crt0.c代码内容解释和编译器构造

下面用红色字体，做部分解释：

/***
2

*crt0.c - C runtime initialization routine
3

*
4

* Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
5

*
6

*Purpose:
7

* This the actual startup routine for apps. It calls the user's main
8

* routine [w]main() or [w]WinMain after performing C Run-Time Library
9

* initialization.
10

*
11

* (With ifdef's, this source file also provides the source code for
12

* wcrt0.c, the startup routine for console apps with wide characters,
13

* wincrt0.c, the startup routine for Windows apps, and wwincrt0.c,
14

* the startup routine for Windows apps with wide characters.)
15

*
16

*******************************************************************************/
17

#ifdef _WIN32
19

#ifndef CRTDLL
21

#include <cruntime.h>
23

#include <dos.h>
24

#include <internal.h>
25

#include <stdlib.h>
26

#include <string.h>
27

#include <rterr.h>
28

#include <windows.h>
29

#include <awint.h>
30

#include <tchar.h>
31

#include <dbgint.h>
32

/*
34

* wWinMain is not yet defined in winbase.h. When it is, this should be
35

* removed.
36

*/
37

int
39

WINAPI
40

wWinMain(
41

HINSTANCE hInstance,
42

HINSTANCE hPrevInstance,
43

LPWSTR lpCmdLine,
44

int nShowCmd
45

);
46

#ifdef WPRFLAG
48

_TUCHAR * __cdecl _wwincmdln(void);
49

#else /* WPRFLAG */
50

_TUCHAR * __cdecl _wincmdln(void);
51

#endif /* WPRFLAG */
52

/*
54

* command line, environment, and a few other globals
55

*/
56

#ifdef WPRFLAG
58

wchar_t *_wcmdln; /* points to wide command line */
59

#else /* WPRFLAG */
60

char *_acmdln; /* points to command line */
61

#endif /* WPRFLAG */
62

char *_aenvptr = NULL; /* points to environment block */
64

wchar_t *_wenvptr = NULL; /* points to wide environment block */
65

void (__cdecl * _aexit_rtn)(int) = _exit; /* RT message return procedure */
68

static void __cdecl fast_error_exit(int); /* Error exit via ExitProcess */
70

/*
72

* _error_mode and _apptype, together, determine how error messages are
73

* written out.
74

*/
75

int __error_mode = _OUT_TO_DEFAULT;
76

#ifdef _WINMAIN_
77

int __app_type = _GUI_APP;
78

#else /* _WINMAIN_ */
79

int __app_type = _CONSOLE_APP;
80

#endif /* _WINMAIN_ */
81

/***
84

*BaseProcessStartup(PVOID Peb)
85

*
86

*Purpose:
87

* This routine does the C runtime initialization, calls main(), and
88

* then exits. It never returns.
89

*
90

*Entry:
91

* PVOID Peb - pointer to Win32 Process Environment Block (not used)
92

*
93

*Exit:
94

* This function never returns.
95

*
96

*******************************************************************************/
97

#ifdef _WINMAIN_
99

100

#ifdef WPRFLAG
101

void wWinMainCRTStartup(
102

#else /* WPRFLAG */
103

void WinMainCRTStartup(
104

#endif /* WPRFLAG */
105

106

#else /* _WINMAIN_ */
107

108

#ifdef WPRFLAG
109

void wmainCRTStartup(
110

#else /* WPRFLAG */
111

