### 27.23 gdb/mi Support Commands

Since new commands and features get regularly added to gdb/mi, some commands are available to help front-ends query the debugger about support for these capabilities. Similarly, it is also possible to query gdb about target support of certain features.

#### The `-info-gdb-mi-command` Command

##### Synopsis

          -info-gdb-mi-command cmd_name

Query support for the gdb/mi command named cmd_name.

Note that the dash (`-`) starting all gdb/mi commands is technically not part of the command name (see GDB/MI Input Syntax), and thus should be omitted in cmd_name. However, for ease of use, this command also accepts the form with the leading dash.

##### gdb Command

There is no corresponding gdb command.

##### Result

The result is a tuple. There is currently only one field:

``exists`'
  This field is equal to `"true"` if the gdb/mi command exists, `"false"` otherwise.

##### Example

Here is an example where the gdb/mi command does not exist:

         -info-gdb-mi-command unsupported-command
         ^done,command={exists="false"}

And here is an example where the gdb/mi command is known to the debugger:

         -info-gdb-mi-command symbol-list-lines
         ^done,command={exists="true"}

#### The `-list-features` Command

Returns a list of particular features of the MI protocol that this version of gdb implements. A feature can be a command, or a new field in an output of some command, or even an important bugfix. While a frontend can sometimes detect presence of a feature at runtime, it is easier to perform detection at debugger startup.

The command returns a list of strings, with each string naming an available feature. Each returned string is just a name, it does not have any internal structure. The list of possible feature names is given below.

Example output:

         (gdb) -list-features
         ^done,result=["feature1","feature2"]

The current list of features is:

``frozen-varobjs`'
  Indicates support for the `-var-set-frozen` command, as well as possible presense of the `frozen` field in the output of `-varobj-create`.
``pending-breakpoints`'
  Indicates support for the `-f` option to the `-break-insert` command.
``python`'
  Indicates Python scripting support, Python-based pretty-printing commands, and possible presence of the ``display_hint`' field in the output of `-var-list-children`
``thread-info`'
  Indicates support for the `-thread-info` command.
``data-read-memory-bytes`'
  Indicates support for the `-data-read-memory-bytes` and the `-data-write-memory-bytes` commands.
``breakpoint-notifications`'
  Indicates that changes to breakpoints and breakpoints created via the CLI will be announced via async records.
``ada-task-info`'
  Indicates support for the `-ada-task-info` command.
``language-option`'
  Indicates that all gdb/mi commands accept the `--language` option (see Context management).
``info-gdb-mi-command`'
  Indicates support for the `-info-gdb-mi-command` command.
``undefined-command-error-code`'
  Indicates support for the "undefined-command" error code in error result records, produced when trying to execute an undefined gdb/mi command (see GDB/MI Result Records).
``exec-run-start-option`'
  Indicates that the `-exec-run` command supports the `--start` option (see GDB/MI Program Execution).

#### The `-list-target-features` Command

Returns a list of particular features that are supported by the target. Those features affect the permitted MI commands, but unlike the features reported by the `-list-features` command, the features depend on which target GDB is using at the moment. Whenever a target can change, due to commands such as `-target-select`, `-target-attach` or `-exec-run`, the list of target features may change, and the frontend should obtain it again. Example output:

         (gdb) -list-target-features
         ^done,result=["async"]

The current list of features is:

``async`'
  Indicates that the target is capable of asynchronous command execution, which means that gdb will accept further commands while the target is running.
``reverse`'
  Indicates that the target is capable of reverse execution. See Reverse Execution, for more information.