操作系统实战45讲笔记-01 程序的运行过程：从代码到机器运行

计算机硬件是无法直接运行C 语言文本程序代码的，需要 C 语言编译器，把这个代码编译成具体硬件平台的二进制代码。再由具体操作系统建立进程，把这个二进制文件装进其进程的内存空间中，才能运行。

程序编译过程

示例代码：

经典Hello World C代码

#include "stdio.h"
int main(int argc, char const *argv[])
{
    printf("hello world!\n");
    return 0;
}

GCC 只是完成编译工作的驱动程序，它会根据编译流程分别调用预处理程序、编译程序、汇编程序、链接程序来完成具体工作

• gcc HelloWorld.c -E -o HelloWorld.i 预处理：加入头文件，替换宏。输出如下，

点击查看HelloWorld.i内容

xyjk1002@sheldon:~/cosmos/lesson01/HelloWorld$ cat HelloWorld.i
# 1 "HelloWorld.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<command-line>" 2
# 1 "HelloWorld.c"
# 1 "/usr/include/stdio.h" 1 3 4
# 27 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/libc-header-start.h" 1 3 4
# 33 "/usr/include/x86_64-linux-gnu/bits/libc-header-start.h" 3 4
# 1 "/usr/include/features.h" 1 3 4
# 424 "/usr/include/features.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 1 3 4
# 427 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4
# 428 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 2 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/long-double.h" 1 3 4
# 429 "/usr/include/x86_64-linux-gnu/sys/cdefs.h" 2 3 4
# 425 "/usr/include/features.h" 2 3 4
# 448 "/usr/include/features.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 1 3 4
# 10 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/gnu/stubs-64.h" 1 3 4
# 11 "/usr/include/x86_64-linux-gnu/gnu/stubs.h" 2 3 4
# 449 "/usr/include/features.h" 2 3 4
# 34 "/usr/include/x86_64-linux-gnu/bits/libc-header-start.h" 2 3 4
# 28 "/usr/include/stdio.h" 2 3 4
 
 
 
 
 
# 1 "/usr/lib/gcc/x86_64-linux-gnu/7/include/stddef.h" 1 3 4
# 216 "/usr/lib/gcc/x86_64-linux-gnu/7/include/stddef.h" 3 4
 
# 216 "/usr/lib/gcc/x86_64-linux-gnu/7/include/stddef.h" 3 4
typedef long unsigned int size_t;
# 34 "/usr/include/stdio.h" 2 3 4
 
# 1 "/usr/include/x86_64-linux-gnu/bits/types.h" 1 3 4
# 27 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/wordsize.h" 1 3 4
# 28 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4
 
 
typedef unsigned char __u_char;
typedef unsigned short int __u_short;
typedef unsigned int __u_int;
typedef unsigned long int __u_long;
 
 
typedef signed char __int8_t;
typedef unsigned char __uint8_t;
typedef signed short int __int16_t;
typedef unsigned short int __uint16_t;
typedef signed int __int32_t;
typedef unsigned int __uint32_t;
 
typedef signed long int __int64_t;
typedef unsigned long int __uint64_t;
 
 
 
 
 
 
 
typedef long int __quad_t;
typedef unsigned long int __u_quad_t;
 
 
 
 
 
 
 
typedef long int __intmax_t;
typedef unsigned long int __uintmax_t;
# 130 "/usr/include/x86_64-linux-gnu/bits/types.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/typesizes.h" 1 3 4
# 131 "/usr/include/x86_64-linux-gnu/bits/types.h" 2 3 4
 
 
typedef unsigned long int __dev_t;
typedef unsigned int __uid_t;
typedef unsigned int __gid_t;
typedef unsigned long int __ino_t;
typedef unsigned long int __ino64_t;
typedef unsigned int __mode_t;
typedef unsigned long int __nlink_t;
typedef long int __off_t;
typedef long int __off64_t;
typedef int __pid_t;
typedef struct { int __val[2]; } __fsid_t;
typedef long int __clock_t;
typedef unsigned long int __rlim_t;
typedef unsigned long int __rlim64_t;
typedef unsigned int __id_t;
typedef long int __time_t;
typedef unsigned int __useconds_t;
typedef long int __suseconds_t;
 
typedef int __daddr_t;
typedef int __key_t;
 
 
typedef int __clockid_t;
 
 
typedef void * __timer_t;
 
 
typedef long int __blksize_t;
 
 
 
 
typedef long int __blkcnt_t;
typedef long int __blkcnt64_t;
 
 
typedef unsigned long int __fsblkcnt_t;
typedef unsigned long int __fsblkcnt64_t;
 
 
typedef unsigned long int __fsfilcnt_t;
typedef unsigned long int __fsfilcnt64_t;
 
 
typedef long int __fsword_t;
 
typedef long int __ssize_t;
 
 
typedef long int __syscall_slong_t;
 
typedef unsigned long int __syscall_ulong_t;
 
