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68 daniel-mar 1 
unit PatchU;
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81 daniel-mar 3 
{$WARN UNSAFE_CODE OFF}
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{$WARN UNSAFE_TYPE OFF}
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68 daniel-mar 6 
interface
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type
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  pPatchEvent = ^TPatchEvent;
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  // "Asm" opcode hack to patch an existing routine
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  TPatchEvent = packed record
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    Jump: Byte;
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    Offset: Integer;
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  end;
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  TPatchMethod = class
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  private
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    PatchedMethod, OriginalMethod: TPatchEvent;
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    PatchPositionMethod: pPatchEvent;
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    FIsPatched: boolean;
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  public
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    property IsPatched: boolean read FIsPatched;
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    constructor Create(const aSource, aDestination: Pointer);
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    destructor Destroy; override;
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    procedure Restore;
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    procedure Hook;
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  end;
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implementation
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uses
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  Windows, Sysutils;
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{ TPatchMethod }
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constructor TPatchMethod.Create(const aSource, aDestination: Pointer);
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var
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  OldProtect: Cardinal;
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begin
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  PatchPositionMethod := pPatchEvent(aSource);
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  OriginalMethod := PatchPositionMethod^;
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  PatchedMethod.Jump := $E9;
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  PatchedMethod.Offset := Integer(PByte(aDestination)) - Integer(PByte(PatchPositionMethod)) - SizeOf(TPatchEvent);
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  if not VirtualProtect(PatchPositionMethod, SizeOf(TPatchEvent), PAGE_EXECUTE_READWRITE, OldProtect) then
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    RaiseLastOSError;
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  Hook;
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end;
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destructor TPatchMethod.Destroy;
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begin
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  Restore;
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  inherited;
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end;
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procedure TPatchMethod.Hook;
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begin
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  if FIsPatched then Exit;
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  FIsPatched := true;
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  PatchPositionMethod^ := PatchedMethod;
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end;
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procedure TPatchMethod.Restore;
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begin
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  if not FIsPatched then Exit;
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  FIsPatched := false;
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  PatchPositionMethod^ := OriginalMethod;
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end;
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end.
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