# 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`調用發生后，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](https://sourceware.org/gdb/onlinedocs/gdb/Set-Catchpoints.html). ## 貢獻者 nanxiao