 
 
typedef __off64_t __loff_t;
typedef char *__caddr_t;
 
 
typedef long int __intptr_t;
 
 
typedef unsigned int __socklen_t;
 
 
 
 
typedef int __sig_atomic_t;
# 36 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/types/__FILE.h" 1 3 4
 
 
 
struct _IO_FILE;
typedef struct _IO_FILE __FILE;
# 37 "/usr/include/stdio.h" 2 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/types/FILE.h" 1 3 4
 
 
 
struct _IO_FILE;
 
 
typedef struct _IO_FILE FILE;
# 38 "/usr/include/stdio.h" 2 3 4
 
 
 
# 1 "/usr/include/x86_64-linux-gnu/bits/libio.h" 1 3 4
# 35 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/_G_config.h" 1 3 4
# 19 "/usr/include/x86_64-linux-gnu/bits/_G_config.h" 3 4
# 1 "/usr/lib/gcc/x86_64-linux-gnu/7/include/stddef.h" 1 3 4
# 20 "/usr/include/x86_64-linux-gnu/bits/_G_config.h" 2 3 4
 
# 1 "/usr/include/x86_64-linux-gnu/bits/types/__mbstate_t.h" 1 3 4
# 13 "/usr/include/x86_64-linux-gnu/bits/types/__mbstate_t.h" 3 4
typedef struct
{
  int __count;
  union
  {
    unsigned int __wch;
    char __wchb[4];
  } __value;
} __mbstate_t;
# 22 "/usr/include/x86_64-linux-gnu/bits/_G_config.h" 2 3 4
 
 
 
 
typedef struct
{
  __off_t __pos;
  __mbstate_t __state;
} _G_fpos_t;
typedef struct
{
  __off64_t __pos;
  __mbstate_t __state;
} _G_fpos64_t;
# 36 "/usr/include/x86_64-linux-gnu/bits/libio.h" 2 3 4
# 53 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
# 1 "/usr/lib/gcc/x86_64-linux-gnu/7/include/stdarg.h" 1 3 4
# 40 "/usr/lib/gcc/x86_64-linux-gnu/7/include/stdarg.h" 3 4
typedef __builtin_va_list __gnuc_va_list;
# 54 "/usr/include/x86_64-linux-gnu/bits/libio.h" 2 3 4
# 149 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
struct _IO_jump_t; struct _IO_FILE;
 
 
 
 
typedef void _IO_lock_t;
 
 
 
 
 
struct _IO_marker {
  struct _IO_marker *_next;
  struct _IO_FILE *_sbuf;
 
 
 
  int _pos;
# 177 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
};
 
 
enum __codecvt_result
{
  __codecvt_ok,
  __codecvt_partial,
  __codecvt_error,
  __codecvt_noconv
};
# 245 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
struct _IO_FILE {
  int _flags;
 
 
 
 
  char* _IO_read_ptr;
  char* _IO_read_end;
  char* _IO_read_base;
  char* _IO_write_base;
  char* _IO_write_ptr;
  char* _IO_write_end;
  char* _IO_buf_base;
  char* _IO_buf_end;
 
  char *_IO_save_base;
  char *_IO_backup_base;
  char *_IO_save_end;
 
  struct _IO_marker *_markers;
 
  struct _IO_FILE *_chain;
 
  int _fileno;
 
 
 
  int _flags2;
 
  __off_t _old_offset;
 
 
 
  unsigned short _cur_column;
  signed char _vtable_offset;
  char _shortbuf[1];
 
 
 
  _IO_lock_t *_lock;
# 293 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
  __off64_t _offset;
 
 
 
 
 
 
 
  void *__pad1;
  void *__pad2;
  void *__pad3;
  void *__pad4;
 
  size_t __pad5;
  int _mode;
 
  char _unused2[15 * sizeof (int) - 4 * sizeof (void *) - sizeof (size_t)];
 
};
 
 
typedef struct _IO_FILE _IO_FILE;
 
 
struct _IO_FILE_plus;
 
extern struct _IO_FILE_plus _IO_2_1_stdin_;
extern struct _IO_FILE_plus _IO_2_1_stdout_;
extern struct _IO_FILE_plus _IO_2_1_stderr_;
# 337 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
typedef __ssize_t __io_read_fn (void *__cookie, char *__buf, size_t __nbytes);
 
 
 
 
 
 
 
typedef __ssize_t __io_write_fn (void *__cookie, const char *__buf,
     size_t __n);
 
 
 
 
 
