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### 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.

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