FILE指针结构，glibc

最新推荐文章于 2021-04-30 00:29:33 发布

原创最新推荐文章于 2021-04-30 00:29:33 发布 · 273 阅读

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#FILE

本文探讨了glibc中FILE*指针被破坏导致segment fault的问题，通过gdbcore调试，展示了_IO_write_base等成员的错误指向，并提供了一段示例代码用于观察这些指针的变化。

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在glibc中，gdb core调试，显示FILE*指针内容（FILE写出现了core文件）

$1 = {_flags = 107276440, _IO_read_ptr = 0x3000000018 <Address 0x3000000018 out of bounds>, _IO_read_end = 0x2aea0006e9a0 "痍\006",

_IO_read_base = 0x2aea0006e8e0 "痍2045", _IO_write_base = 0x53305239 <Address 0x53305239 out of bounds>,

_IO_write_ptr = 0x35343032eaf0 <Address 0x35343032eaf0 out of bounds>, _IO_write_end = 0x2aea0006e9b0 "-", _IO_buf_base = 0x2aea0006e9f0 "[2014-03-24][23:41:45]",

_IO_buf_end = 0x2aea0006eaf0 "adfbc"..., _IO_save_base = 0x2 <Address 0x2 out of bounds>, _IO_backup_base = 0x2 <Address 0x2 out of bounds>,

_IO_save_end = 0x2aea000819c0 "\300\t\004", _markers = 0x0, _chain = 0x3, _fileno = 107625062, _flags2 = 56, _old_offset = 47184511166896, _cur_column = 59792,

_vtable_offset = 6 '\006', _shortbuf = "", _lock = 0x7fff599c0590, _offset = 5052268, __pad1 = 0x2aea0006e980, __pad2 = 0x2aea0006e9b0, __pad3 = 0x2aea0006ea18,

__pad4 = 0x2d26da68, __pad5 = 32, _mode = 453104, _unused2 = "\352*\000\000@\352\006\000\352*\000\000伴\006\000\352*\000"}

可以看到_IO_write_base 错误，因此该文件指针FILE已经被破坏。所以会出现segment fault错误。

通常_IO_write_base 与_IO_read_base都指向同一区域。

表示当前缓冲区的基地址。

0x2aea0006e9a0-0x2aea0006e8e0 = C0 = 192字节

下面这段程序打印地址：

#include <stdio.h>

#include <stdlib.h>

int main(int argc,char* argv[])

{

FILE *fp = fopen("test.txt","w");

char s[32]={0};