GDB Internals

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GDB Internals

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4.2.1 Overview and Terminology

In general, execution of each GDB command produces some sort of output, and can even generate an input request.

Output can be generated for the following purposes:

to display a result of an operation;
to convey info or produce side-effects of a requested operation;
to provide a notification of an asynchronous event (including progress indication of a prolonged asynchronous operation);
to display error messages (including warnings);
to show debug data;
to query or prompt a user for input (a special case).

This section mainly concentrates on how to build result output, although some of it also applies to other kinds of output.

Generation of output that displays the results of an operation involves one or more of the following:

output of the actual data
formatting the output as appropriate for console output, to make it easily readable by humans
machine oriented formatting--a more terse formatting to allow for easy parsing by programs which read GDB's output
annotation, whose purpose is to help legacy GUIs to identify interesting parts in the output

The ui_out routines take care of the first three aspects. Annotations are provided by separate annotation routines. Note that use of annotations for an interface between a GUI and GDB is deprecated.

Output can be in the form of a single item, which we call a field; a list consisting of identical fields; a tuple consisting of non-identical fields; or a table, which is a tuple consisting of a header and a body. In a BNF-like form:

<table> ==>: <header> <body>
<header> ==>: { <column> }
<column> ==>: <width> <alignment> <title>
<body> ==>: {<row>}