 
 
typedef int __io_seek_fn (void *__cookie, __off64_t *__pos, int __w);
 
 
typedef int __io_close_fn (void *__cookie);
# 389 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
extern int __underflow (_IO_FILE *);
extern int __uflow (_IO_FILE *);
extern int __overflow (_IO_FILE *, int);
# 433 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
extern int _IO_getc (_IO_FILE *__fp);
extern int _IO_putc (int __c, _IO_FILE *__fp);
extern int _IO_feof (_IO_FILE *__fp) __attribute__ ((__nothrow__ , __leaf__));
extern int _IO_ferror (_IO_FILE *__fp) __attribute__ ((__nothrow__ , __leaf__));
 
extern int _IO_peekc_locked (_IO_FILE *__fp);
 
 
 
 
 
extern void _IO_flockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
extern void _IO_funlockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
extern int _IO_ftrylockfile (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
# 462 "/usr/include/x86_64-linux-gnu/bits/libio.h" 3 4
extern int _IO_vfscanf (_IO_FILE * __restrict, const char * __restrict,
   __gnuc_va_list, int *__restrict);
extern int _IO_vfprintf (_IO_FILE *__restrict, const char *__restrict,
    __gnuc_va_list);
extern __ssize_t _IO_padn (_IO_FILE *, int, __ssize_t);
extern size_t _IO_sgetn (_IO_FILE *, void *, size_t);
 
extern __off64_t _IO_seekoff (_IO_FILE *, __off64_t, int, int);
extern __off64_t _IO_seekpos (_IO_FILE *, __off64_t, int);
 
extern void _IO_free_backup_area (_IO_FILE *) __attribute__ ((__nothrow__ , __leaf__));
# 42 "/usr/include/stdio.h" 2 3 4
 
 
 
 
typedef __gnuc_va_list va_list;
# 57 "/usr/include/stdio.h" 3 4
typedef __off_t off_t;
# 71 "/usr/include/stdio.h" 3 4
typedef __ssize_t ssize_t;
 
 
 
 
 
 
typedef _G_fpos_t fpos_t;
# 131 "/usr/include/stdio.h" 3 4
# 1 "/usr/include/x86_64-linux-gnu/bits/stdio_lim.h" 1 3 4
# 132 "/usr/include/stdio.h" 2 3 4
 
 
 
extern struct _IO_FILE *stdin;
extern struct _IO_FILE *stdout;
extern struct _IO_FILE *stderr;
 
 
 
 
 
 
extern int remove (const char *__filename) __attribute__ ((__nothrow__ , __leaf__));
 
extern int rename (const char *__old, const char *__new) __attribute__ ((__nothrow__ , __leaf__));
 
 
 
extern int renameat (int __oldfd, const char *__old, int __newfd,
       const char *__new) __attribute__ ((__nothrow__ , __leaf__));
 
 
 
 
 
 
 
extern FILE *tmpfile (void) ;
# 173 "/usr/include/stdio.h" 3 4
extern char *tmpnam (char *__s) __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
 
 
extern char *tmpnam_r (char *__s) __attribute__ ((__nothrow__ , __leaf__)) ;
# 190 "/usr/include/stdio.h" 3 4
extern char *tempnam (const char *__dir, const char *__pfx)
     __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__malloc__)) ;
 
 
 
 
 
 
 
extern int fclose (FILE *__stream);
 
 
 
 
extern int fflush (FILE *__stream);
# 213 "/usr/include/stdio.h" 3 4
extern int fflush_unlocked (FILE *__stream);
# 232 "/usr/include/stdio.h" 3 4
extern FILE *fopen (const char *__restrict __filename,
      const char *__restrict __modes) ;
 
 
 
 
extern FILE *freopen (const char *__restrict __filename,
        const char *__restrict __modes,
        FILE *__restrict __stream) ;
# 265 "/usr/include/stdio.h" 3 4
extern FILE *fdopen (int __fd, const char *__modes) __attribute__ ((__nothrow__ , __leaf__)) ;
# 278 "/usr/include/stdio.h" 3 4
extern FILE *fmemopen (void *__s, size_t __len, const char *__modes)
  __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
 
 
extern FILE *open_memstream (char **__bufloc, size_t *__sizeloc) __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
 
 
 
extern void setbuf (FILE *__restrict __stream, char *__restrict __buf) __attribute__ ((__nothrow__ , __leaf__));
 
 
 
extern int setvbuf (FILE *__restrict __stream, char *__restrict __buf,
      int __modes, size_t __n) __attribute__ ((__nothrow__ , __leaf__));
 
 
 
 
extern void setbuffer (FILE *__restrict __stream, char *__restrict __buf,
         size_t __size) __attribute__ ((__nothrow__ , __leaf__));
 
 
extern void setlinebuf (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
 
 
 
 
 
