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<div class="section" id="llvmbuild-guide">
<h1>LLVMBuild Guide<a class="headerlink" href="#llvmbuild-guide" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><a class="reference internal" href="#introduction" id="id1">Introduction</a></li>
<li><a class="reference internal" href="#project-organization" id="id2">Project Organization</a></li>
<li><a class="reference internal" href="#build-integration" id="id3">Build Integration</a></li>
<li><a class="reference internal" href="#component-overview" id="id4">Component Overview</a></li>
<li><a class="reference internal" href="#llvmbuild-format-reference" id="id5">LLVMBuild Format Reference</a></li>
</ul>
</div>
<div class="section" id="introduction">
<h2><a class="toc-backref" href="#id1">Introduction</a><a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2>
<p>This document describes the <code class="docutils literal"><span class="pre">LLVMBuild</span></code> organization and files which
we use to describe parts of the LLVM ecosystem. For description of
specific LLVMBuild related tools, please see the command guide.</p>
<p>LLVM is designed to be a modular set of libraries which can be flexibly
mixed together in order to build a variety of tools, like compilers,
JITs, custom code generators, optimization passes, interpreters, and so
on. Related projects in the LLVM system like Clang and LLDB also tend to
follow this philosophy.</p>
<p>In order to support this usage style, LLVM has a fairly strict structure
as to how the source code and various components are organized. The
<code class="docutils literal"><span class="pre">LLVMBuild.txt</span></code> files are the explicit specification of that
structure, and are used by the build systems and other tools in order to
develop the LLVM project.</p>
</div>
<div class="section" id="project-organization">
<h2><a class="toc-backref" href="#id2">Project Organization</a><a class="headerlink" href="#project-organization" title="Permalink to this headline">¶</a></h2>
<p>The source code for LLVM projects using the LLVMBuild system (LLVM,
Clang, and LLDB) is organized into <em>components</em>, which define the
separate pieces of functionality that make up the project. These
projects may consist of many libraries, associated tools, build tools,
or other utility tools (for example, testing tools).</p>
<p>For the most part, the project contents are organized around defining
one main component per each subdirectory. Each such directory contains
an <code class="docutils literal"><span class="pre">LLVMBuild.txt</span></code> which contains the component definitions.</p>
<p>The component descriptions for the project as a whole are automatically
gathered by the LLVMBuild tools. The tools automatically traverse the
source directory structure to find all of the component description
files. NOTE: For performance/sanity reasons, we only traverse into
subdirectories when the parent itself contains an <code class="docutils literal"><span class="pre">LLVMBuild.txt</span></code>
description file.</p>
</div>
<div class="section" id="build-integration">
<h2><a class="toc-backref" href="#id3">Build Integration</a><a class="headerlink" href="#build-integration" title="Permalink to this headline">¶</a></h2>
<p>The LLVMBuild files themselves are just a declarative way to describe
the project structure. The actual building of the LLVM project is
handled by another build system (currently we support both
<a class="reference internal" href="MakefileGuide.html"><em>Makefiles</em></a> and <a class="reference internal" href="CMake.html"><em>CMake</em></a>).</p>
<p>The build system implementation will load the relevant contents of the
LLVMBuild files and use that to drive the actual project build.
Typically, the build system will only need to load this information at
“configure” time, and use it to generative native information. Build
systems will also handle automatically reconfiguring their information
when the contents of the <code class="docutils literal"><span class="pre">LLVMBuild.txt</span></code> files change.</p>
<p>Developers generally are not expected to need to be aware of the details
of how the LLVMBuild system is integrated into their build. Ideally,
LLVM developers who are not working on the build system would only ever
need to modify the contents of the <code class="docutils literal"><span class="pre">LLVMBuild.txt</span></code> description files
(although we have not reached this goal yet).</p>
<p>For more information on the utility tool we provide to help interfacing
with the build system, please see the <a class="reference internal" href="CommandGuide/llvm-build.html"><em>llvm-build</em></a> documentation.</p>
</div>
<div class="section" id="component-overview">
<h2><a class="toc-backref" href="#id4">Component Overview</a><a class="headerlink" href="#component-overview" title="Permalink to this headline">¶</a></h2>
<p>As mentioned earlier, LLVM projects are organized into logical
<em>components</em>. Every component is typically grouped into its own
subdirectory. Generally, a component is organized around a coherent
group of sources which have some kind of clear API separation from other
parts of the code.</p>
<p>LLVM primarily uses the following types of components:</p>
<ul class="simple">
<li><em>Libraries</em> - Library components define a distinct API which can be
independently linked into LLVM client applications. Libraries typically
have private and public header files, and may specify a link of required
libraries that they build on top of.</li>
<li><em>Build Tools</em> - Build tools are applications which are designed to be run
as part of the build process (typically to generate other source files).
