checkpoint

1 files changed, 377 insertions, 0 deletions

diff --git a/src/sim86.cpp b/src/sim86.cpp
new file mode 100644
index 0000000..ba9e252
--- /dev/null
+++ b/src/sim86.cpp
@@ -0,0 +1,377 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "sim86.h"
+#include "sim86_shared.h"
+
+#include "generated/generated.cpp"
+
+global_variable u8 GlobalMemory[1*1024*1024] = {};
+
+internal void
+SetOrUnsetFlag(u32 *FlagsRegister, b32 Condition, flags_8086 Flag)
+{
+    if(Condition)
+    {
+        *FlagsRegister |= Flag;
+    }
+    else
+    {
+        *FlagsRegister &= (~Flag);
+    }
+}
+
+internal u32
+FlagsToString(char *Buffer, u32 Flags)
+{
+    u32 Length = 0;
+    
+    for(s32 MappingIndex = 0;
+        MappingIndex < flags_8086_strings_count;
+        MappingIndex++)
+    {
+        u8 Char = flags_8086_strings[MappingIndex][0];
+        b32 IsBitSet = (Flags & 1);
+        Flags >>= 1;
+        if(IsBitSet)
+        {
+            Buffer[Length++] = Char;
+        }
+    }
+    
+    return Length;
+}
+
+// Sets flags by checking the destination value of the register.
+internal void
+FlagsFromValue(u32 *FlagsRegister, u32 InstructionFlags, s32 Value)
+{
+    u32 OldFlagsRegister = *FlagsRegister;
+    
+    u32 SignMask = (1 << ((InstructionFlags & Inst_Wide) ? 15 : 7));
+    SetOrUnsetFlag(FlagsRegister, (Value & SignMask), Flag_Sign);
+    SetOrUnsetFlag(FlagsRegister, (Value == 0),       Flag_Zero);
+    
+    // NOTE(luca): Parity flag is set when in lower 8 bits have an even number of set bits.
+    u32 OneBitsCount = 0;
+    for(u32 BitsIndex = 0;
+        BitsIndex < 8;
+        BitsIndex++)
+    {
+        OneBitsCount += (Value & 1);
+        Value >>= 1;
+    }
+    SetOrUnsetFlag(FlagsRegister, (!(OneBitsCount & 1)), Flag_Parity);
+    
+    // TODO(luca): Overflow flag
+    // Were we adding positive numbers but produced a negative number?
+    
+    // TODO(luca): Carry flag 
+    // When twot numbers are added and the 17th bit would be set?
+    
+    // TODO(luca): Auxiliary carry flag
+    // Carry for bottom 8 bits
+    if(*FlagsRegister != OldFlagsRegister)
+    {
+        char OldFlagsString[ArrayCount(flags_8086_strings)] = {};
+        char FlagsString[ArrayCount(flags_8086_strings)] = {};
+        FlagsToString(OldFlagsString, OldFlagsRegister);
+        FlagsToString(FlagsString, *FlagsRegister);
+        
+        printf(" flags:%s->%s", OldFlagsString, FlagsString);
+    }
+}
+
+internal s32 *
+OperandToValue(s32 *Registers, u8 *Memory, instruction_operand *Operand)
+{
+    s32 *Result = 0;
+    
+    if(0) {}
+    else if(Operand->Type == Operand_Register)
+    {
+        Result = Registers + Operand->Register.Index;
+    }
+    else if(Operand->Type == Operand_Memory)
+    {
+        s32 CompleteDisplacement = Operand->Address.Displacement;
+        Assert(Operand->Address.Terms[0].Register.Count == Operand->Address.Terms[1].Register.Count);
+        
+        u32 Count = Operand->Address.Terms[0].Register.Count;
+        u32 Mask = ((u32)((-1)) >> (16 + (16 - Count*8)));
+        
+        CompleteDisplacement += 
+        (Registers[Operand->Address.Terms[0].Register.Index] & Mask) +
+        (Registers[Operand->Address.Terms[1].Register.Index] & Mask);
+        
+        Result = (s32 *)((u8 *)Memory + CompleteDisplacement);
+    }
+    else if(Operand->Type == Operand_Immediate)
+    {
+        Result = &Operand->Immediate.Value;
+    }
+    else if(Operand->Type != Operand_None)
+    {
+        Assert(0);
+    }
+    
+    return Result;
+}
+
+internal void
+Run8086(psize MemorySize, u8 *Memory)
+{
+    s32 Registers[Register_count] = {}; 
+    u32 FlagsRegister = 0;
+    u32 IPRegister = 0;
+    
+    while(IPRegister < MemorySize)
+    {
+        instruction Decoded;
