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
本文来自博客园，作者：miyan，转载请注明原文链接：https://www.cnblogs.com/xyjk1002-rejuvenation/p/16626613.html
