gdb - GDB：以编程方式删除观察点

Question

是否可以在不知道观察点编号的情况下删除观察点？

我正在使用附加到断点的命令在内存位置设置观察点。我想在另一个断点清除观察点，但我不知道如何在没有观察点编号的情况下清除观察点。是否有可以通过内存位置删除观察点的命令？

Answer 1

最简单的方法是使用 $bpnum 便利变量，您可能希望将其存储在另一个便利变量中，以便以后创建断点/观察点时它不会改变。

(gdb) watch y
(gdb) set $foo_bp=$bpnum
Hardware watchpoint 2: y
(gdb) p $foo_bp
$1 = 2
(gdb) delete $foo_bp

Answer 2

保存观察点编号然后使用该编号删除观察点怎么样？

这是一个例子。我有一个 C++ 程序。当第 5 行的断点被命中时，我设置了三个观察点。对于观察点 #2，我保存了一个 gdb 命令文件，以便稍后将其删除。当 9 上的断点被命中时，我只执行这个 gdb 命令文件：

这是 main.cpp：

#include <stdio.h>
int main()
{
  int v3=2, v2=1, v1 =0 ;
  printf("Set a watchpoint\n");

  v1 = 1;
  v1 = 2;
  printf("Clear the watchpoint\n");

  v1 = 3;
  v1 = 4;

  return 0;
}

这是.gdbinit：

file ./a.out
b 5
commands
watch v2
watch v1
set pagination off
shell rm -f all_watchpoints
set logging file all_watchpoints
set logging on
info watchpoints
set logging off
shell rm -f delete_my_watchpoint
shell tail -n 1 all_watchpoints | awk ' {print "delete "$1 }' > delete_my_watchpoint
watch v3
echo Done\n
c
end
b 9
commands
source delete_my_watchpoint
info watchpoints
end
r

这只是 .gdbinit 的一个略微更改的版本，它不是使用删除观察点的命令保存文件，而是保存观察点编号：

file ./a.out
b 5
commands
watch v2
watch v1
set pagination off
shell rm -f all_watchpoints
set logging file all_watchpoints
set logging on
info watchpoints
set logging off
shell rm -f delete_my_watchpoint
shell tail -n 1 all_watchpoints | awk ' {print "set $watchpoint_to_delete_later="$1 }' > save_my_watchpoint_number
source save_my_watchpoint_number
shell rm -f save_my_watchpoint_number
shell rm -f all_watchpoints
watch v3
echo Done\n
c
end
b 9
commands
delete $watchpoint_to_delete_later
info watchpoints
end
r

如果您以这种方式使用地址设置观察点：

(gdb) watch *((int*)0x22ff44)
Hardware watchpoint 3: *((int*)0x22ff44)
(gdb) info watchpoints
Num     Type           Disp Enb Address    What
3       hw watchpoint  keep y              *((int*)0x22ff44)  

您也可以稍后找到此地址，因为它显示在info watchpoints

(gdb) set logging file all_watchpoints
(gdb) set logging on
Copying output to all_watchpoints.
(gdb) info watchpoints
Num     Type           Disp Enb Address    What
3       hw watchpoint  keep y              *((int*)0x22ff44)
4       hw watchpoint  keep y              *((int*)0x22ff48)
5       hw watchpoint  keep y              *((int*)0x22ff4B)
(gdb) set logging of
Done logging to all_watchpoints.
(gdb) shell grep 0x22ff48 all_watchpoints
4       hw watchpoint  keep y              *((int*)0x22ff48)
(gdb) shell grep 0x22ff48 all_watchpoints | awk ' {print $1}'
4
(gdb) shell grep 0x22ff48 all_watchpoints | awk ' {print "delete "$1}' > delete_watchpoint
(gdb) source delete_watchpoint
(gdb) info watchpoints
Num     Type           Disp Enb Address    What
3       hw watchpoint  keep y              *((int*)0x22ff44)
5       hw watchpoint  keep y              *((int*)0x22ff4B)