+        Sim86_Decode8086Instruction(MemorySize - IPRegister, Memory + IPRegister, &Decoded);
+        if(Decoded.Op)
+        {
+            u32 OldIPRegister = IPRegister;
+            IPRegister += Decoded.Size;
+            
+#if SIM86_INTERNAL           
+            printf("Size:%u Op:%s Flags:0x%x ;", Decoded.Size, Sim86_MnemonicFromOperationType(Decoded.Op), Decoded.Flags);
+#endif
+            
+            instruction_operand *DestinationOperand = Decoded.Operands + 0;
+            instruction_operand *SourceOperand      = Decoded.Operands + 1;
+            
+            s32 *Destination = OperandToValue(Registers, Memory, DestinationOperand);
+            s32 *Source      = OperandToValue(Registers, Memory, SourceOperand);
+            
+            if(0) {}
+            else if(Decoded.Op == Op_int3)
+            {
+                Assert(0);
+            }
+            else if(Decoded.Op == Op_mov)
+            {
+                s32 Old = *Destination;
+                if(Decoded.Flags & Inst_Wide)
+                {
+                    *(u16 *)Destination = *(u16 *)Source;
+                }
+                else
+                {
+                    Assert((SourceOperand->Type == Operand_Immediate ||
+                            SourceOperand->Type == Operand_Memory) &&
+                           (SourceOperand->Register.Offset == 0));
+                    Assert((DestinationOperand->Type == Operand_Immediate || DestinationOperand->Type == Operand_Memory) && (DestinationOperand->Register.Offset == 0));
+                    
+                    u8 *SourceByte = (u8 *)Source + SourceOperand->Register.Offset;
+                    u8 *DestByte   = (u8 *)Destination + DestinationOperand->Register.Offset;
+                    
+                    *DestByte = *SourceByte;
+                }
+                
+#if SIM86_INTERNAL                    
+                if(DestinationOperand->Type == Operand_Register)
+                {
+                    printf(" %s:0x%x->0x%x", Sim86_RegisterNameFromOperand(&DestinationOperand->Register),
+                           Old, *Destination);
+                }
+#endif
+            }
+            else if(Decoded.Op == Op_cmp)
+            {
+                Assert(DestinationOperand->Type == Operand_Register);
+                Assert(SourceOperand->Type == Operand_Register || SourceOperand->Type == Operand_Immediate);
+                
+                s32 Value = ((Decoded.Flags & Inst_Wide) ? 
+                             (u16)((u16)*Destination - ((u16)*Source)) :
+                             (u8)((u8)*Destination - ((u8)*Source)));
+                
+                FlagsFromValue(&FlagsRegister, Decoded.Flags, Value);
+            }
+            else if(Decoded.Op == Op_sub)
+            {
+                Assert(DestinationOperand->Type == Operand_Register);
+                Assert(SourceOperand->Type == Operand_Register || SourceOperand->Type == Operand_Immediate);
+                
+                s32 Old = *Destination;
+                *Destination = ((Decoded.Flags & Inst_Wide) ? 
+                                (u16)((u16)*Destination - ((u16)*Source)) :
+                                (u8)((u8)*Destination - ((u8)*Source)));
+                
+                printf(" %s:0x%x->0x%x", 
+                       Sim86_RegisterNameFromOperand(&DestinationOperand->Register),
+                       Old, *Destination);
+                
+                FlagsFromValue(&FlagsRegister, Decoded.Flags, *Destination);
+                
+            }
+            else if(Decoded.Op == Op_add)
+            {
+                Assert(DestinationOperand->Type == Operand_Register);
+                
+                s32 Old = *Destination;
+                
+                *Destination = ((Decoded.Flags & Inst_Wide) ? 
