【Collection】Start function

When writing a Win32 application, a WinMain function must be implemented in the source code. But Windows program execution does not start from the WinMain function. The first thing to be executed is the code related to the startup function, which is generated by the compiler. The startup code completes the initialization process, and then calls the WinMain function.

 

For Visual C++ programs, it calls the C/C++ runtime startup function, which is responsible for initializing the C/C++ runtime library. Visual C++ is equipped with the source code of the C runtime library, the source code of the startup function can be found in the crtsrccrt0.c file (Visual C++ must select the option to install the source code during installation); and the startup code for the console program is stored in crtsrcwincmdln. c file.

All C/C++ runtime startup functions do basically the same thing: retrieve the command line pointer to the new process, retrieve the environment variable pointer to the new process, initialize global variables, initialize the memory stack, etc. When all initialization operations are complete, the startup function calls the application's entry point function. Calling the WinMain function looks like this:

 

 

When the entry point returns, the startup function calls the exit function of the C runtime library, passes the return value (nMainRetVal) to it, performs some necessary processing, and finally calls the system function ExitProcess to exit.

The following is a program compiled by Visual C++. The assembly code of the program startup code is as follows: