MinGW Main routine

Question

In C there is no main program. Sure, C programmers begin with int main(int argc char *argv[]), but this only works because there is a routine that tells the compiler/IDE to run the function named main first.

I can't seem to find this routine in MinGW, though. Where is it defined? I just searched because I wanted to change it (only as a test) and play around with it a bit. Can someone link me to the correct file in the MinGW folders?

Answer 1

The ld linker will look for a match of one of several symbols to use as the entry point when linking a PE file:

entry point              subsystem
---------------------   --------------

NtProcessStartup           native
WinMainCRTStartup          Windows GUI
mainCRTStartup             Windows CUI (console)
__PosixProcessStartup      POSIX CUI
WinMainCRTStartup          WinCE GUI
mainCRTStartup             Xbox
mainCRTStartup             other

DllMainCRTStartup@12 (or possibly DllMainCRTStartup) for DLLs

MinGW will have an object file that gets automatically linked in that has the actual PE entry point. - you can see what object files are being automatically linked in by using gcc's -v option.

In a quick test using MinGW 4.6.1 building a console subsystem "hello world" program, the object file containing the entry point is crt2.o and it has a symbol mainCRTStartup that is picked up by the linker as the entry point.

The source file containing the entrypoint code is crtexe.c (or crtdll.c).

You can override the entry point using the --entry option to the linker (Wl,--entry=whatever when used on the gcc command line).