 
 
extern int fprintf (FILE *__restrict __stream,
      const char *__restrict __format, ...);
 
 
 
 
extern int printf (const char *__restrict __format, ...);
 
extern int sprintf (char *__restrict __s,
      const char *__restrict __format, ...) __attribute__ ((__nothrow__));
 
 
 
 
 
extern int vfprintf (FILE *__restrict __s, const char *__restrict __format,
       __gnuc_va_list __arg);
 
 
 
 
extern int vprintf (const char *__restrict __format, __gnuc_va_list __arg);
 
extern int vsprintf (char *__restrict __s, const char *__restrict __format,
       __gnuc_va_list __arg) __attribute__ ((__nothrow__));
 
 
 
extern int snprintf (char *__restrict __s, size_t __maxlen,
       const char *__restrict __format, ...)
     __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 4)));
 
extern int vsnprintf (char *__restrict __s, size_t __maxlen,
        const char *__restrict __format, __gnuc_va_list __arg)
     __attribute__ ((__nothrow__)) __attribute__ ((__format__ (__printf__, 3, 0)));
# 365 "/usr/include/stdio.h" 3 4
extern int vdprintf (int __fd, const char *__restrict __fmt,
       __gnuc_va_list __arg)
     __attribute__ ((__format__ (__printf__, 2, 0)));
extern int dprintf (int __fd, const char *__restrict __fmt, ...)
     __attribute__ ((__format__ (__printf__, 2, 3)));
 
 
 
 
 
 
 
extern int fscanf (FILE *__restrict __stream,
     const char *__restrict __format, ...) ;
 
 
 
 
extern int scanf (const char *__restrict __format, ...) ;
 
extern int sscanf (const char *__restrict __s,
     const char *__restrict __format, ...) __attribute__ ((__nothrow__ , __leaf__));
# 395 "/usr/include/stdio.h" 3 4
extern int fscanf (FILE *__restrict __stream, const char *__restrict __format, ...) __asm__ ("" "__isoc99_fscanf")
 
                               ;
extern int scanf (const char *__restrict __format, ...) __asm__ ("" "__isoc99_scanf")
                              ;
extern int sscanf (const char *__restrict __s, const char *__restrict __format, ...) __asm__ ("" "__isoc99_sscanf") __attribute__ ((__nothrow__ , __leaf__))
 
                      ;
# 420 "/usr/include/stdio.h" 3 4
extern int vfscanf (FILE *__restrict __s, const char *__restrict __format,
      __gnuc_va_list __arg)
     __attribute__ ((__format__ (__scanf__, 2, 0))) ;
 
 
 
 
 
extern int vscanf (const char *__restrict __format, __gnuc_va_list __arg)
     __attribute__ ((__format__ (__scanf__, 1, 0))) ;
 
 
extern int vsscanf (const char *__restrict __s,
      const char *__restrict __format, __gnuc_va_list __arg)
     __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__format__ (__scanf__, 2, 0)));
# 443 "/usr/include/stdio.h" 3 4
extern int vfscanf (FILE *__restrict __s, const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vfscanf")
 
 
 
     __attribute__ ((__format__ (__scanf__, 2, 0))) ;
extern int vscanf (const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vscanf")
 
     __attribute__ ((__format__ (__scanf__, 1, 0))) ;
extern int vsscanf (const char *__restrict __s, const char *__restrict __format, __gnuc_va_list __arg) __asm__ ("" "__isoc99_vsscanf") __attribute__ ((__nothrow__ , __leaf__))
 
 
 
     __attribute__ ((__format__ (__scanf__, 2, 0)));
# 477 "/usr/include/stdio.h" 3 4
extern int fgetc (FILE *__stream);
extern int getc (FILE *__stream);
 
 
 
 
 
extern int getchar (void);
# 495 "/usr/include/stdio.h" 3 4
extern int getc_unlocked (FILE *__stream);
extern int getchar_unlocked (void);
# 506 "/usr/include/stdio.h" 3 4
extern int fgetc_unlocked (FILE *__stream);
# 517 "/usr/include/stdio.h" 3 4
extern int fputc (int __c, FILE *__stream);
extern int putc (int __c, FILE *__stream);
 
 
 
 
 
extern int putchar (int __c);
# 537 "/usr/include/stdio.h" 3 4
extern int fputc_unlocked (int __c, FILE *__stream);
 
 
 
 
 
 
 
extern int putc_unlocked (int __c, FILE *__stream);
extern int putchar_unlocked (int __c);
 
 
 
 
 
 
extern int getw (FILE *__stream);
 
 
extern int putw (int __w, FILE *__stream);
 
 
 
 
 
