64-bit DLL compiled by G++ failed to load. #108
Description
I have a 64-bit DLL, with this source code:
#include <iostream>
extern "C"
{
__declspec(dllexport) __cdecl void Greet()
{
std::cout << "Hello World!" << std::endl;
}
__declspec(dllexport) __cdecl int addNumbers(int a, int b)
{
std::cout << "Adding " << a << " and " << b << "..." << std::endl;
return a + b;
}
}I compiled this using g++, downloadable from here.
This is my g++ version
g++ (MinGW-W64 x86_64-posix-seh, built by Brecht Sanders) 11.1.0 Copyright (C) 2021 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.This is the command I used:
g++ SampleDll.cpp -o SampleDLL.dll --shared
I. Attempt to load from file.
I have a C source file (always compiled using g++ Test.c MemoryModule.c -o Test.exe -D_WIN64)
and copied the whole LoadFromFile function from the demo to my source file:
The source
void LoadFromFile(void)
{
addNumberProc addNumber;
HRSRC resourceInfo;
DWORD resourceSize;
LPVOID resourceData;
TCHAR buffer[100];
HINSTANCE handle = LoadLibrary(DLL_FILE);
if (handle == NULL)
return;
addNumber = (addNumberProc)GetProcAddress(handle, "addNumbers");
_tprintf(_T("From file: %d\n"), addNumber(1, 2));
resourceInfo = FindResource(handle, MAKEINTRESOURCE(VS_VERSION_INFO), RT_VERSION);
_tprintf(_T("FindResource returned 0x%p\n"), resourceInfo);
resourceSize = SizeofResource(handle, resourceInfo);
resourceData = LoadResource(handle, resourceInfo);
_tprintf(_T("Resource data: %ld bytes at 0x%p\n"), resourceSize, resourceData);
LoadString(handle, 1, buffer, sizeof(buffer));
_tprintf(_T("String1: %s\n"), buffer);
LoadString(handle, 20, buffer, sizeof(buffer));
_tprintf(_T("String2: %s\n"), buffer);
FreeLibrary(handle);
}It loads properly:
Adding 1 and 2...
From file: 3
FindResource returned 0x0000000000000000
Resource data: 0 bytes at 0x0000000000000000
String1:
String2:
II. Attempt to load from Memory
I also copied the LoadFromMemory and the ReadLibrary function:
The source
void* ReadLibrary(size_t* pSize) {
size_t read;
void* result;
FILE* fp;
fp = _tfopen(DLL_FILE, _T("rb"));
if (fp == NULL)
{
_tprintf(_T("Can't open DLL file \"%s\"."), DLL_FILE);
return NULL;
}
fseek(fp, 0, SEEK_END);
*pSize = (size_t)(ftell(fp));
if (*pSize == 0)
{
fclose(fp);
return NULL;
}
result = (unsigned char *)malloc(*pSize);
if (result == NULL)
{
return NULL;
}
fseek(fp, 0, SEEK_SET);
read = fread(result, 1, *pSize, fp);
fclose(fp);
if (read != *pSize)
{
free(result);
return NULL;
}
return result;
}
void LoadFromMemory(void)
{
void *data;
size_t size;
HMEMORYMODULE handle;
addNumberProc addNumber;
HMEMORYRSRC resourceInfo;
DWORD resourceSize;
LPVOID resourceData;
TCHAR buffer[100];
data = ReadLibrary(&size);
if (data == NULL)
{
return;
}
handle = MemoryLoadLibrary(data, size);
if (handle == NULL)
{
_tprintf(_T("%i"), GetLastError());
_tprintf(_T("Can't load library from memory.\n"));
goto exit;
}
addNumber = (addNumberProc)MemoryGetProcAddress(handle, "addNumbers");
_tprintf(_T("From memory: %d\n"), addNumber(66, 99));
resourceInfo = MemoryFindResource(handle, MAKEINTRESOURCE(VS_VERSION_INFO), RT_VERSION);
_tprintf(_T("MemoryFindResource returned 0x%p\n"), resourceInfo);
resourceSize = MemorySizeofResource(handle, resourceInfo);
resourceData = MemoryLoadResource(handle, resourceInfo);
_tprintf(_T("Memory resource data: %ld bytes at 0x%p\n"), resourceSize, resourceData);
MemoryLoadString(handle, 1, buffer, sizeof(buffer));
_tprintf(_T("String1: %s\n"), buffer);
MemoryLoadString(handle, 20, buffer, sizeof(buffer));
_tprintf(_T("String2: %s\n"), buffer);
MemoryFreeLibrary(handle);
exit:
free(data);
}This time, the test program failed, with an access violation.
III. Attempt to use C#'s P/Invoke:
It just works, using a basic DllImport attribute.
IV. Attempt to use a translated MemoryModule version, from a managed executable:
Fails, for the same reason.
V. Some more stuff.
After using a C# debugger on the translated version, and various printf debugging on the original library, I found this line of code's the culprit:
BOOL successfull = (*DllEntry)((HINSTANCE)code, DLL_PROCESS_ATTACH, 0);
The access violation happened right after calling the dll entry point, and not because of a null pointer.
TL;DR
- I have a C++ dll, 64-bit, compiled using G++ on MinGW-w64, which is perfectly valid (
P/Invoke-able, andLoadLibrary-able). - Loading it using MemoryModule gives an Access Violation error when trying to call the dll entry point.
- Any other dll's (Compiled using MSVC (64-bit, or 32-bit), or using the lesser-known Orange C compiler (32-bit only)) works normally on MemoryModule.
I do not have any experience with such low level programming, please help me explain why MemoryModule crashed when calling this entry point. Thanks in advance.