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<title>Boost.Build v2 user manual</title>
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<body>
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<p><a href="../../index.htm"><img class="banner" height="86" width="277"
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alt="C++ Boost" src="../../c++boost.gif"></a></p>
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<h1>Boost.Build v2 user manual<br class="clear">
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</h1>
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<hr>
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<div class="alert">
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This is preliminary version intended to document everything
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implemeneted but not yet ready for any practical use.
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</div>
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<br>
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<br>
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<hr>
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<dl class="page-index">
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<dt><a href="#sec-reference">Reference documentation</a></dt>
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<dd>
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<dl class="page-index">
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<dt><a href="#features_properties">Features and properties</a></dt>
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<dt><a href="#initialization">Initialization</a></dt>
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<dt><a href="#command_line">Command line</a></dt>
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<dt><a href="#projects">Projects</a></dt>
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<dt><a href="#targets">Targets</a></dt>
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<dt><a href="#build_process">Build process</a></dt>
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</dl>
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</dd>
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</dl>
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<hr>
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<h2><a name="sec-reference">Reference</a></h2>
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<h3><a name="features_properties">Features and properties</a></h3>
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<h4>Definition</h4>
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<p>A <em>feature</em> is a normalized (toolset-independent) description
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of an individual build parameter, such as whether inlining is
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enabled.</p>
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<p>A <em>property</em> is a (feature, value) pair. Each features is
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described by a name and the set of attributes from the following
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list:</p>
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<ul>
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<li>
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<em>incidental</em>
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<p>Incidental features do not affect build products at all. Warning
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level is one example. As a consequence, the build system doesn't try
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to avoid confusing targets with different values of incident
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properties.</p>
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<p>Features which are not incident are assumed to affect build
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products, therefore they are put in different directories as
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described in <a href="#target_paths">target paths</a> below.</p>
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</li>
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<li>
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<em>propagated</em>
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<p>Features of this kind are propagated to dependencies. That is, if
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a main target is build with a particular value of a propagated
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feature, and depends on some other main targets, the build systems
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attempts to use subvariants of those main targets with the same value
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of the feature.</p>
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</li>
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<li>
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<em>free-valued</em>
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<p>Usually, each feature takes takes a single value from a fixed set.
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In particular, this means that only one value can be used when
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building a single target. When a feature is free-valued, it can have
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several values at a time and each value can be an arbitrary string.
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For example, it is possible to have several preprocessor symbols
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defined simultaneously:</p>
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<pre>
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<define>NDEBUG=1 <define>HAS_CONFIG_H=1
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</pre>
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<br>
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<br>
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</li>
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<li>
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<em>optional</em>
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<p>An optional feature is not required to have a value during build.
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When a value of non-optional feature is not specified, it is always
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given the default value.</p>
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</li>
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<li>
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<em>symmetric</em>
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<p>A symmetric feature's default value, is not automatically included
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in <a href="#variants">build variants</a>. Normally a feature only
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generates a subvariant directory when its value differs from the
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value specified by the build variant, leading to an assymmetric
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subvariant directory structure for certain values of the feature. A
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symmetric feature, when relevant to the toolset, always generates a
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corresponding subvariant directory.</p>
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</li>
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<li>
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<em>path</em>
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<p>The value of path features specifies a path. The path is treated
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as relative to the directory of Jamfile where path feature is used
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and is translated appropriately by the build system when the build is
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invoked from a different directory</p>
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</li>
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<li>
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<em>implicit</em>
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<p>features whose values alone identify the feature. For example, a
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user is not required to write "<toolset>", but can simply write
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"gcc". Implicit feature names also don't appear in variant paths,
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although the values do. Thus: bin/gcc/... as opposed to
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bin/toolset-gcc/.... There should typically be only a few such
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features, to avoid possible name clashes.</p>
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</li>
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<li>
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<em>composite</em>
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<p>features which actually correspond to groups of properties. For
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example, a build variant is a composite feature. When generating
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targets from a set of build properties, composite features are
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recursively expanded and /added/ to the build property set, so rules
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can find them if neccessary. Non-composite non-free features override
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components of composite features in a build property set.</p>
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</li>
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<li>
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<em>link-incompatible</em>
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<p>See <a href="#link_compatibility">below</a>.</p>
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</li>
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<li>
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<em>executed</em>
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<div class="alert">
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Do we need it?
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</div>
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</li>
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<li>
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<em>dependency</em>
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<div class="alert">
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Do we need it?