+                                (u16)((u16)*Destination + ((u16)*Source)) :
+                                (u8)((u8)*Destination + ((u8)*Source)));
+                
+                printf(" %s:0x%x->0x%x", 
+                       Sim86_RegisterNameFromOperand(&DestinationOperand->Register),
+                       Old, *Destination);
+                
+                FlagsFromValue(&FlagsRegister, Decoded.Flags, *Destination);
+            }
+            else if(Decoded.Op == Op_jne)
+            {
+                if(!(FlagsRegister & Flag_Zero))
+                {
+                    IPRegister += *Destination;
+                }
+            }
+            else if(Decoded.Op == Op_je)
+            {
+                if((FlagsRegister & Flag_Zero))
+                {
+                    IPRegister += *Destination;
+                }
+            }
+            else
+            {
+                Assert(0 && "Op not implemented yet.");
+            }
+            
+#if SIM86_INTERNAL
+            printf(" ip:0x%x->0x%x", OldIPRegister, IPRegister);
+#endif
+            
+        }
+        else
+        {
+            printf("Unrecognized instruction\n");
+            break;
+        }
+        
+#if SIM86_INTERNAL
+        printf("\n");
+#endif
+        
+    }
+    
+    printf("Final registers:\n");
+    for(u32 RegisterIndex = Register_a;
+        RegisterIndex < Register_ds + 1;
+        RegisterIndex++)
+    {
+        register_access Register = {};
+        Register.Index = RegisterIndex;
+        Register.Offset = 0;
+        Register.Count = 2;
+        
+        u32 Value = Registers[RegisterIndex];
+        if(Value > 0)
+        {
+            printf("     %s: 0x%0x (%d)\n", 
+                   Sim86_RegisterNameFromOperand(&Register),
+                   Value, Value);
+        }
+    }
+    printf("     ip: 0x%04x (%d)\n", IPRegister, IPRegister);
+    
+    if(FlagsRegister)
+    {
+        char FlagsString[ArrayCount(flags_8086_strings)] = {};
+        FlagsToString(FlagsString, FlagsRegister);
+        printf("  flags: %s\n", FlagsString);
+    }
+}
+
+void PrintUsage(char *ExePath)
+{
+    printf("usage: %s [-exec] <assembly>\n", ExePath);
+}
+
+int main(int ArgsCount, char *Args[])
+{
+    u32 Version = Sim86_GetVersion();
+    
+#if SIM86_INTERNAL    
+    printf("Sim86 Version: %u (expected %u)\n", Version, SIM86_VERSION);
+#endif
+    
+    if(Version != SIM86_VERSION)
+    {
+        printf("ERROR: Header file version doesn't match DLL.\n");
+        return -1;
+    }
+    
+    instruction_table Table;
+    Sim86_Get8086InstructionTable(&Table);
+    
+#if SIM86_INTERNAL    
+    printf("8086 Instruction Instruction Encoding Count: %u\n", Table.EncodingCount);
+#endif
+    
+    // print (default)
+    // -exec (also execute the disassembled instructinos)
+    
+    b32 Execute = false;
+    b32 Dump = false;
+    char *FileName = 0;
+    for(s32 ArgsIndex = 1;
+        ArgsIndex < ArgsCount;
+        ArgsIndex++)
+    {
+        char *Command = Args[ArgsIndex];
+        if(0) {}
+        else if(!strcmp(Command, "-exec"))
+        {
+            Execute = true;
+        }
+        else if(!strcmp(Command, "-dump"))
+        {
+            Dump = true;
+        }
+        else 
+        {
+            FileName = Command;
+        }
+    }
+    
+    if(FileName)
+    {
+        FILE *File = fopen(FileName, "rb");
+        if(File)
+        {
+            psize BytesWritten = fread(GlobalMemory, 1, sizeof(GlobalMemory), File);
+            fclose(File);
+            
+            if(Execute)
+            {
+                printf("--- %s execution ---\n", FileName);
+                
+                Run8086(BytesWritten, GlobalMemory);
+                
+                if(Dump)
+                {
+                    // NOTE(luca): We have to add ".data" or Gimp will throw an error. 
+                    FILE *DumpFile = fopen("sim86_memory_0.data", "wb");
+                    fwrite(GlobalMemory, 1, sizeof(GlobalMemory), DumpFile);
+                    fclose(DumpFile);
+                }
+                
+            }
+            else
+            {
+                printf("ERROR: Disassembling not implemented yet.\n");
+            }
+            
+        }
+        else
+        {
+            printf("ERROR: Unable to open %s.\n", FileName);
+            PrintUsage(Args[0]);
+        }
+    }
+    
+    return 0;
+}