mask_inst=0x1, .mask_w=0x1, .has_operands=true,
+     .has_displacement=true, .has_data=true, .has_w=true, .has_mod=true, .has_rm=true},
+    // Immediate to register
+    {.id=3, .name="mov", .inst_enc=0b10110000, .mask_inst=0xF, .mask_w=0x8,
+     .mask_reg=0b00000111, .has_data=true, .has_w=true},
+    // Memory to accumulator | Accumulator to memory using the `d` bit
+    // even though the manual doesn't specify it
+    {.id=4, .name="mov", .inst_enc=0b10100000, .mask_inst=0x3, .mask_w=0x1,
+     .has_data=true, .has_w=true, .has_d=true},
+    // Register/memory to segment register and inverse using the `d` bit
+    {.id=5, .name="mov", .inst_enc=0b10001100, .mask_inst=0x3, .has_SR=true, .has_d=true,
+     .has_displacement=true, .has_mod=true, .has_rm=true},
+    ////////
+    // ADD
+    ////////
+    // Reg/memory with register or either
+    {.id=6, .name="add", .inst_enc=0b00000000, .mask_inst=0x3, .mask_w=0x1,
+     .has_operands=true, .has_displacement=true, .has_w=true,
+     .has_d=true, .has_reg=true, .has_mod=true, .has_rm=true},
+    // Immediate to register/memory
+    {.id=7, .name="add", .inst_enc=0b10000000, .mask_inst=0x3, .mask_w=0x1, .has_w=true,
+     .has_operands=true, .has_displacement=true, .has_data=true, .has_mod=true, .has_rm=true},
+    {.id=8, .name="add", .inst_enc=0b00000100, .mask_inst=0x1, .mask_w=0x1, .has_data=true, .has_w=true},
+};
+
+Instruction parse_instruction(u8* buf)
+{
+    u8 inst = buf[0];
+    InstFormat fmt;
+    bool matched_inst = false;
+    // TODO: This might be a good time to learn how to make a hashtable in C
+    for (u16 i = 0; i < sizeof(inst_formats) / sizeof(InstFormat); i++)
+    {
+        if ((inst & ~inst_formats[i].mask_inst) == inst_formats[i].inst_enc)
+        {
+            fmt = inst_formats[i];
+            matched_inst = true;
+            break;
+        }
+    }
+    if (!matched_inst)
+        return (Instruction){.bytes_read = 0};
+    u8_opt d_opt = none_u8();
+    u8_opt s_opt = none_u8();
+    u8_opt w_opt = none_u8();
+    u8_opt reg_opt = none_u8();
+    u8_opt mod_opt = none_u8();
+    u8_opt rm_opt = none_u8();
+    u16_opt data_opt = none_u16();
+    u16_opt displacement_opt = none_u16();
+
+    if (fmt.has_d) d_opt = some_u8((inst & 0x2) >> 1);
+    if (fmt.has_s) s_opt = some_u8((inst & 0x2) >> 1);
+    if (fmt.has_rm) rm_opt = some_u8(buf[1] & 0x7);
+    if (fmt.has_mod) mod_opt = some_u8((buf[1] & 0b11000000) >> 6);
+    if (fmt.has_w) w_opt = some_u8(mask_and_shift(buf[0], fmt.mask_w));
+    if (fmt.has_reg)
+    {
+        u8 reg = fmt.has_operands ? buf[1] : buf[0];
+        reg_opt = some_u8(mask_and_shift(reg, fmt.mask_reg));
+    }
+    if (fmt.has_data)
+    {
+        u8 idx = 1;
+        if (fmt.has_operands) idx += 1;
+        if (fmt.has_displacement) idx += mod_opt.value % 3;
+        u16 data = w_opt.value != 0 ? (i16)buf[idx+1] << 8 | buf[0] : (sbyte)buf[idx];
+        data_opt = some_u16(data);
+    }
+    if (fmt.has_displacement && mod_opt.value % 3 > 0)
+    {
+        u16 disp = mod_opt.value == MODE_MEM_DIS_16
+            ? (i16)buf[3] << 8 | buf[2]
+            : (sbyte)buf[3];
+        displacement_opt = some_u16(disp);
+    }
+
+    u16 bytes_read = 1;
+    bytes_read += fmt.has_operands ? 1 : 0;
+        // This is a trick because mod == 1 and mod == 2 will displace one and two bytes
+        // respectively but mod == 3 wraps to 0 since it doesn't displace
+    if (fmt.has_displacement) bytes_read += mod_opt.value % 3;
+    if (fmt.has_data) bytes_read += w_opt.value == 0 ? 1 : 2;
+    return (Instruction) {
+        .id = fmt.id,
+        .name = fmt.name,
+        .data = data_opt,
+        .displacement = displacement_opt,
+        .w = w_opt,
+        .d = d_opt,
+        .s = s_opt,
+        .mod = mod_opt,
+        .reg = reg_opt,
+        .rm = rm_opt,
+        .bytes_read = bytes_read,
+    };
+}
+
+void decode_instruction(char* str_buf, Instruction inst)
+{
+    IF_LET_SOME(u8, mod, inst.mod)
+    {
+        if (mod == MODE_RGSTR_MODE)
+        {
+            Register reg = registers[(size_t)inst.reg.value];
+            Register rm = registers[(size_t)inst.rm.value];
+            Register src_reg = inst.d.value == 0 ? reg : rm;
+            Register dst_reg = inst.d.value == 0 ? rm : reg;
+            char *src_name = reg_name(src_reg, inst.w.value);
+            char *dst_name = reg_name(dst_reg, inst.w.value);
+            sprintf(str_buf, "%s %s, %s ;%d", inst.name, dst_name, src_name, inst.id);
+        }
+    }
+    else
+    {
+        sprintf(str_buf, "%s ;%d", inst.name, inst.id);
+    }
+}
+
 bool mov_inst(FILE* f, unsigned char* buf, char inst)
 {
     size_t bytes_read;
@@ -123,8 +276,6 @@ bool mov_inst(FILE* f, unsigned char* buf, char inst)
         else
         {
             bool is_direct_addr = mod == 0 && rm == 0b110;
-            // This is a trick because mod == 1 and mod == 2 will displace one and two bytes
-            // respectively but mod == 3 wraps to 0 since it doesn't displace
             int bytes_to_read = is_direct_addr ? 2 : mod % 3;
             bytes_read = fread(buf, sizeof(char), bytes_to_read, f);
             char* eac_name = is_direct_addr ? "" : get_eac_registers(rm);
@@ -262,27 +413,66 @@ int main(int argc, char** argv)
         printf("Usage: Please provide assembled instructions as input\n");
         exit(0);
     }
-    unsigned char buf[256];
+
+    struct stat st;
+    if (stat(argv[1], &st) == -1)
+    {
+        perror("Unable to get file size\n");
+        return EXIT_FAILURE;
+    }
+
+    unsigned char* buffer = malloc(st.st_size);
+    if (!buffer)
+    {
+        perror("Unable to allocate memory for binary file");
+        return EXIT_FAILURE;
+    }
+
     FILE *f = fopen(argv[1], "r");
     if (!f)
     {
         perror("fopen\n");
+        free(buffer);
         return EXIT_FAILURE;
     }
 