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</div>
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</li>
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</ul>
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<p>TODO: give a name and describe the property set joined with slashes. I
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use the term "property path" somewhere below.</p>
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<h4 id="link_compatibility">Link compatible and imcompatible
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properties</h4>
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<p>It is possible that build system tries to generate a target with a
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certain set of properties but is is only possible to obtain a target with
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somewhat different property set. It is needed to know if the actual
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property set can be used instead of the property set that was needed. At
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this moment we use a simple approach to answering that question. Two
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property sets are called <em>link-compatible</em> when targets with those
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property sets can be used interchangably. In turn, two property sets are
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link compatible when there's no link-incompatible feature which has
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different values in those property sets.</p>
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<h4>Definition of property refinement</h4>
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<p>When a target with certain properties is requested, and that target
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requires some set of properties, it is needed to find the set of
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properties to use for building. This process is called <em>property
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refinement</em> and is performed by these rules</p>
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<ol>
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<li>If original properties and required properties are not
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link-compatible, refinement fails.</li>
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<li>Each property in the required set is added to the original property
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set</li>
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<li>If the original property set includes property with a different
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value of non free-valued feature, that property is removed.</li>
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</ol>
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<h3><a name="initialization">Initialization</a></h3>
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<p>Immediately upon startup, the <tt>bjam</tt> executable attempts to
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find the location of build system files. It does so by looking for a file
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called <tt>boost-build.jam</tt>. That file is first looked in the
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invocation directory and its parents up to the filesystem root, and then
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in the directories from variable BOOST_BUILD_PATH. When found, the file
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is loaded and should specify the build system location by calling the
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<tt>boost-build</tt> rule:</p>
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<pre>
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rule boost-build ( location ? )
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</pre>
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The directory specified by location and directories in
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<tt>BOOST_BUILD_PATH</tt> are searched for a file called
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<tt>bootstrap.jam</tt> which is loaded and completes startup.
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<p>This arrangement allows to make build system work without any
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environmental variables. For example, build system files can be placed in
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a directory <tt>boost-build</tt> at your project root, and a file
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<tt>boost-build.jam</tt> at the project root can contain:</p>
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<pre>
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boost-build boost-build ;
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</pre>
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In this case, running <tt>bjam</tt> in the project root will
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automatically find the build system.
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<h3><a name="command_line">Command line</a></h3>
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<p>Boost.Build extends Jam's command line in two ways. First, command
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line arguments can be used not only to specify targets to build, but also
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to specify build variants or arbitrary build request. Second, there are
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additional command line options.</p>
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<h4>Command line arguments</h4>
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Command line arguments specify targets and build request using the
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following rules.
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<ul>
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<li>An argument which does not contain slashes or the "=" symbol is
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either a value of an implicit feature, or target to be build. It is
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taken to be value of a feature if appropriate feature exists.
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Otherwise, it is considered target name.</li>
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<li>
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An argument with either slashes or the "=" symbol specifies build
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properties. It is converted into a set of build properties as
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follows:
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<ul>
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<li>The argument is split at each slash.</li>
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<li>
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Each component is converted into a set of properties. If
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component is a value of implicit feature, it is not changed.
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Otherwise, it should have the form
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<pre>
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<feature-name>=<feature-value>[","<feature-value>]*
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</pre>
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For each specified value, a propertry with that value and the
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specified feature name is added to the set.
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</li>
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<li>Property sets for each of the component are set-theoretically
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multiplicated.</li>
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</ul>
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</li>
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</ul>
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For example, the command line
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<pre>
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target1 debug gcc/runtime-link=dynamic,static
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</pre>
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would cause target called <tt>target1</tt> to be rebuild in debug mode,
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except that for gcc, both dynamically and statically linked binaries
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would be created.
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<p>TODO: should allow</p>
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<pre>
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target1 debug gcc,borland/runtime-link=static
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</pre>
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to work.
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<h4>Command line options</h4>
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<p>All of the Boost.Build options start with the "--" prefix. They are
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described in the following table.</p>
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<table align="center">
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<caption>
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Command line options
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</caption>
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<thead>
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<tr>
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<th>Option</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><tt>--debug</tt></td>
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<td>Enables internal checks.</td>
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</tr>
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<tr>
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<td><tt>--dump-projects</tt></td>
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<td>Cause the project structure to be output.</td>
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</tr>
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<tr>
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<td><tt>--help</tt></td>
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<td>Access to the online help system. This prints general
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information on how to use the help system with additional --help*
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options.</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="projects">Projects</a></h3>
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<p>Boost.Build considers every software it build as organized into
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projects, which corresponds to a single Jamfile. The project are
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organized in a hierarchical structure, so for each project we can talk
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about parent project, which is always unique and a number of subprojects.
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(TODO: project root).</p>
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<h4>Project attributes</h4>
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<p>For each project, there are several attributes.</p>
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<p><em>Project id</em> is used to denote the project from other project.