void mainCRTStartup(
112

#endif /* WPRFLAG */
113

114

#endif /* _WINMAIN_ */
115

void
116

)
117

118

{
119

int mainret;
120

121

#ifdef _WINMAIN_
122

_TUCHAR *lpszCommandLine;
123

STARTUPINFO StartupInfo;
124

#endif /* _WINMAIN_ */
125

126

/*
127

* Get the full Win32 version
128

*/
129

_osver = GetVersion();
130

131

_winminor = (_osver >> 8) & 0x00FF ;
132

_winmajor = _osver & 0x00FF ;
133

_winver = (_winmajor << 8) + _winminor;
134

_osver = (_osver >> 16) & 0x00FFFF ;
135

136

#ifdef _MT
137

if ( !_heap_init(1) ) /* initialize heap */
138

#else /* _MT */
139

if ( !_heap_init(0) ) /* initialize heap */
140

#endif /* _MT */
141

fast_error_exit(_RT_HEAPINIT); /* write message and die */
142

143

#ifdef _MT
144

if( !_mtinit() ) /* initialize multi-thread */
145

fast_error_exit(_RT_THREAD); /* write message and die */
146

#endif /* _MT */
147

148

/*
149

* Guard the remainder of the initialization code and the call
150

* to user's main, or WinMain, function in a __try/__except
151

* statement.
152

*/
153

154

__try {
155

156

_ioinit(); /* initialize lowio */
157

158

#ifdef WPRFLAG
159

/* get wide cmd line info */
160

_wcmdln = (wchar_t *)__crtGetCommandLineW();
161

162

/* get wide environ info */
163

_wenvptr = (wchar_t *)__crtGetEnvironmentStringsW();
164

165

_wsetargv();
166

_wsetenvp();
167

#else /* WPRFLAG */
168

/* get cmd line info */
169

_acmdln = (char *)GetCommandLineA();
170

171

/* get environ info */
172

_aenvptr = (char *)__crtGetEnvironmentStringsA();
173

174

_setargv();
175

_setenvp();
176

#endif /* WPRFLAG */
177

178

_cinit(); /* do C data initialize */
179

180

#ifdef _WINMAIN_
181

182

StartupInfo.dwFlags = 0;
183

GetStartupInfo( &StartupInfo );
184

185

#ifdef WPRFLAG
186

lpszCommandLine = _wwincmdln();
187

mainret = wWinMain(
188

#else /* WPRFLAG */
189

lpszCommandLine = _wincmdln();
190

mainret = WinMain(
191

#endif /* WPRFLAG */
192

GetModuleHandleA(NULL),
193

NULL,
194

lpszCommandLine,
195

StartupInfo.dwFlags & STARTF_USESHOWWINDOW
196

? StartupInfo.wShowWindow
197

: SW_SHOWDEFAULT
198

);
199

#else /* _WINMAIN_ */
200

201

#ifdef WPRFLAG
202

__winitenv = _wenviron;
203

mainret = wmain(__argc, __wargv, _wenviron);
204

#else /* WPRFLAG */
205

__initenv = _environ;
206

mainret = main(__argc, __argv, _environ);
207

#endif /* WPRFLAG */
208

209

#endif /* _WINMAIN_ */
210

exit(mainret);
211

}
212

__except ( _XcptFilter(GetExceptionCode(), GetExceptionInformation()) )
213

{
214

/*
215

* Should never reach here
216

*/
217

_exit( GetExceptionCode() );
218

219

} /* end of try - except */
220

221

}
222

223

224

225

/***
226

*_amsg_exit(rterrnum) - Fast exit fatal errors
227

*
228

*Purpose:
229

* Exit the program with error code of 255 and appropriate error
230

* message.
231

*
232

*Entry:
233