 
 
extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
     ;
# 603 "/usr/include/stdio.h" 3 4
extern __ssize_t __getdelim (char **__restrict __lineptr,
          size_t *__restrict __n, int __delimiter,
          FILE *__restrict __stream) ;
extern __ssize_t getdelim (char **__restrict __lineptr,
        size_t *__restrict __n, int __delimiter,
        FILE *__restrict __stream) ;
 
 
 
 
 
 
 
extern __ssize_t getline (char **__restrict __lineptr,
       size_t *__restrict __n,
       FILE *__restrict __stream) ;
 
 
 
 
 
 
 
extern int fputs (const char *__restrict __s, FILE *__restrict __stream);
 
 
 
 
 
extern int puts (const char *__s);
 
 
 
 
 
 
extern int ungetc (int __c, FILE *__stream);
 
 
 
 
 
 
extern size_t fread (void *__restrict __ptr, size_t __size,
       size_t __n, FILE *__restrict __stream) ;
 
 
 
 
extern size_t fwrite (const void *__restrict __ptr, size_t __size,
        size_t __n, FILE *__restrict __s);
# 673 "/usr/include/stdio.h" 3 4
extern size_t fread_unlocked (void *__restrict __ptr, size_t __size,
         size_t __n, FILE *__restrict __stream) ;
extern size_t fwrite_unlocked (const void *__restrict __ptr, size_t __size,
          size_t __n, FILE *__restrict __stream);
 
 
 
 
 
 
 
extern int fseek (FILE *__stream, long int __off, int __whence);
 
 
 
 
extern long int ftell (FILE *__stream) ;
 
 
 
 
extern void rewind (FILE *__stream);
# 707 "/usr/include/stdio.h" 3 4
extern int fseeko (FILE *__stream, __off_t __off, int __whence);
 
 
 
 
extern __off_t ftello (FILE *__stream) ;
# 731 "/usr/include/stdio.h" 3 4
extern int fgetpos (FILE *__restrict __stream, fpos_t *__restrict __pos);
 
 
 
 
extern int fsetpos (FILE *__stream, const fpos_t *__pos);
# 757 "/usr/include/stdio.h" 3 4
extern void clearerr (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
 
extern int feof (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
 
extern int ferror (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
 
extern void clearerr_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
extern int feof_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
extern int ferror_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
 
 
 
 
 
extern void perror (const char *__s);
 
 
 
 
 
# 1 "/usr/include/x86_64-linux-gnu/bits/sys_errlist.h" 1 3 4
# 26 "/usr/include/x86_64-linux-gnu/bits/sys_errlist.h" 3 4
extern int sys_nerr;
extern const char *const sys_errlist[];
# 782 "/usr/include/stdio.h" 2 3 4
 
 
 
 
extern int fileno (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
 
 
extern int fileno_unlocked (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
# 800 "/usr/include/stdio.h" 3 4
extern FILE *popen (const char *__command, const char *__modes) ;
 
 
 
 
 
extern int pclose (FILE *__stream);
 
 
 
 
 
extern char *ctermid (char *__s) __attribute__ ((__nothrow__ , __leaf__));
# 840 "/usr/include/stdio.h" 3 4
extern void flockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
 
 
 
extern int ftrylockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__)) ;
 
 
extern void funlockfile (FILE *__stream) __attribute__ ((__nothrow__ , __leaf__));
# 868 "/usr/include/stdio.h" 3 4
 
# 2 "HelloWorld.c" 2
 
# 2 "HelloWorld.c"
int main(int argc, char const *argv[])
{
    printf("hello world!\n");
    return 0;
}
 

• gcc HelloWorld.c -S -c -o HelloWorld.s 编译：包含预处理，将 C 程序转换成汇编程序。

点击查看HelloWorld.s

xyjk1002@sheldon:~/cosmos/lesson01/HelloWorld$ cat HelloWorld.s
        .file   "HelloWorld.c"
        .text
        .section        .rodata
.LC0:
        .string "hello world!"
        .text
        .globl  main
        .type   main, @function
main:
.LFB0:
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        subq    $16, %rsp
        movl    %edi, -4(%rbp)
        movq    %rsi, -16(%rbp)
        leaq    .LC0(%rip), %rdi
        call    puts@PLT
        movl    $0, %eax
        leave
        .cfi_def_cfa 7, 8
        ret
        .cfi_endproc
.LFE0:
        .size   main, .-main
        .ident  "GCC: (Debian 7.3.0-19) 7.3.0"
        .section        .note.GNU-stack,"",@progbits
 

