Re: [Mingw-users] build dll without c runtime dependency

[Codeplug <gra...@ch...>]

chris wrote:
 > Hello,
 >
 > I'm using the following command to build a .dll without the C runtime
 > dependency (or any dependency for that matter):
 >
 > g++ -Wl,--subsystem,console -nodefaultlibs -nostartfiles -shared -s -o
 > mydll.dll main.o
 >
 > However, the following warning is issued:
 >
 > ld.exe: warning: cannot find entry symbol _DllMainCRTStartup@12;
 > defaulting to 10001000
 >
 > In main.cpp, this exists:
 >
 > extern "C" BOOL WINAPI _DllMainCRTStartup(HINSTANCE hinstDLL, DWORD
 > fdwReason, LPVOID lpvReserved) { return TRUE; }
 >

"WINAPI" typically resolves to __stdcall. Both MSVC and MinGW will 
decorate the names with a leading underscore and trailing @N. (NOTE: 
MinGW will omit the leading underscore for __stdcall when exporting from 
a dll - for some reason - which doesn't really apply here.)

 > This works under MSVC.
 >
 > To make this work in MinGW, I have to declare the function like such:
 >
 > extern "C" BOOL WINAPI DllMainCRTStartup(HINSTANCE hinstDLL, DWORD
 > fdwReason, LPVOID lpvReserved) { return TRUE; }
 >
 > (ie without the prefix underscore)
 >
 > It is not desirable to have to change the .cpp code depending if it is
 > built for MinGW or MSVC.
 >
 > Do note, that MSVC gives this error if the that function does not exist
 > as it is supposed to be named:
 >
 > LINK : error LNK2001: unresolved external symbol __DllMainCRTStartup@12
 >
 > Can anyone shed some light onto this discrepancy between MSVC and MinGW
 > and available solutions or workarounds at the tool level?
 >
 > Thanks.
 >
 > chris

The MS-CRT declares: "BOOL WINAPI _DllMainCRTStartup" (which "C" 
linkage), which yields a decorated name of "__DllMainCRTStartup@12". 
However, the default entry point for MinGW seems to be 
"_DllMainCRTStartup@12" - thus your issue.

What I would do is just use "DllMain", then use command line options to 
specify the entry point to use.

Here's what I used to link C++ code without a CRT under MinGW:
compile: "-fno-exceptions -fno-rtti"
link: "-mdll -entry=_DllMain@12 -lkernel32 -nostdlib"

Are you sure you want to run with no CRT under C++? You won't have 
global constructors/destructors (link error if you have any) and no 
exceptions and no RTTI...

gg