HookLib with lable dynamic code generating

#include<windows.h>
#include<stdio.h>
#include<libdasm.h>

#pragma comment(lib, "libdasm.lib")

int inst_len = 0;
FARPROC hAPI=NULL;
char *szInstruction=NULL;
PDWORD pHookFuncAddr;

void MB(LPTSTR pszInfo)
{
MessageBox(NULL, pszInfo, TEXT("alert"), MB_OK);
}

BOOL fRet=FALSE;
DWORD temp;

void __declspec(naked) HookFunc()
{
__asm
{
pushad
pushfd
}

__asm
{
lea eax, APISub
mov temp, eax
}

OutputDebugString(TEXT("This call comes from hookfunc\n"));

fRet=WriteProcessMemory(GetCurrentProcess(), (PVOID)temp, szInstruction,
inst_len, NULL);
if(!fRet)
{
printf("WriteProcessMemory failed with error %d", GetLastError());
}

hAPI=(FARPROC)((DWORD)hAPI+inst_len);

__asm
{
popfd
popad
}

APISub:
__asm
{
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
__emit 0x90
jmp hAPI
}
}

BOOL StartHook()
{
INSTRUCTION inst;
BOOL fRet=FALSE, fOk=FALSE;
int len, lenlimit=6;
BYTE *buf=(BYTE *)hAPI;
char szError[100];
char *newcode=NULL;

__try
{
do {
len = get_instruction(&inst, buf+inst_len, MODE_32);
inst_len += len;
} while (inst_len < lenlimit);

newcode=new char[inst_len];
if(NULL==newcode)
{
sprintf(szError, "new newcode fails with %d",GetLastError());
MB(szError);
__leave;
}

memset(newcode,0x90, inst_len);
newcode[0]=0xff;
newcode[1]=0x25;
newcode[2]=0x11;
newcode[3]=0x22;
newcode[4]=0x33;
newcode[5]=0x44;

pHookFuncAddr=(PDWORD)HookFunc;
*(PDWORD)&newcode[2]=(DWORD)(&pHookFuncAddr);

szInstruction=new char[inst_len];
if(NULL==newcode)
{
sprintf(szError, "new szInstruction fails with %d",GetLastError());
MB(szError);
__leave;
}

fRet=ReadProcessMemory(GetCurrentProcess(), hAPI, szInstruction, inst_len, NULL);
if(!fRet)
{
sprintf(szError, "ReadProcessMemory fails with %d",GetLastError());
MB(szError);
__leave;
}

fRet=WriteProcessMemory(GetCurrentProcess(), hAPI, newcode,
inst_len, NULL);
if(!fRet)
{
sprintf(szError, "WriteProcessMemory fails with %d",GetLastError());
MB(szError);
__leave;
}
fOk=TRUE;
}
__finally
{
delete[] newcode;
}
return fOk;
}

BOOL WINAPI DllMain(
HINSTANCE hinstDLL,
DWORD fdwReason,
LPVOID lpvReserved
)
{
HANDLE hFileMapping=FALSE;
PVOID pView=NULL;
TCHAR szModule[50], szAPI[50];
HINSTANCE hModule=NULL;

char szError[100];
switch(fdwReason)
{
case DLL_PROCESS_ATTACH:
__try
{
hFileMapping=OpenFileMapping(FILE_MAP_READ|FILE_MAP_WRITE, FALSE, TEXT("APISPY1.0"));
if(NULL==hFileMapping)
{
sprintf(szError, "OpenFileMapping fails with %d",GetLastError());
MB(szError);
__leave;
}

pView=MapViewOfFile(hFileMapping, FILE_MAP_WRITE, 0, 0, 0);
if(NULL==pView)
{
sprintf(szError, "MapViewOfFile fails with %d",GetLastError());
MB(szError);
__leave;
}

CopyMemory(szModule, pView, sizeof(szModule));
CopyMemory(szAPI, (PBYTE)pView+sizeof(szModule), sizeof(szAPI));

hModule=GetModuleHandle(szModule);
if(NULL==hModule)
{
sprintf(szError, "GetModuleHandle fails with %d",GetLastError());
MB(szError);
__leave;
}
hAPI=GetProcAddress(hModule, szAPI);
if(NULL==hAPI)
{
sprintf(szError, "GetProcAddress fails with %d",GetLastError());
MB(szError);
__leave;
}

StartHook();
}
__finally
{
if(pView!=NULL)
{
UnmapViewOfFile(pView);
}
if(hFileMapping!=NULL)
{
CloseHandle(hFileMapping);
}
}
break;
case DLL_PROCESS_DETACH:
delete[] szInstruction;
break;
}
return TRUE;
}