* int rterrnum - error message number (amsg_exit only).
234

*
235

*Exit:
236

* Calls exit() (for integer divide-by-0) or _exit() indirectly
237

* through _aexit_rtn [amsg_exit].
238

* For multi-thread: calls _exit() function
239

*
240

*Exceptions:
241

*
242

*******************************************************************************/
243

244

void __cdecl _amsg_exit (
245

int rterrnum
246

)
247

{
248

#ifdef _WINMAIN_
249

if ( __error_mode == _OUT_TO_STDERR )
250

#else /* _WINMAIN_ */
251

if ( __error_mode != _OUT_TO_MSGBOX )
252

#endif /* _WINMAIN_ */
253

_FF_MSGBANNER(); /* write run-time error banner */
254

255

_NMSG_WRITE(rterrnum); /* write message */
256

_aexit_rtn(255); /* normally _exit(255) */
257

}
258

259

/***
260

*fast_error_exit(rterrnum) - Faster exit fatal errors
261

*
262

*Purpose:
263

* Exit the process with error code of 255 and appropriate error
264

* message.
265

*
266

*Entry:
267

* int rterrnum - error message number (amsg_exit only).
268

*
269

*Exit:
270

* Calls ExitProcess.
271

*
272

*Exceptions:
273

*
274

*******************************************************************************/
275

276

static void __cdecl fast_error_exit (
277

int rterrnum
278

)
279

{
280

#ifdef _WINMAIN_
281

if ( __error_mode == _OUT_TO_STDERR )
282

#else /* _WINMAIN_ */
283

if ( __error_mode != _OUT_TO_MSGBOX )
284

#endif /* _WINMAIN_ */
285

_FF_MSGBANNER(); /* write run-time error banner */
286

287

_NMSG_WRITE(rterrnum); /* write message */
288

ExitProcess(255); /* normally _exit(255) */
289

}
290

291

#ifndef WPRFLAG
292

293

294

#endif /* WPRFLAG */
295

296

#endif /* CRTDLL */
297

298

#else /* _WIN32 */
299

300

#include <cruntime.h>
301

#include <internal.h>
302

#include <stdlib.h>
303

#include <msdos.h>
304

#include <string.h>
305

#include <setjmp.h>
306

#include <dbgint.h>
307

#include <macos\types.h>
308

#include <macos\segload.h>
309

#include <macos\gestalte.h>
310

#include <macos\osutils.h>
311

#include <macos\traps.h>
312

#include <mpw.h>
313

314

static void __cdecl Inherit(void); /* local function */
315

316

int __cdecl main(int, char **, char **); /*generated by compiler*/
317

318

unsigned long _GetShellStack(void);
319

320

static char * __cdecl _p2cstr_internal ( unsigned char * str );
321

322

extern MPWBLOCK * _pMPWBlock;
323

extern int __argc;
324

extern char **__argv;
325

326

/***
327

*__crt0()
328

*
329

*Purpose:
330

* This routine does the C runtime initialization, calls main(), and
331

* then exits. It never returns.
332

*
333

*Entry:
334

*
335

*Exit:
336

* This function never returns.
337

*
338

*******************************************************************************/
339

340

void __cdecl __crt0 (
341

)
342

{
343

int mainret;
344

char szPgmName[32];
345

char *pArg;
346

char *argv[2];
347

348

#ifndef _M_MPPC
