为系统调用设置catchpoint

例子

#include <stdio.h>

int main(void)
{
    char p1[] = "Sam";
    char *p2 = "Bob";

    printf("p1 is %s, p2 is %s\n", p1, p2);
    return 0;
}

技巧

使用gdb调试程序时，可以使用catch syscall [name | number]为关注的系统调用设置catchpoint，以上面程序为例：

(gdb) catch syscall mmap
Catchpoint 1 (syscall 'mmap' [9])
(gdb) r
Starting program: /home/nan/a

Catchpoint 1 (call to syscall mmap), 0x00000034e3a16f7a in mmap64 ()
   from /lib64/ld-linux-x86-64.so.2
(gdb) c
Continuing.

Catchpoint 1 (returned from syscall mmap), 0x00000034e3a16f7a in mmap64 ()
   from /lib64/ld-linux-x86-64.so.2

可以看到当mmap调用发生后，gdb会暂停程序的运行。
也可以使用系统调用的编号设置catchpoint，仍以上面程序为例：

(gdb) catch syscall 9
Catchpoint 1 (syscall 'mmap' [9])
(gdb) r
Starting program: /home/nan/a

Catchpoint 1 (call to syscall mmap), 0x00000034e3a16f7a in mmap64 ()
   from /lib64/ld-linux-x86-64.so.2
(gdb) c
Continuing.

Catchpoint 1 (returned from syscall mmap), 0x00000034e3a16f7a in mmap64 ()
   from /lib64/ld-linux-x86-64.so.2
(gdb) c
Continuing.

Catchpoint 1 (call to syscall mmap), 0x00000034e3a16f7a in mmap64 ()
   from /lib64/ld-linux-x86-64.so.2

可以看到和使用catch syscall mmap效果是一样的。（系统调用和编号的映射参考具体的xml文件，以我的系统为例，就是在/usr/local/share/gdb/syscalls文件夹下的amd64-linux.xml。）

如果不指定具体的系统调用，则会为所有的系统调用设置catchpoint，仍以上面程序为例：

(gdb) catch syscall
Catchpoint 1 (any syscall)
(gdb) r
Starting program: /home/nan/a

Catchpoint 1 (call to syscall brk), 0x00000034e3a1618a in brk ()
   from /lib64/ld-linux-x86-64.so.2
(gdb) c
Continuing.

Catchpoint 1 (returned from syscall brk), 0x00000034e3a1618a in brk ()
   from /lib64/ld-linux-x86-64.so.2
(gdb)
Continuing.

Catchpoint 1 (call to syscall mmap), 0x00000034e3a16f7a in mmap64 ()
   from /lib64/ld-linux-x86-64.so.2

参见gdb手册.

贡献者

nanxiao