段错误
所谓的段错误就是指访问的内存超出了系统所给这个程序的内存空间,通常这个值是由gd tr来保存的,他是一个48位的寄存器,其中的32位是保存由它指向的 gdt表,后13位保存 相应于gdt的下标,最后3位包括了程序是否在内存中以及程序的在cpu中的运行级别,指向 的gdt是由以64位为一个单位的表,在这张表中就保存着程序运行的代码段以及数据段的起 始地址以及与此相应的段限和页面交换还有程序运行级别还有内存粒度等等的信息。
英文简介
A segmentation fault (often shortened to segfault) is a particular error condi tion that can occur during the operation of computer software. In short, a seg mentation fault occurs when a program attempts to access a memory location tha t it is not allowed to access, or attempts to access a memory location in a wa y that is not allowed (e.g., attempts to write to a read-only location, or to overwrite part of the operating system). Systems based on processors like the Motorola 68000 tend to refer to these events as Address or Bus errors. Segmentation is one approach to memory management and protection in the operat ing system. It has been superseded by paging for most purposes, but much of th e terminology of segmentation is still used, "segmentation fault" being an exa mple. Some operating systems still have segmentation at some logical level alt hough paging is used as the main memory management policy. On Unix-like operating systems, a process that accesses invalid memory receive s the SIGSEGV signal. On Microsoft Windows, a process that accesses invalid me mory receives the STATUS_ACCESS_VIOLATION exception. 另外,这里有个基本上对照的中文解释,来自库扩展阅读1; Quote: 一旦一个程序发生了 越界访问, cpu就会产生相应的保护,于是segmentation fault就出现 了通过上面的解释,段 错误应该就是访问了不可访问的内存,这个 内存区要么是不存在的, 要么是受到系统保护的,还有可能是缺少文件或者文件损坏。寻找程序安装维修按列,段错误的常见形式
在编程中以下几类做法容易导致段错误,基本是是错误地使用 指针引起的 1)访问系统数据区,尤其是往 系统保护的 内存地址写 数据最常见就是给一个指针以0地址 2)内存越界(数组越界,变量类型不一致等) 访问到不属于你的内存区域解决方法我们在用C/ C++语言写程序的时侯, 内存管理的绝大部分工作都是需要我们来做的。实际上,内存管理是一个比较繁琐的工作,无论你多高明,经验多丰富,难 免会在此处犯些小错误,而通常这些错误又是那么的浅显而易于消除。但是手工“除虫”(debug),往往是效率低下且让人厌烦的,本文将就"段错误"这个 内存访问越界的错误谈谈如何快速定位这些"段错误"的语句。 下面将就以下的一个存在段错误的程序介绍几种调试方法:1 dummy_function (void) 2 { 3 unsigned char *ptr = 0x00; 4 *ptr = 0x00; 5 } 6 7 int main (void) 8 { 9 dummy_function (); 10 11 return 0; 12 } |
xiaosuo@gentux test $ ./a.out 段错误 |
xiaosuo@gentux test $ gcc -g -rdynamic d.c xiaosuo@gentux test $ gdb ./a.out GNU gdb 6.5 Copyright (C) 2006 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i686-pc-linux-gnu"...Using host libthread_db library "/lib/libthread (gdb) r Starting program: /home/xiaosuo/test/a.out Program received signal SIGSEGV, Segmentation fault. 0x08048524 in dummy_function () at d.c:4 4 *ptr = 0x00; (gdb) |