349

void *pv;
350

351

/* This is the magic stuff that MPW tools do to get info from MPW*/
352

353

pv = (void *)*(int *)0x316;
354

if (pv != NULL && !((int)pv & 1) && *(int *)pv == 'MPGM') {
355

pv = (void *)*++(int *)pv;
356

if (pv != NULL && *(short *)pv == 'SH') {
357

_pMPWBlock = (MPWBLOCK *)pv;
358

}
359

}
360

361

#endif /* _M_MPPC */
362

363

_environ = NULL;
364

if (_pMPWBlock == NULL) {
365

__argc = 1;
366

memcpy(szPgmName, (char *)0x910, sizeof(szPgmName));
367

pArg = _p2cstr_internal(szPgmName);
368

argv[0] = pArg;
369

argv[1] = NULL;
370

__argv = argv;
371

372

#ifndef _M_MPPC
373

_shellStack = 0; /* force ExitToShell */
374

#endif /* _M_MPPC */
375

}
376

#ifndef _M_MPPC
377

else {
378

_shellStack = _GetShellStack(); //return current a6, or first a6
379

_shellStack += 4; //a6 + 4 is the stack pointer we want
380

__argc = _pMPWBlock->argc;
381

__argv = _pMPWBlock->argv;
382

383

Inherit(); /* Inherit file handles - env is set up by _envinit if needed */
384

}
385

#endif /* _M_MPPC */
386

387

/*
388

* call run time initializer
389

*/
390

__cinit();
391

392

mainret = main(__argc, __argv, _environ);
393

exit(mainret);
394

}
395

396

397

#ifndef _M_MPPC
398

/***
399

*Inherit() - obtain and process info on inherited file handles.
400

*
401

*Purpose:
402

*
403

* Locates and interprets MPW std files. For files we just save the
404

* file handles. For the console we save the device table address so
405

* we can do console I/O. In the latter case, FDEV is set in the _osfile
406

* array.
407

*
408

*Entry:
409

* Address of MPW param table
410

*
411

*Exit:
412

* No return value.
413

*
414

*Exceptions:
415

*
416

*******************************************************************************/
417

418

static void __cdecl Inherit (
419

void
420

)
421

{
422

MPWFILE *pFile;
423

int i;
424

pFile = _pMPWBlock->pFile;
425

if (pFile == NULL) {
426

return;
427

}
428

for (i = 0; i < 3; i++) {
429

switch ((pFile->pDevice)->name) {
430

case 'ECON':
431

_osfile[i] |= FDEV | FOPEN;
432

_osfhnd[i] = (int)pFile;
433

break;
434

435

case 'FSYS':
436

_osfile[i] |= FOPEN;
437

_osfhnd[i] = (*(pFile->ppFInfo))->ioRefNum;
438

break;
439

}
440

pFile++;
441

}
442

}
443

444

#endif /* _M_MPPC */
445

446

447

448

static char * __cdecl _p2cstr_internal (
449

unsigned char * str
450

)
451

{
452

unsigned char *pchSrc;
453

unsigned char *pchDst;
454

int cch;
455

456

if ( str && *str ) {
457

pchDst = str;
458

pchSrc = str + 1;
459

460

for ( cch=*pchDst; cch; --cch ) {
461

*pchDst++ = *pchSrc++;
462

}
463

464

*pchDst = '\0';
465

}
466

467

return( str );
468

}
469

470

#endif /* _WIN32 */
471

1. 应用程序类型--------只有2类：要么是CUI，要么是GUI
2. 程序真正的启动代码（入口点函数）-----------各种**CRTStartUp
3. 环境变量+命令行信息的相关变量和函数都在此文件中有定义或声明
4. 调用运行时初始化+main()函数的最后返回和报错信息在下面的代码定义了

