如何在二进制执行期间挂钩所有linux系统调用

我试图修改linux系统调用的默认行为.目前我正试图在实际调用它们之前挂钩并添加一个简单的print语句.我知道GCC链接器的标准’wrap’选项以及它如何用于挂钩包装器Link to GCC Linker options.这完全适用于open(),fstat(),fwrite()等(我实际上挂钩了libc包装器).

更新：

限制是并非所有系统调用都与此方法相关联.
为了说明这一点,让我们采用一个简单的静态编译二进制.当我们尝试添加包装器时,它们会受到我们在main()之后引入的调用的影响(请参阅下面显示的strace输出)

> strace ./sample 

execve("./sample",["./sample"],[/* 72 vars */]) = 0
uname({sys="Linux",node="kumar",...})   = 0
brk(0)                                  = 0x71f000
brk(0x7201c0)                           = 0x7201c0
arch_prctl(ARCH_SET_FS,0x71f880)       = 0
readlink("/proc/self/exe","/home/admin/sample"...,4096) = 41
brk(0x7411c0)                           = 0x7411c0
brk(0x742000)                           = 0x742000
access("/etc/ld.so.nohwcap",F_OK)      = -1 ENOENT (No such file or directory)
fstat(1,{st_mode=S_IFCHR|0620,st_rdev=makedev(136,4),...}) = 0
mmap(NULL,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS,-1,0) = 0x7fbcc54d1000
write(1,"Hello from the wrapped readlink "...,36Hello from the wrapped readlink :з
) = 36
readlink("/usr/bin/gnome-www-browser","/etc/alternatives/gnome-www-brow"...,255) = 35
write(1,36/etc/alternatives/gnome-www-browser
) = 36
exit_group(36)                          = ?
+++ exited with 36 +++

如果我们仔细地注意到二进制文件,则第一个“未拦截的”调用readlink()(系统调用89,即0x59)来自这些行 – 一些链接器相关的代码部分(即_dl_get_origin)为其功能执行readlink().这些隐式的系统调用(虽然存在于二进制代码中)永远不会被我们的“包装”方法所吸引.

  000000000051875c <_dl_get_origin>:
  51875c:       b8 59 00 00 00          mov    $0x59,%eax
  518761:       55                      push   %rbp
  518762:       53                      push   %rbx
  518763:       48 81 ec 00 10 00 00    sub    $0x1000,%rsp
  51876a:       48 89 e6                mov    %rsp,%rsi
  51876d:       0f 05                   syscall 

如何将包装思想扩展到readlink()等系统调用(包括所有被调用的隐式调用)？ 最佳答案 ld有一个包装选项,引用from manual：

–wrap symbol

Use a wrapper function for symbol. Any undefined reference to symbol will be resolved to __wrap_symbol. Any undefined reference to __real_symbol will be resolved to symbol. This can be used to provide a wrapper for a system function. The wrapper function should be called __wrap_symbol. If it wishes to call the system function,it should call __real_symbol.

它也适用于系统调用.这是readlink的一个例子：

#include 

$gcc test.c -o a -Wl,--wrap=readlink
$./a
Hello from the wrapped readlink :з
/etc/alternatives/gnome-www-browser

$gcc test.c -c -o a.o -Wl,--wrap=readlink
$nm a.o
0000000000000037 T main
                 U memset
                 U puts
                 U readlink
                 U __real_readlink
                 U __stack_chk_fail
0000000000000000 T __wrap_readlink

$cat test2.c
#include