• gcc HelloWorld.c -c -o HelloWorld.o 汇编：包含预处理和编译，将汇编程序转换成可链接的二进制程序

•gcc HelloWorld.c -o HelloWorld 链接：包含以上所有操作，将可链接的二进制程序和其它别的库链接在一起，形成可执行的程序文件。

程序装载执行

根据冯诺依曼体系结构构成的计算机，必须具有如下功能：

• 把程序和数据装入到计算机中；

• 必须具有长期记住程序、数据的中间结果及最终运算结果；

• 完成各种算术、逻辑运算和数据传送等数据加工处理；

• 根据需要控制程序走向，并能根据指令控制机器的各部件协调操作；

• 能够按照要求将处理的数据结果显示给用户。

为了完成上述的功能，计算机必须具备五大基本组成部件：

• 装载数据和程序的输入设备；

• 记住程序和数据的存储器；

• 完成数据加工处理的运算器；

• 控制程序执行的控制器；

• 显示处理结果的输出设备。

根据冯诺依曼的理论，我们只要把图灵机的几个部件换成电子设备，就可以变成一个最小核心的电子计算机，如下图：

更形象地将 HelloWorld 程序装入原型计算机

通过 gcc -c -S HelloWorld 只能得到汇编代码。使用 objdump -d HelloWorld 程序即可获取到二进制代码，其中有很多库代码（只需关注 main 函数相关的代码）

Hello World的二进制代码

HelloWorld：     文件格式 elf64-x86-64
 
 
Disassembly of section .init:
 
00000000000004e8 <_init>:
 4e8:   48 83 ec 08             sub    $0x8,%rsp
 4ec:   48 8b 05 f5 0a 20 00    mov    0x200af5(%rip),%rax        # 200fe8 <__gmon_start__>
 4f3:   48 85 c0                test   %rax,%rax
 4f6:   74 02                   je     4fa <_init+0x12>
 4f8:   ff d0                   callq  *%rax
 4fa:   48 83 c4 08             add    $0x8,%rsp
 4fe:   c3                      retq
 
Disassembly of section .plt:
 
0000000000000500 <.plt>:
 500:   ff 35 02 0b 20 00       pushq  0x200b02(%rip)        # 201008 <_GLOBAL_OFFSET_TABLE_+0x8>
 506:   ff 25 04 0b 20 00       jmpq   *0x200b04(%rip)        # 201010 <_GLOBAL_OFFSET_TABLE_+0x10>
 50c:   0f 1f 40 00             nopl   0x0(%rax)
 
0000000000000510 <puts@plt>:
 510:   ff 25 02 0b 20 00       jmpq   *0x200b02(%rip)        # 201018 <puts@GLIBC_2.2.5>
 516:   68 00 00 00 00          pushq  $0x0
 51b:   e9 e0 ff ff ff          jmpq   500 <.plt>
 
Disassembly of section .plt.got:
 
0000000000000520 <__cxa_finalize@plt>:
 520:   ff 25 d2 0a 20 00       jmpq   *0x200ad2(%rip)        # 200ff8 <__cxa_finalize@GLIBC_2.2.5>
 526:   66 90                   xchg   %ax,%ax
 
Disassembly of section .text:
 
0000000000000530 <_start>:
 530:   31 ed                   xor    %ebp,%ebp
 532:   49 89 d1                mov    %rdx,%r9
 535:   5e                      pop    %rsi
 536:   48 89 e2                mov    %rsp,%rdx
 539:   48 83 e4 f0             and    $0xfffffffffffffff0,%rsp
 53d:   50                      push   %rax
 53e:   54                      push   %rsp
 53f:   4c 8d 05 8a 01 00 00    lea    0x18a(%rip),%r8        # 6d0 <__libc_csu_fini>
 546:   48 8d 0d 13 01 00 00    lea    0x113(%rip),%rcx        # 660 <__libc_csu_init>
 54d:   48 8d 3d e6 00 00 00    lea    0xe6(%rip),%rdi        # 63a <main>
 554:   ff 15 86 0a 20 00       callq  *0x200a86(%rip)        # 200fe0 <__libc_start_main@GLIBC_2.2.5>
 55a:   f4                      hlt
 55b:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
 
0000000000000560 <deregister_tm_clones>:
 560:   48 8d 3d c9 0a 20 00    lea    0x200ac9(%rip),%rdi        # 201030 <__TMC_END__>
 567:   55                      push   %rbp
 568:   48 8d 05 c1 0a 20 00    lea    0x200ac1(%rip),%rax        # 201030 <__TMC_END__>
 56f:   48 39 f8                cmp    %rdi,%rax
 572:   48 89 e5                mov    %rsp,%rbp
 575:   74 19                   je     590 <deregister_tm_clones+0x30>
 577:   48 8b 05 5a 0a 20 00    mov    0x200a5a(%rip),%rax        # 200fd8 <_ITM_deregisterTMCloneTable>
 57e:   48 85 c0                test   %rax,%rax
 581:   74 0d                   je     590 <deregister_tm_clones+0x30>
 583:   5d                      pop    %rbp
 584:   ff e0                   jmpq   *%rax
 586:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
 58d:   00 00 00
 590:   5d                      pop    %rbp
 591:   c3                      retq
 592:   0f 1f 40 00             nopl   0x0(%rax)
 596:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
 59d:   00 00 00
 
