GDB/MI Development and Front Ends (Debugging with GDB)

27.4 GDB/MI Development and Front Ends

The application which takes the MI output and presents the state of the program being debugged to the user is called a front end.

Since GDB/MI is used by a variety of front ends to GDB, changes to the MI interface may break existing usage. This section describes how the protocol changes and how to request previous version of the protocol when it does.

Some changes in MI need not break a carefully designed front end, and for these the MI version will remain unchanged. The following is a list of changes that may occur within one level, so front ends should parse MI output in a way that can handle them:

New MI commands may be added.
New fields may be added to the output of any MI command.
The range of values for fields with specified values, e.g., in_scope (see -var-update) may be extended.

If the changes are likely to break front ends, the MI version level will be increased by one. The new versions of the MI protocol are not compatible with the old versions. Old versions of MI remain available, allowing front ends to keep using them until they are modified to use the latest MI version.

Since --interpreter=mi always points to the latest MI version, it is recommended that front ends request a specific version of MI when launching GDB (e.g. --interpreter=mi2) to make sure they get an interpreter with the MI version they expect.

The following table gives a summary of the the released versions of the MI interface: the version number, the version of GDB in which it first appeared and the breaking changes compared to the previous version.

MI version	GDB version	Breaking changes
1	5.1	None
2	6.0	The `-environment-pwd`, `-environment-directory` and `-environment-path` commands now returns values using the MI output syntax, rather than CLI output syntax. `-var-list-children`’s `children` result field is now a list, rather than a tuple. `-var-update`’s `changelist` result field is now a list, rather than a tuple.

The best way to avoid unexpected changes in MI that might break your front end is to make your project known to GDB developers and follow development on gdb@sourceware.org and gdb-patches@sourceware.org.