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Each project id is a hierarchical path, such as "boost/thread". When
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project-id need to be referred from other projects there are two
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alternatives:</p>
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<ul>
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<li>Use absolute proejct-id, which starts with "/", for example
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<tt>/boost/thread</tt>.</li>
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<li>Use relative project-id, which is appended to the project-id of the
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project where it is used.</li>
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</ul>
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<br>
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<br>
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<p><em>Source location</em> specifies directory where sources for the
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project are located.</p>
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<p><em>Project requirements</em> are requirements that apply to all the
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targets in the projects as well as all subprojects.</p>
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<p><em>Default build</em> is the build request that should be used when
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no build request is specified explicitly.</p>
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<p>The default values for those attributes are given in the table below.
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In order to affect them, Jamfile may call the <tt>project</tt> rule. The
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rule has this syntax:</p>
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<pre>
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project id : <attributes> ;
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</pre>
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Here, attributes is a sequence of (attribute-name, attribute-value)
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pairs. The list of attribute names along with its handling is shown in
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the table below. For example, it it possible to write:
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<pre>
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project tennis
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: requirements <threading>multi
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: default-build release
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;
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</pre>
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<table>
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<tr>
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<th>Attribute</th>
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<th>Name for the 'project' rule</th>
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<th>Default value</th>
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<th>Handling by the 'project' rule</th>
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</tr>
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<tr>
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<td>Project id</td>
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<td>none</td>
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<td>none</td>
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<td>Assigned from the first parameter of the 'project' rule. It is
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assumed to denote absolute project id.</td>
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</tr>
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<tr>
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<td>Source location</td>
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<td><tt>source-location</tt></td>
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<td>The location of jamfile for the project</td>
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<td>Sets to the passed value</td>
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</tr>
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<tr>
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<td>Requirements</td>
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<td><tt>requirements</tt></td>
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<td>The parent's requirements</td>
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<td>The parent's requirements are refined with the passed requirement
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and the result is used as the project requirements.</td>
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</tr>
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<tr>
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<td>Default build</td>
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<td><tt>default-build</tt></td>
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<td>TODO</td>
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<td>Sets to the passed value</td>
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</tr>
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</table>
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<h4>Project relationship</h4>
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<p>There are three kinds of project relationships.</p>
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<p>First is parent-child. This relationship is established implicitly:
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parent directories of a project are searched, and the first found Jamfile
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is assumed to define the parent project. The parent-child relationship
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affects only attribute values for the child project.</p>
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<p>Second is build relationship. Some project may request to recursively
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build other projects. Those project need not be child projects. The
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<tt>build-project</tt> rule is used for that:</p>
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<pre>
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build-project src ;
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</pre>
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<p>The third kind is the 'use' relationship. In means that one project
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uses targets from another. It is possible to just refer to target in
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other projects using target id. However, if target id uses project id, it
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is required that the project id is known. The <tt>use-project</tt> rule
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is employed to guarantee that.</p>
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<pre>
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use-project ( id : location )
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</pre>
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It loads the project at the specified location, which makes its project
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id available in the project which invokes the rule. It is required that
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the <tt>id</tt> parameter passed to the <tt>use-project</tt> rule be
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equal to the id that the loaded project declared. At this moment, the
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<tt>id</tt> paremeter should be absolute project id.
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<h3><a name="targets">Targets</a></h3>
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<h4>Main targets and main target alternatives</h4>
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<p><em>Main target</em> is a named entity which can be build, for example
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a named executable file. To declare a main target, user invokes some of
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the <a href="#main_target_rules">main target rules</a>, passing it things
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like list of source and requirement.</p>
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<p>It is possible to have different list of sources for different
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toolsets, therefore it is possible to invoce main target rules several
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times for a single main target. For example:</p>
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<pre>
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exe a.exe : a_gcc.cpp : <toolset> ;
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exe a.exe : a.cpp ;
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</pre>
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Each call to the 'exe' rule defines a new <em>main target
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alternative</em> for the main target <tt>a.exe</tt>. In this case, the
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first alternative will be used for the <tt>gcc</tt> toolset, while the
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second alternative will be used in other cases. TODO: document the exact
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selection method under "Build process" below.
