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;
}