Linux程序地址

news/2024/5/6 15:02:33/文章来源:https://blog.csdn.net/m0_63783532/article/details/133897237

一、定义

二、问题引出

三、虚拟地址和物理地址

（一）问题解释

（二）什么是进程地址空间

（三）为什么要有进程地址空间

一、定义

#include <stdio.h>    
#include <stdlib.h>//getenv的头文件    int un_gval;    
int init_gval=2;    
int main()    
{    printf("代码地址        ：%p\n", main);    const char *str = "hello world";    printf("常量地址        ：%p\n", str);    printf("已初始化数据地址：%p\n", &init_gval);    printf("未初始化数据地址：%p\n", &un_gval);                                                                                                  char *heap = (char*)malloc(100);    printf("堆区地址        ：%p\n", heap);    printf("栈区地址        ：%p\n", &str);    return 0;
}

#include <stdio.h>    
#include <stdlib.h>//getenv的头文件        
int main()    
{    const char *str="hello world";    char *heap1 = (char*)malloc(100);    char *heap2 = (char*)malloc(100);    char *heap3 = (char*)malloc(100);    char *heap4 = (char*)malloc(100);    printf("heap1 address：%p\n", heap1);                                                                                                        printf("heap2 address：%p\n", heap2);    printf("heap3 address：%p\n", heap3);    printf("heap4 address：%p\n", heap4);    printf("Stack1 address: %p\n", &str);    printf("Stack2 address: %p\n", &heap1);//变量heap1是在main函数内部定义    printf("Stack3 address: %p\n", &heap2);    printf("Stack4 address: %p\n", &heap3);    return 0;    
}

栈整体向下增长，但是一旦全部开辟好以后，局部向上使用
（例如一个数组int a[10] ，&a[0]<&a[9]）

二、问题引出

fork以后的父子进程，输出地址是一致的，但是变量内容不一样

  #include<stdio.h>#include<unistd.h>int g_val = 100;int main(){pid_t id = fork();if(id < 0){perror("fork");return 0;}else if(id == 0)//子进程{int cnt = 5;while(1){printf("child , pid: %d, ppid: %d, g_val: %d, &g_val: %p\n", getpid(),getppid(),g_val,&g_val);sleep(1);if(cnt == 0){g_val = 200;printf("child change g_val: 100->200\n");}                                                                                                      cnt--;}}else{//父进程while(1){printf("father, pid: %d, ppid: %d, g_val: %d, &g_val: %p\n",getpid(),getppid(),g_val,&g_val);sleep(1);}}return 0;}

三、虚拟地址和物理地址

（一）问题解释

每一个进程运行之后，都会有一个进程地址空间的存在（在系统层面都要有自己的页表映射结构）

（二）什么是进程地址空间

进程地址空间本质上是内存中的一种内核数据结构
在Linux当中进程地址空间具体由结构体mm_struct实现
进程地址空间是一个虚拟的内存空间，可以看做是一条从 0x00000000 到 0xffffffff 的线，这条线上被划分成不同的区域。
每个区域在进程地址空间中都有一定范围的地址划分。在实际运行中，这些虚拟地址会被操作系统内核映射到实际的物理内存地址上

struct mm_struct {struct vm_area_struct * mmap;		/* list of VMAs */struct rb_root mm_rb;struct vm_area_struct * mmap_cache;	/* last find_vma result */unsigned long (*get_unmapped_area) (struct file *filp,unsigned long addr, unsigned long len,unsigned long pgoff, unsigned long flags);void (*unmap_area) (struct vm_area_struct *area);unsigned long mmap_base;		/* base of mmap area */unsigned long free_area_cache;		/* first hole */pgd_t * pgd;atomic_t mm_users;			/* How many users with user space? */atomic_t mm_count;			/* How many references to "struct mm_struct" (users count as 1) */int map_count;				/* number of VMAs */struct rw_semaphore mmap_sem;spinlock_t page_table_lock;		/* Protects page tables, mm->rss, mm->anon_rss */struct list_head mmlist;		/* List of maybe swapped mm's.  These are globally strung* together off init_mm.mmlist, and are protected* by mmlist_lock*/unsigned long start_code, end_code, start_data, end_data;unsigned long start_brk, brk, start_stack;unsigned long arg_start, arg_end, env_start, env_end;unsigned long rss, anon_rss, total_vm, locked_vm, shared_vm;unsigned long exec_vm, stack_vm, reserved_vm, def_flags, nr_ptes;unsigned long saved_auxv[42]; /* for /proc/PID/auxv */unsigned dumpable:1;cpumask_t cpu_vm_mask;/* Architecture-specific MM context */mm_context_t context;/* Token based thrashing protection. */unsigned long swap_token_time;char recent_pagein;/* coredumping support */int core_waiters;struct completion *core_startup_done, core_done;/* aio bits */rwlock_t		ioctx_list_lock;struct kioctx		*ioctx_list;struct kioctx		default_kioctx;unsigned long hiwater_rss;	/* High-water RSS usage */unsigned long hiwater_vm;	/* High-water virtual memory usage */
};

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