00000000000005a0 <register_tm_clones>:
 5a0:   48 8d 3d 89 0a 20 00    lea    0x200a89(%rip),%rdi        # 201030 <__TMC_END__>
 5a7:   48 8d 35 82 0a 20 00    lea    0x200a82(%rip),%rsi        # 201030 <__TMC_END__>
 5ae:   55                      push   %rbp
 5af:   48 29 fe                sub    %rdi,%rsi
 5b2:   48 89 e5                mov    %rsp,%rbp
 5b5:   48 c1 fe 03             sar    $0x3,%rsi
 5b9:   48 89 f0                mov    %rsi,%rax
 5bc:   48 c1 e8 3f             shr    $0x3f,%rax
 5c0:   48 01 c6                add    %rax,%rsi
 5c3:   48 d1 fe                sar    %rsi
 5c6:   74 18                   je     5e0 <register_tm_clones+0x40>
 5c8:   48 8b 05 21 0a 20 00    mov    0x200a21(%rip),%rax        # 200ff0 <_ITM_registerTMCloneTable>
 5cf:   48 85 c0                test   %rax,%rax
 5d2:   74 0c                   je     5e0 <register_tm_clones+0x40>
 5d4:   5d                      pop    %rbp
 5d5:   ff e0                   jmpq   *%rax
 5d7:   66 0f 1f 84 00 00 00    nopw   0x0(%rax,%rax,1)
 5de:   00 00
 5e0:   5d                      pop    %rbp
 5e1:   c3                      retq
 5e2:   0f 1f 40 00             nopl   0x0(%rax)
 5e6:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
 5ed:   00 00 00
 
00000000000005f0 <__do_global_dtors_aux>:
 5f0:   80 3d 39 0a 20 00 00    cmpb   $0x0,0x200a39(%rip)        # 201030 <__TMC_END__>
 5f7:   75 2f                   jne    628 <__do_global_dtors_aux+0x38>
 5f9:   48 83 3d f7 09 20 00    cmpq   $0x0,0x2009f7(%rip)        # 200ff8 <__cxa_finalize@GLIBC_2.2.5>
 600:   00
 601:   55                      push   %rbp
 602:   48 89 e5                mov    %rsp,%rbp
 605:   74 0c                   je     613 <__do_global_dtors_aux+0x23>
 607:   48 8b 3d 1a 0a 20 00    mov    0x200a1a(%rip),%rdi        # 201028 <__dso_handle>
 60e:   e8 0d ff ff ff          callq  520 <__cxa_finalize@plt>
 613:   e8 48 ff ff ff          callq  560 <deregister_tm_clones>
 618:   c6 05 11 0a 20 00 01    movb   $0x1,0x200a11(%rip)        # 201030 <__TMC_END__>
 61f:   5d                      pop    %rbp
 620:   c3                      retq
 621:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)
 628:   f3 c3                   repz retq
 62a:   66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
 
0000000000000630 <frame_dummy>:
 630:   55                      push   %rbp
 631:   48 89 e5                mov    %rsp,%rbp
 634:   5d                      pop    %rbp
 635:   e9 66 ff ff ff          jmpq   5a0 <register_tm_clones>
 
000000000000063a <main>:
 63a:   55                      push   %rbp
 63b:   48 89 e5                mov    %rsp,%rbp
 63e:   48 83 ec 10             sub    $0x10,%rsp
 642:   89 7d fc                mov    %edi,-0x4(%rbp)
 645:   48 89 75 f0             mov    %rsi,-0x10(%rbp)
 649:   48 8d 3d 94 00 00 00    lea    0x94(%rip),%rdi        # 6e4 <_IO_stdin_used+0x4>
 650:   e8 bb fe ff ff          callq  510 <puts@plt>
 655:   b8 00 00 00 00          mov    $0x0,%eax
 65a:   c9                      leaveq
 65b:   c3                      retq
 65c:   0f 1f 40 00             nopl   0x0(%rax)
 