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<h4>Target identifiers and references</h4>
|
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|
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<p>Target identifier is used to denote a target. It is described by the
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following grammar:</p>
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<pre>
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target-id -> project-reference local-target-name
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project-reference -> [jamfile-location] [ "@" [project-id] ]
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jamfile-location -> pathname
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project-id -> pathname
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local-target-name -> identifier
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</pre>
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For example, valid target ids might be:
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<pre>
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a
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lib/b
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@/boost/thread
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/home/ghost/build/lr_library@parser/lalr1
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</pre>
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To map the target id into target, the project where that target is
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contained is first found:
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<ol>
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<li>If <tt>project-reference</tt> is empty, then the current project is
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used — i.e. the project there the target id occurs.</li>
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|
|
<li>If the project id is absolute, the project with that id is
|
|
used.</li>
|
|
|
|
<li>If the project id is relative, it is treated relatively to
|
|
project-id of the project at <tt>jamfile-location</tt>. If that project
|
|
does not declare project id, it is an error.</li>
|
|
</ol>
|
|
After that, the target given by <tt>local-target-name</tt> in the found
|
|
project is used.
|
|
|
|
<p>Target reference is used to specify a source target, and may
|
|
additionally specify desired properties for that target. It has this
|
|
syntax:</p>
|
|
<pre>
|
|
target-reference -> target-id [ "/" requested-properties ]
|
|
requested-properties -> property-path
|
|
</pre>
|
|
For example,
|
|
<pre>
|
|
exe compiler : compiler.cpp libs/cmdline/<optimization>space ;
|
|
</pre>
|
|
would cause the version of <tt>cmdline</tt> library, optimized to space,
|
|
to be linked in even if the <tt>compile</tt> executable is build with
|
|
speed optimization.
|
|
|
|
<h5>Ambiguity resolution</h5>
|
|
|
|
<p>Target reference may have the same form as a pathname, for example
|
|
<tt>lib/a</tt>. In order to determine if this is target reference or
|
|
pathname, it is checked if there's a jamfile in the specified path. If
|
|
there is one, it is loaded and if the specified target is declared by
|
|
that project it is used. Otherwise, we just treat the target reference as
|
|
file name.</p>
|
|
|
|
<h4>Target paths</h4>
|
|
|
|
<p>To distinguish targets build with different properties, they are put
|
|
in different directories. Rules for determining target paths are given
|
|
below:</p>
|
|
|
|
<ol>
|
|
<li>All targets are placed under directory corresponding to the project
|
|
where they are defined.</li>
|
|
|
|
<li>Each non free-valued, non incident property cause an additional
|
|
element to be added to the target path. That element has the form
|
|
<tt><feature-name>-<feature-value></tt> for ordinary
|
|
features and <tt><feature-value></tt> for implicit ones. [Note
|
|
about composite features].</li>
|
|
|
|
<li>If the set of free-valued properties is different from the set of
|
|
free valued properties for the project to which the target belong, a
|
|
part of the form <tt>main_target-<name></tt> is added to the
|
|
target path. <b>Note:</b>It would be nice to track free-valued features
|
|
also, but this appears to be complex and not extremely needed.</li>
|
|
</ol>
|
|
|
|
<p>For example, we might have these paths:</p>
|
|
<pre>
|
|
debug/optimization-off
|
|
debug/main-target-a
|
|
|
|
</pre>
|
|
|
|
<h3><a name="build_process">Build process</a></h3>
|
|
|
|
<p>The build works in this way. On startup, the project in the current
|
|
directory is read. As the result a tree of projects is constructed. After
|
|
that, the build request is constructed from the command line. Then, the
|
|
steps are:</p>
|
|
|
|
<ol>
|
|
<li>The project in the current dir is passed the build request. If the
|
|
build request does not satisfy the project's requirements, a warning is
|
|
issued and the build of the project is skipped. Otherwise, the process
|
|
is repeated recusrively for all subprojects.</li>
|
|
|
|
<li>
|
|
An attempts to make all the main targets in the project is performed.
|
|
For each main target:
|
|
|
|
<ol>
|
|
<li>All main target alternatives which requirements are satisfied
|
|
by the build request are enumerated.</li>
|
|
|
|
<li>If there are several such alternatives, the one which longer
|
|
requirements list is selected.</li>
|
|
</ol>
|
|
</li>
|
|
|
|
<li>
|
|
For each selected alternative
|
|
|
|
<ol>
|
|
<li>Each target reference in the source list are recursively
|
|
constructed.</li>
|
|
|
|
<li>The dependency graph for the target is constructed by running
|
|
so called matching process, using generated source targets and
|
|
ordinary sources.</li>
|
|
</ol>
|
|
</li>
|
|
</ol>
|
|
|
|
<p>The dependency graph constructed for each target is build of so called
|
|
"virtual targets", which do not yet correspond to jam's targets. It is
|
|
therefore converted to jam's dependency graph which is then build.</p>
|
|
<hr>
|
|
|
|
<p class="revision">Last modified: Aug 5, 2002</p>
|
|
|
|
<p>© Copyright Vladimir Prus 2002. Permission to copy, use, modify,
|
|
sell and distribute this document is granted provided this copyright
|
|
notice appears in all copies. This document is provided ``as is'' without
|
|
express or implied warranty, and with no claim as to its suitability for
|
|
any purpose.</p>
|
|
</body>
|
|
</html>
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