-    size_t bytes_read;
+    size_t bytes_read = fread(buffer, sizeof(unsigned char), st.st_size, f);
+    if (bytes_read != (size_t)st.st_size)
+    {
+        fprintf(stderr, "Read of binary file to memory incomplete.\n");
+        free(buffer);
+        fclose(f);
+        return EXIT_FAILURE;
+    }
+
+    fclose(f);
 
     printf("; Decoded 8086 Assembly Instructions\n\n");
     printf("bits 16\n\n");
 
-    while ((bytes_read = fread(buf, sizeof(char), 1, f)) > 0)
+    char *inst_str_buf = malloc(sizeof(char) * 256);
+    u32 bytes_processed = 0;
+    while (bytes_processed < bytes_read)
     {
-        char inst = buf[0];
-        if (mov_inst(f, buf, inst)) goto handled;
-        if (add_inst(f, buf, inst)) goto handled;
+        Instruction inst = parse_instruction(buffer + bytes_processed);
+        // char inst = buffer[0];
+        // if (mov_inst(f, buffer, inst)) goto handled;
+        // if (add_inst(f, buffer, inst)) goto handled;
 
-        fprintf(stderr, "___Unrecognized Instruction___");
-    handled:
+        if (inst.bytes_read > 0)
+        {
+            decode_instruction(inst_str_buf, inst);
+            printf("%s", inst_str_buf);
+            bytes_processed += inst.bytes_read;
+        }
+        else
+        {
+            bytes_processed += 1;
+            fprintf(stderr, "___Unrecognized Instruction___");
+        }
+    // handled:
         printf("\n");
     }
+    free(inst_str_buf);
+    free(buffer);
 }

lib.h

@@ -23,7 +23,7 @@ enum OptionTag {NONE, SOME};
         enum OptionTag tag;                                             \
         union {                                                         \
             char none;                                                  \
-            type some;                                                  \
+            type value;                                                  \
         };                                                              \
     } type##_opt;                                                       \
                                                                         \
@@ -34,13 +34,13 @@ enum OptionTag {NONE, SOME};
                                                                         \
     static inline type##_opt some_##type(type value)                    \
     {                                                                   \
-        return (type##_opt){ .tag = SOME, .some = value };              \
+        return (type##_opt){ .tag = SOME, .value = value };              \
     }                                                                   \
                                                                         \
     static inline int get_some_##type(type##_opt opt, type* out_value)  \
     {                                                                   \
         if (opt.tag != SOME) return 0;                                  \
-        *out_value = opt.some;                                          \
+        *out_value = opt.value;                                          \
         return 1;                                                       \
     }
 
@@ -50,3 +50,4 @@ enum OptionTag {NONE, SOME};
 
 
 OPTION(u8)
+OPTION(u16)