NSIS/Contrib/System/Source/System.h

// The following ifdef block is the standard way of creating macros which make exporting 
// from a DLL simpler. All files within this DLL are compiled with the SYSTEM_EXPORTS
// symbol defined on the command line. this symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see 
// SYSTEM_API functions as being imported from a DLL, whereas this DLL sees symbols
// defined with this macro as being exported.
#pragma once

#ifdef SYSTEM_EXPORTS
#define SYSTEM_API __declspec(dllexport)
#else
#define SYSTEM_API __declspec(dllimport)
#endif

#define NEW_STACK_SIZE     65536

// Proc types:
#define PT_NOTHING      0
#define PT_PROC         1
#define PT_STRUCT       2

// Proc results:
#define PR_OK           0
#define PR_ERROR        -1
#define PR_CALLBACK     1

// Real world argument types
#define	PAT_VOID		0
#define PAT_INT		    1
#define	PAT_LONG		2
#define PAT_STRING	    3
#define PAT_BOOLEAN	    4
#define PAT_CALLBACK    5

// Input/Output Source/Destination
#define	IOT_NONE    0
#define	IOT_STACK	-1
#define	IOT_REG		1
#define IOT_INLINE  (__INST_LAST+1) // should replace pointer to inline input
// #define INLINE_INPUT -> any other value, will contain pointer to input string

// Options
#define POPT_CDECL      0x1    // (Option & 0x1) == 0x1 -> cdecl, otherwise stdcall
#define POPT_PERMANENT  0x2    // Permanent proc, will not be destroyed after calling
#define POPT_ALWRETURN  0x4    // Always return
#define POPT_NEVERREDEF 0x8    // Never redefine
#define POPT_GENSTACK   0x10   // Use general stack (non temporary for callback)
#define POPT_CLONE      0x20   // This is clone callback

// Our single proc parameter
typedef struct
{
	int Type;
	int Option; // -1 -> Pointer, 1-... -> Special+1
	int Value;	// it can hold any 4 byte value 
    int _value; // value buffer for structures > 4 bytes (I hope 8 bytes will be enough)
    int Size; // Value real size (should be either 1 or 2 (the number of pushes))
    int Input;
	int Output;
} ProcParameter;

// Our single proc (Since the user will free proc with GlobalFree, 
// I've declared all variables as statics)
typedef struct tag_SystemProc SystemProc;
typedef struct tag_SystemProc
{
	int ProcType;
    int ProcResult;
    char DllName[1024];
    char ProcName[1024];
	HANDLE Dll;
	HANDLE Proc;
    int Options;
	int ParamCount;
	ProcParameter Params[100];	// I hope nobody will use more than 100 params

    // Callback specific
    int CallbackIndex;
    int ArgsSize;
    // Clone of current element (used for multi-level callbacks)
    SystemProc *Clone;
} SystemProc;

extern int ParamSizeByType[];   // Size of every parameter type (*4 bytes)

extern HANDLE CreateCallback(SystemProc *cbproc);
extern SystemProc *PrepareProc(BOOL NeedForCall);
extern void ParamAllocate(SystemProc *proc);
extern void ParamsDeAllocate(SystemProc *proc);
extern void ParamsIn(SystemProc *proc);
extern void ParamsOut(SystemProc *proc);
extern SystemProc *CallProc(SystemProc *proc);
extern SystemProc *CallBack(SystemProc *proc);
extern SystemProc *RealCallBack();
extern void CallStruct(SystemProc *proc);