*******************************************************************************/
2

void __cdecl __crt0 (
4

)
5

{
6

int mainret;
7

char szPgmName[32];
8

char *pArg;
9

char *argv[2];
10

#ifndef _M_MPPC
12

void *pv;
13

/* This is the magic stuff that MPW tools do to get info from MPW*/
15

pv = (void *)*(int *)0x316;
17

if (pv != NULL && !((int)pv & 1) && *(int *)pv == 'MPGM') {
18

pv = (void *)*++(int *)pv;
19

if (pv != NULL && *(short *)pv == 'SH') {
20

_pMPWBlock = (MPWBLOCK *)pv;
21

}
22

}
23

#endif /* _M_MPPC */
25

_environ = NULL;
27

if (_pMPWBlock == NULL) {
28

__argc = 1;
29

memcpy(szPgmName, (char *)0x910, sizeof(szPgmName));
30

pArg = _p2cstr_internal(szPgmName);
31

argv[0] = pArg;
32

argv[1] = NULL;
33

__argv = argv;
34

#ifndef _M_MPPC
36

_shellStack = 0; /* force ExitToShell */
37

#endif /* _M_MPPC */
38

}
39

#ifndef _M_MPPC
40

else {
41

_shellStack = _GetShellStack(); //return current a6, or first a6
42

_shellStack += 4; //a6 + 4 is the stack pointer we want
43

__argc = _pMPWBlock->argc;
44

__argv = _pMPWBlock->argv;
45

Inherit(); /* Inherit file handles - env is set up by _envinit if needed */
47

}
48

#endif /* _M_MPPC */
49

/*
51

* call run time initializer
52

*/
53

__cinit();
54

mainret = main(__argc, __argv, _environ);
56

exit(mainret);
57

}
58

5. 获取进程信息+响应中断的代码如下：

/***
2

*Inherit() - obtain and process info on inherited file handles.
3

*
4

*Purpose:
5

*
6

* Locates and interprets MPW std files. For files we just save the
7

* file handles. For the console we save the device table address so
8

* we can do console I/O. In the latter case, FDEV is set in the _osfile
9

* array.
10

*
11

*Entry:
12

* Address of MPW param table
13

*
14

*Exit:
15

* No return value.
16

*
17

*Exceptions:
18

*
19

*******************************************************************************/
20

static void __cdecl Inherit (
22

void
23

)
24

{
25

MPWFILE *pFile;
26

int i;
27

pFile = _pMPWBlock->pFile;
28

if (pFile == NULL) {
29

return;
30

}
31

for (i = 0; i < 3; i++) {
32

switch ((pFile->pDevice)->name) {
33

case 'ECON':
34

_osfile[i] |= FDEV | FOPEN;
35

_osfhnd[i] = (int)pFile;
36

break;
37

case 'FSYS':
39

_osfile[i] |= FOPEN;
40

_osfhnd[i] = (*(pFile->ppFInfo))->ioRefNum;
41

break;
42

}
43

pFile++;
44

}
45

}
46

#endif /* _M_MPPC */
48

static char * __cdecl _p2cstr_internal (
52

unsigned char * str
53

)
54

{
55

unsigned char *pchSrc;
56

unsigned char *pchDst;
57

int cch;
58

if ( str && *str ) {
60

pchDst = str;
61

pchSrc = str + 1;
62

for ( cch=*pchDst; cch; --cch ) {
64

*pchDst++ = *pchSrc++;
65

}
66

*pchDst = '\0';
68

}
69

return( str );
71

}
72

#endif /* _WIN32 */

6. 如果是GUI程序，则要创建“内核对象”，请参考下面的MSDN中的STARTUPINFO结构体的说明
http://www.cnblogs.com/shanzy/articles/513455.html

7. 上面的crt0.c文件中涉及到MS针对不同的CPU厂商都能够跑MS的VC编译器的CPU假设，如下面MSDN文章所说------------当然，你也可以在代码中手写下面这些MS预定义宏，或者写MAKEFILE

Predefined Macros

The compiler recognizes six predefined ANSI C macros (see Table 1.1), and the Microsoft C++ implementation provides several more (see Table 1.2). These macros take no arguments and cannot be redefined. Their value (except for __LINE__ and __FILE__) must be constant throughout compilation. Some of the predefined macros listed below are defined with multiple values. Their values can be set by selecting the corresponding menu option in the Visual C++ development environment, or by using a command-line switch. See the tables below for more information.

Table 1.1 ANSI Predefined Macros

Macro	Description
__DATE__	The compilation date of the current source file. The date is a string literal of the form Mmm dd yyyy. The month name Mmm is the same as for dates generated by the library function asctime declared in TIME.H.
__FILE__	The name of the current source file. __FILE__ expands to a string surrounded by double quotation marks.
__LINE__	The line number in the current source file. The line number is a decimal integer constant. It can be altered with a #line directive.
__STDC__	Indicates full conformance with the ANSI C standard. Defined as the integer constant 1 only if the /Za compiler option is given and you are not compiling C++ code; otherwise is undefined.
__TIME__	The most recent compilation time of the current source file. The time is a string literal of the form hh:mm:ss.
__TIMESTAMP__	The date and time of the last modification of the current source file, expressed as a string literal in the form Ddd Mmm Date hh:mm:ss yyyy, where Ddd is the abbreviated day of the week and Date is an integer from 1 to 31.

