/Gh (Enable _penter hook function)

Causes a call to the _penter function at the start of every method or function.

Syntax

/Gh

Remarks

The _penter function isn't part of any library. It's up to you to provide a definition for _penter.

Unless you plan to explicitly call _penter, you don't need to provide a prototype. The function must push the content of all registers on entry and pop the unchanged content on exit. It must appear as if it had the following prototype:

void __declspec(naked) __cdecl _penter( void );

This declaration isn't available for 64-bit projects.

To set this compiler option in the Visual Studio development environment

1. Open the project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.

2. Select the Configuration Properties > C/C++ > Command Line property page.

3. Enter the compiler option in the Additional Options box.

To set this compiler option programmatically

• See AdditionalOptions.

Example

The following code, when compiled with /Gh, shows how _penter is called twice; once when entering function main and once when entering function x. The example consists of two source files, which you compile separately.

Source file local_penter.cpp:

// local_penter.cpp
// compile with: cl /EHsc /c local_penter.cpp
// processor: x86
#include <stdio.h>

extern "C" void __declspec(naked) __cdecl _penter( void ) {
   _asm {
      push eax
      push ebx
      push ecx
      push edx
      push ebp
      push edi
      push esi
    }

   printf_s("\nIn a function!");

   _asm {
      pop esi
      pop edi
      pop ebp
      pop edx
      pop ecx
      pop ebx
      pop eax
      ret
    }
}

Source file Gh_compiler_option.cpp:

// Gh_compiler_option.cpp
// compile with: cl /EHsc /Gh Gh_compiler_option.cpp local_penter.obj
// processor: x86
#include <stdio.h>

void x() {}

int main() {
   x();
}

When run, the local _penter function is called on entry to main and x:

In a function!
In a function!

See also

MSVC compiler options
MSVC compiler command-line syntax
/GH (Enable _pexit hook function)