為系統調用設置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調試程序時，可以使用catch syscall [name | number]為關注的系統調用設置catchpoint，以上面程序為例：

(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

可以看到當mmap調用發生後，gdb會暫停程序的運行。
也可以使用系統調用的編號設置catchpoint，仍以上面程序為例：

(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效果是一樣的。（系統調用和編號的映射參考具體的xml文件，以我的系統為例，就是在/usr/local/share/gdb/syscalls文件夾下的amd64-linux.xml。）

如果不指定具體的系統調用，則會為所有的系統調用設置catchpoint，仍以上面程序為例：

(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

參見gdb手冊.

貢獻者

nanxiao