how to specify custom gdb path to Adapter

Hi,
I use cdt-gdb-vscode in eclipse theia application in linux. it is ok when I debug c++ code by default gdb. debug config as follows
{
"name": "c++ test",
"types": "gdb",
"request": "launch",
"program": "my c++ a.out",
"cwd": "${workspaceFolder}"
}
now I want to use my custom gdb to debug some specific c++ code. I set miDebuggerPath in configuration, but it seems that debugger still use default gdb, not my custom gdb. I am not sure whether miDebuggerPath is the right param. config as follow
{
"name": "custom gdb c++ test",
"types": "gdb",
"request": "launch",
"program": "my c++ a.out",
"cwd": "${workspaceFolder}",
"MIMode": "gdb",
"miDebuggerPath": "path/to/my/custom gdb"
}