windows-xp/Source/XPSP1/NT/base/mvdm/wow32/readit.txt

readme for interpreted thunks

Interpreted Thunks are an attempt to replace the simplest thunk functions
in WOW with a bit of data.  Each thunk consists of a pointer to the Win32
API routine (actually to a callable loader thunk in one of the pages set
aside for fixups if needed) and a pointer to a variable-length byte stream
which dictates how to convert arguments and return values.  The first byte
is an opcode indicating how to thunk the leftmost argument, the last byte
is distinguished by having its high bit set (0x8?) and indicates how to
thunk the return value.

A tool called genwowit reads a source file called wow.it which contains
psuedo-prototypes (really thunk descriptions) and generates wowit.h
and wowit.c with the actualy thunk table and assiociated instruction
"swamp" containing all the bytecode instruction streams.  See
\nt\private\sdktools\genwowit\readme.txt for details.

Note that the major restriction of interpreted thunks as implemented is
that pointers to structures which need thunking are not supported.

Here's a tiny wow.it and the wowit.h and wowit.c that result.

----- wow.it begin
INT   UpdateColors(HGDI);
INT   StartPage(HGDI);
INT   EndPage(HGDI);
DWORD GetFontData(HGDI, DWORD, DWORD, PTR, DWORD);
WORD  GetRasterizerCaps(PTR, INT);
WORD  IsGDIObject=GetObjectType(HGDI);
WORD  GetTextAlign(HGDI);
INT   GetTextCharacterExtra(HGDI);
INT   SetTextCharacterExtra(HGDI, INT);
DWORD GetTextColor(HGDI);
INT   GetTextFace(HGDI, INT, PTR);
INT   SetTextJustification(HGDI, INT, INT);
WORD  TextOut(HGDI, INT, INT, PTR, INT);
----- wow.it end

here's the output genwowit produces on the console:

Generated wowit.h and wowit.c from wow.it
13 thunks, 8 unique instruction streams, 29 instruction bytes, 5 max args.

And the files:

----- wowit.h begin
//
// wowit.h generated by genwowit.exe from wow.it, DO NOT EDIT.
//

#include "intthunk.h"

#define MAX_IT_ARGS  5

#define IT_WORD                 ( (UCHAR) 0x0 )
#define IT_INT                  ( (UCHAR) 0x1 )
#define IT_DWORD                ( (UCHAR) 0x2 )
#define IT_LPDWORD              ( (UCHAR) 0x3 )
#define IT_PTR                  ( (UCHAR) 0x4 )
#define IT_PTRORATOM            ( (UCHAR) 0x5 )
#define IT_HGDI                 ( (UCHAR) 0x6 )
#define IT_HUSER                ( (UCHAR) 0x7 )
#define IT_COLOR                ( (UCHAR) 0x8 )
#define IT_HINST                ( (UCHAR) 0x9 )
#define IT_HICON                ( (UCHAR) 0xa )
#define IT_16ONLY               ( (UCHAR) 0xb )
#define IT_32ONLY               ( (UCHAR) 0xc )

#define IT_RETMASK              ( (UCHAR) 0x80 )
#define IT_DWORDRET             ( IT_RETMASK | (UCHAR) 0x0 )
#define IT_WORDRET              ( IT_RETMASK | (UCHAR) 0x1 )
#define IT_INTRET               ( IT_RETMASK | (UCHAR) 0x2 )
#define IT_HGDIRET              ( IT_RETMASK | (UCHAR) 0x3 )
#define IT_HUSERRET             ( IT_RETMASK | (UCHAR) 0x4 )
#define IT_ZERORET              ( IT_RETMASK | (UCHAR) 0x5 )
#define IT_HICONRET             ( IT_RETMASK | (UCHAR) 0x6 )
#define IT_ONERET               ( IT_RETMASK | (UCHAR) 0x7 )
#define IT_HPRNDWPRET           ( IT_RETMASK | (UCHAR) 0x8 )

#define ITID_UpdateColors                             0
#define ITID_StartPage                                1
#define ITID_EndPage                                  2
#define ITID_GetFontData                              3
#define ITID_GetRasterizerCaps                        4
#define ITID_IsGDIObject                              5
#define ITID_GetTextAlign                             6
#define ITID_GetTextCharacterExtra                    7
#define ITID_SetTextCharacterExtra                    8
#define ITID_GetTextColor                             9
#define ITID_GetTextFace                              10
#define ITID_SetTextJustification                     11
#define ITID_TextOut                                  12

#define ITID_MAX 12
----- wowit.h end

----- wowit.c begin
//
// wowit.c generated by genwowit.exe from wow.it, DO NOT EDIT.
//

#include "precomp.h"
#pragma hdrstop
#define WOWIT_C
#include "wowit.h"

CONST BYTE InstrSwamp[] = {
    /*   0  0x0   */ IT_HGDI, IT_INTRET, 
    /*   1  0x2   */ IT_HGDI, IT_DWORD, IT_DWORD, IT_PTR, IT_DWORD, IT_DWORDRET, 
    /*   2  0x8   */ IT_HGDI, IT_INT, IT_INT, IT_PTR, IT_INT, IT_WORDRET, 
    /*   3  0xe   */ IT_HGDI, IT_WORDRET, 
    /*   4  0x10  */ IT_HGDI, IT_INT, IT_INTRET, 
    /*   5  0x13  */ IT_HGDI, IT_DWORDRET, 
    /*   6  0x15  */ IT_HGDI, IT_INT, IT_PTR, IT_INTRET, 
    /*   7  0x19  */ IT_HGDI, IT_INT, IT_INT, IT_INTRET, 
};

INT_THUNK_TABLEENTRY IntThunkTable[] = {
    /*   0 */ { (FARPROC) UpdateColors,                    InstrSwamp + 0x0    },  /* 0 */ 
    /*   1 */ { (FARPROC) StartPage,                       InstrSwamp + 0x0    },  /* 0 */ 
    /*   2 */ { (FARPROC) EndPage,                         InstrSwamp + 0x0    },  /* 0 */ 
    /*   3 */ { (FARPROC) GetFontData,                     InstrSwamp + 0x2    },  /* 1 */ 
    /*   4 */ { (FARPROC) GetRasterizerCaps,               InstrSwamp + 0xb    },  /* 2 + 3 */ 
    /*   5 */ { (FARPROC) GetObjectType,                   InstrSwamp + 0xe    },  /* 3 */ 
    /*   6 */ { (FARPROC) GetTextAlign,                    InstrSwamp + 0xe    },  /* 3 */ 
    /*   7 */ { (FARPROC) GetTextCharacterExtra,           InstrSwamp + 0x0    },  /* 0 */ 
    /*   8 */ { (FARPROC) SetTextCharacterExtra,           InstrSwamp + 0x10   },  /* 4 */ 
    /*   9 */ { (FARPROC) GetTextColor,                    InstrSwamp + 0x13   },  /* 5 */ 
    /*  10 */ { (FARPROC) GetTextFace,                     InstrSwamp + 0x15   },  /* 6 */ 
    /*  11 */ { (FARPROC) SetTextJustification,            InstrSwamp + 0x19   },  /* 7 */ 
    /*  12 */ { (FARPROC) TextOut,                         InstrSwamp + 0x8    },  /* 2 */ 
};
----- wowit.c end