Table 1.2 Microsoft-Specific Predefined Macros

Macro	Description
_CHAR_UNSIGNED	Default char type is unsigned. Defined when /J is specified.
__cplusplus	Defined for C++ programs only.
_CPPRTTI	Defined for code compiled with /GR (Enable Run-Time Type Information).
_CPPUNWIND	Defined for code compiled with /GX (Enable Exception Handling).
_DLL	Defined when /MD or /MDd (Multithread DLL) is specified.
_M_ALPHA	Defined for DEC ALPHA platforms. It is defined as 1 by the ALPHA compiler, and it is not defined if another compiler is used.
_M_IX86	Defined for x86 processors. See Table 1.3 for more details.
_M_MPPC	Defined for Power Macintosh platforms. Default is 601 (/QP601). See Table 1.4 for more details.
_M_MRX000	Defined for MIPS platforms. Default is 4000 (/QMR4000). See Table 1.5 for more details.
_M_PPC	Defined for PowerPC platforms. Default is 604 (/QP604). See Table 1.6 for more details.
_MFC_VER	Defines the MFC version. Defined as 0x0421 for Microsoft Foundation Class Library 4.21. Always defined.
_MSC_EXTENSIONS	This macro is defined when compiling with the /Ze compiler option (the default). Its value, when defined, is 1.
_MSC_VER	Defines the compiler version. Defined as 1200 for Microsoft Visual C++ 6.0. Always defined.
_MT	Defined when /MD or /MDd (Multithreaded DLL) or /MT or /MTd (Multithreaded) is specified.
_WIN32	Defined for applications for Win32®. Always defined.

As shown in following tables, the compiler generates a value for the preprocessor identifiers that reflect the processor option specified.

Table 1.3 Values for _M_IX86

Option in Developer Studio	Command-Line Option	Resulting Value
Blend	/GB	_M_IX86 = 500 (Default. Future compilers will emit a different value to reflect the dominant processor.)
Pentium	/G5	_M_IX86 = 500
Pentium Pro	/G6	_M_IX86 = 600
80386	/G3	_M_IX86 = 300
80486	/G4	_M_IX86 = 400

Table 1.4 Values for _M_MPPC

Option in development environment	Command-Line Option	Resulting Value
PowerPC 601	/QP601	_M_MPPC = 601 (Default)
PowerPC 603	/QP603	_M_MPPC = 603
PowerPC 604	/QP604	_M_MPPC = 604
PowerPC 620	/QP620	_M_MPPC = 620

Table 1.5 Values for _M_MRX000

Option in Developer Studio	Command-Line Option	Resulting Value
R4000	/QMR4000	_M_MRX000 = 4000 (Default)
R4100	/QMR4100	_M_MRX000 = 4100
R4200	/QMR4200	_M_MRX000 = 4200
R4400	/QMR4400	_M_MRX000 = 4400
R4600	/QMR4600	_M_MRX000 = 4600
R10000	/QMR10000	_M_MRX000 = 10000

Table 1.6 Values for _M_PPC

Option in Developer Studio	Command-Line Option	Resulting Value
PowerPC 601	/QP601	_M_PPC = 601
PowerPC 603	/QP603	_M_PPC = 603
PowerPC 604	/QP604	_M_PPC = 604 (Default)
PowerPC 620	/QP620	_M_PPC = 620

8. 任何C/C++编译器的构造，都是依托于ANSI C/ANSI C++标准的，但是，由于某些历史问题当ANSI标准影响了厂商的标准，或者厂商认为某些东西更利于开发的时候，厂商会在ANSI标准提供的编译器的基础上对CRT运行时库进行扩充，扩充的结果就是上面的情况

9. 厂商扩充了ANSI标准，就需要写出一个自己的编译器(MS 的VC编译器就是cl.exe)，写这个cl.exe的过程要根据厂商扩充之后的各种标准表格，在写这个cl.exe的时候做出很多的选择分支(当然，MS这里用它认为重要的一些“自定义宏”来写它的cl.exe)

posted @ 2006-09-24 17:45 -> 阅读(2333) 评论(0) 收藏举报

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