0000000000000660 <__libc_csu_init>:
 660:   41 57                   push   %r15
 662:   41 56                   push   %r14
 664:   49 89 d7                mov    %rdx,%r15
 667:   41 55                   push   %r13
 669:   41 54                   push   %r12
 66b:   4c 8d 25 76 07 20 00    lea    0x200776(%rip),%r12        # 200de8 <__frame_dummy_init_array_entry>
 672:   55                      push   %rbp
 673:   48 8d 2d 76 07 20 00    lea    0x200776(%rip),%rbp        # 200df0 <__init_array_end>
 67a:   53                      push   %rbx
 67b:   41 89 fd                mov    %edi,%r13d
 67e:   49 89 f6                mov    %rsi,%r14
 681:   4c 29 e5                sub    %r12,%rbp
 684:   48 83 ec 08             sub    $0x8,%rsp
 688:   48 c1 fd 03             sar    $0x3,%rbp
 68c:   e8 57 fe ff ff          callq  4e8 <_init>
 691:   48 85 ed                test   %rbp,%rbp
 694:   74 20                   je     6b6 <__libc_csu_init+0x56>
 696:   31 db                   xor    %ebx,%ebx
 698:   0f 1f 84 00 00 00 00    nopl   0x0(%rax,%rax,1)
 69f:   00
 6a0:   4c 89 fa                mov    %r15,%rdx
 6a3:   4c 89 f6                mov    %r14,%rsi
 6a6:   44 89 ef                mov    %r13d,%edi
 6a9:   41 ff 14 dc             callq  *(%r12,%rbx,8)
 6ad:   48 83 c3 01             add    $0x1,%rbx
 6b1:   48 39 dd                cmp    %rbx,%rbp
 6b4:   75 ea                   jne    6a0 <__libc_csu_init+0x40>
 6b6:   48 83 c4 08             add    $0x8,%rsp
 6ba:   5b                      pop    %rbx
 6bb:   5d                      pop    %rbp
 6bc:   41 5c                   pop    %r12
 6be:   41 5d                   pop    %r13
 6c0:   41 5e                   pop    %r14
 6c2:   41 5f                   pop    %r15
 6c4:   c3                      retq
 6c5:   90                      nop
 6c6:   66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
 6cd:   00 00 00
 
00000000000006d0 <__libc_csu_fini>:
 6d0:   f3 c3                   repz retq
 
Disassembly of section .fini:
 
00000000000006d4 <_fini>:
 6d4:   48 83 ec 08             sub    $0x8,%rsp
 6d8:   48 83 c4 08             add    $0x8,%rsp
 6dc:   c3                      retq
 

以上图中，分成四列：第一列为地址；第二列为十六进制，表示真正装入机器中的代码数据；第三列是对应的汇编代码；第四列是相关代码的注释。这是 x86_64 体系的代码，由此可以看出 x86 CPU 是变长指令集。

我们把这段代码数据装入最小电子计算机，状态如下图：

总结

现代电子计算机正是通过内存中的信息（指令和数据）做出相应的操作，并通过内存地址的变化，达到程序读取数据，控制程序流程（顺序、跳转对应该图灵机的读头来回移动）的功能。

思考题

为了实现 C 语言中函数的调用和返回功能，CPU 实现了函数调用和返回指令，即上图汇编代码中的“call”，“ret”指令，请你思考一下：call 和 ret 指令在逻辑上执行的操作是怎样的呢？

参考答案一：

1.call和ret指令都是转移指令，它们都修改IP的值，或同时修改CS和IP的值。它们经常共同用语实现子程序的设计。

2.CPU执行ret指令时，
（1）(IP)=((ss)*16+(sp))
得到IP地址，并将IP出栈
（2）(sp)=(sp)+2
将IP更新到 PC 寄存器中

3.CPU执行call指令时，进行两步操作：
(1)将当前的IP或CS和IP压入栈中；
(2)转移(jmp)到对应的ip或cs执行代码

注释：ss sp就是栈堆的指针,和cs ip 是代码段指针，知道ss，sp求物理地址的公式是 物理地址=ss* 16+ sp，或者物理地址=ss* 10H+ sp 也就是对于2进制来说，ss里的数要加上4个0 再加sp得到物理地址。比如ss存放 1234H sp 存放 2000H ，那么物理地址就是 1234H*10H+2000H=14340H

参考答案二：

首先假设CPU执行指令是顺序执行的，那么程序的调用需要考虑几个问题:
1，call指令要执行的代码在哪？也就是被调用函数的第一条指令所在的内存地址
2，被调用函数执行完之后，返回哪个位置继续执行？
只要解决上面这两个问题，那么函数调用时指令的间的跳转就迎刃而解了。

针对第一个问题，在gcc编译完成之后，函数对应的指令序列所在的位置就已经确定了，因此这是编译阶段需要考虑的问题

至于第二个问题，在执行完call指令的同时，需要将call指令下面一条指令的地址保存到栈内存中，同时更新%rsp寄存器指向的位置，然后就可以开始执行被调函数的指令序列，执行完毕后，由ret指令从rsp中获取栈顶的returnadress地址，然后跳转到call的下一条指令继续执行。

参考

极客时间-操作系统实战45讲