编译器链接启动代码crtexe.c

你是否想过为什么有时候main（）函数是入口地址，在win32中winmain()函数又是入口地址，其实是编译器在动态链接到crt[C runtime library(part of the C standard library)]时候设置的

程序设置断点，我们来看crtexe.c代码

第一个static int __cdecl pre_c_init(void)

*       The code in mainCRTStartup that was executed before executing C   initializers was shifted in this function. Also this funciton is the   first thing that is executed in c init section.

什么意思不用详细说，老外的注释很给力

static int __cdecl pre_c_init(void)
{
/*
* Determine if this is a managed application
*/
managedapp = check_managed_app();

/*
* Set __app_type properly
*/
#ifdef _WINMAIN_ //根据WINMAIN宏来设置应用程序是GUI程序还是控制台程序
__set_app_type(_GUI_APP);
#else /* _WINMAIN_ */
__set_app_type(_CONSOLE_APP);
#endif /* _WINMAIN_ */

/*
* Mark this module as an EXE file so that atexit/_onexit
* will do the right thing when called, including for C++
* d-tors.
*/
__onexitbegin = __onexitend = (_PVFV *)_encode_pointer((_PVFV *)(-1));

/*
* Propogate the _fmode and _commode variables to the DLL
*/
*_IMP___FMODE = _fmode;
*_IMP___COMMODE = _commode;

#ifdef _M_IX86
/*
* Set the local copy of the Pentium FDIV adjustment flag
*/

_adjust_fdiv = * _imp___adjust_fdiv;
#endif /* _M_IX86 */

/*
* Run the RTC initialization code for this DLL
*/
#ifdef _RTC
_RTC_Initialize();
#endif /* _RTC */

/*
* Call _setargv(), which will trigger a call to __setargv() if
* SETARGV.OBJ is linked with the EXE. If SETARGV.OBJ is not
* linked with the EXE, a dummy _setargv() will be called.
*/
#ifdef WPRFLAG
_wsetargv();
#else /* WPRFLAG */
_setargv();
#endif /* WPRFLAG */

/*
* If the user has supplied a _matherr routine then set
* __pusermatherr to point to it.
*/
if ( !__defaultmatherr )
__setusermatherr(_matherr);

#ifdef _M_IX86
_setdefaultprecision();
#endif /* _M_IX86 */

/* Enable per-thread locale if user asked for it */
if(__globallocalestatus == -1)
{
_configthreadlocale(-1);
}

return 0;
}这个函数在crt0dat.c中被调用，详细介绍，略去
第二个函数static void __cdecl pre_cpp_init(void)

static void __cdecl pre_cpp_init(void)
{
#ifdef _RTC
atexit(_RTC_Terminate);  //注册程序退出时的清理工
#endif  /* _RTC */

/*
* Get the arguments for the call to main. Note this must be
* done explicitly, rather than as part of the dll's
* initialization, to implement optional expansion of wild
* card chars in filename args
*/

startinfo.newmode = _newmode;

#ifdef WPRFLAG
argret = __wgetmainargs(&argc, &argv, &envp,
_dowildcard, &startinfo);
#else  /* WPRFLAG */
argret = __getmainargs(&argc, &argv, &envp,
_dowildcard, &startinfo);
#endif  /* WPRFLAG */

#ifndef _SYSCRT
if (argret < 0)
_amsg_exit(_RT_SPACEARG);
#endif  /* _SYSCRT */
}

下面是程序的第一个入口处
static
int
__tmainCRTStartup(
void
);

#ifdef _WINMAIN_

#ifdef WPRFLAG
int wWinMainCRTStartup(
#else /* WPRFLAG */
int WinMainCRTStartup(
#endif /* WPRFLAG */

#else /* _WINMAIN_ */

#ifdef WPRFLAG
int wmainCRTStartup(
#else /* WPRFLAG */
int mainCRTStartup(
#endif /* WPRFLAG */

#endif /* _WINMAIN_ */
void
)
{
/*
* The /GS security cookie must be initialized before any exception
* handling targetting the current image is registered. No function
* using exception handling can be called in the current image until
* after __security_init_cookie has been called.
*/
__security_init_cookie();

return __tmainCRTStartup();
}

/***

*mainCRTStartup(void)

*wmainCRTStartup(void)

*WinMainCRTStartup(void)

*wWinMainCRTStartup(void)

*

*Purpose:

*       These routines do the C runtime initialization, call the appropriate

*       user entry function, and handle termination cleanup.  For a managed

*       app, they then return the exit code back to the calling routine, which

*       is the managed startup code.  For an unmanaged app, they call exit and

*       never return.

*

*       Function:               User entry called:

*       mainCRTStartup          main

*       wmainCRTStartup         wmain

*       WinMainCRTStartup       WinMain

*       wWinMainCRTStartup      wWinMain
就是为程序找到入口地址，具体的判断是在函数__tmainCRTStartup()中
关键代码：

#ifdef WPRFLAG
mainret = wWinMain(
#else /* WPRFLAG */
mainret = WinMain(
#endif /* WPRFLAG */
(HINSTANCE)&__ImageBase,
NULL,
lpszCommandLine,
StartupInfo.dwFlags & STARTF_USESHOWWINDOW
? StartupInfo.wShowWindow
: SW_SHOWDEFAULT
);
#else /* _WINMAIN_ */

#ifdef WPRFLAG
__winitenv = envp;
mainret = wmain(argc, argv, envp);
#else /* WPRFLAG */
__initenv = envp;
mainret = main(argc, argv, envp);
#endif /* WPRFLAG */

#endif /* _WINMAIN_ */

我们看到，根据宏WPRFLAG来判断是wWinmain（）还是WinMain()，根据_WINMAIN_来判断入口函数是main（），wmain（）还是WinMain(),wWinMain()
wmain()和wWinMain(）是unicode版的，main()和WinMain()是ANSI版的 不过在程序中始终没有找到宏WPRFLAG是在哪里定义的，有空了再详细研究

然后就找到对应的入口程序执行。