Currently, LLVM uses one main build tool called <a class="reference internal" href="TableGen/index.html"><em>TableGen</em></a>
to generate a variety of source files.</li>
<li><em>Tools</em> - Command line applications which are built using the LLVM
component libraries. Most LLVM tools are small and are primarily
frontends to the library interfaces.</li>
</ul>
<p>Components are described using <code class="docutils literal"><span class="pre">LLVMBuild.txt</span></code> files in the directories
that define the component. See the <a class="reference internal" href="#llvmbuild-format-reference">LLVMBuild Format Reference</a> section
for information on the exact format of these files.</p>
</div>
<div class="section" id="llvmbuild-format-reference">
<h2><a class="toc-backref" href="#id5">LLVMBuild Format Reference</a><a class="headerlink" href="#llvmbuild-format-reference" title="Permalink to this headline">¶</a></h2>
<p>LLVMBuild files are written in a simple variant of the INI or configuration
file format (<a class="reference external" href="http://en.wikipedia.org/wiki/INI_file">Wikipedia entry</a>). The format defines a list of sections
each of which may contain some number of properties. A simple example of
the file format is below:</p>
<div class="highlight-ini"><div class="highlight"><pre><span class="c1">; Comments start with a semi-colon.</span>
<span class="c1">; Sections are declared using square brackets.</span>
<span class="k">[component_0]</span>
<span class="c1">; Properties are declared using '=' and are contained in the previous section.</span>
<span class="c1">;</span>
<span class="c1">; We support simple string and boolean scalar values and list values, where</span>
<span class="c1">; items are separated by spaces. There is no support for quoting, and so</span>
<span class="c1">; property values may not contain spaces.</span>
<span class="na">property_name</span> <span class="o">=</span> <span class="s">property_value</span>
<span class="na">list_property_name</span> <span class="o">=</span> <span class="s">value_1 value_2 ... value_n</span>
<span class="na">boolean_property_name</span> <span class="o">=</span> <span class="s">1 (or 0)</span>
</pre></div>
</div>
<p>LLVMBuild files are expected to define a strict set of sections and
properties. A typical component description file for a library
component would look like the following example:</p>
<div class="highlight-ini"><div class="highlight"><pre><span class="k">[component_0]</span>
<span class="na">type</span> <span class="o">=</span> <span class="s">Library</span>
<span class="na">name</span> <span class="o">=</span> <span class="s">Linker</span>
<span class="na">parent</span> <span class="o">=</span> <span class="s">Libraries</span>
<span class="na">required_libraries</span> <span class="o">=</span> <span class="s">Archive BitReader Core Support TransformUtils</span>
</pre></div>
</div>
<p>A full description of the exact sections and properties which are
allowed follows.</p>
<p>Each file may define exactly one common component, named <code class="docutils literal"><span class="pre">common</span></code>. The
common component may define the following properties:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">subdirectories</span></code> <strong>[optional]</strong></p>
<p>If given, a list of the names of the subdirectories from the current
subpath to search for additional LLVMBuild files.</p>
</li>
</ul>
<p>Each file may define multiple components. Each component is described by a
section who name starts with <code class="docutils literal"><span class="pre">component</span></code>. The remainder of the section
name is ignored, but each section name must be unique. Typically components
are just number in order for files with multiple components
(<code class="docutils literal"><span class="pre">component_0</span></code>, <code class="docutils literal"><span class="pre">component_1</span></code>, and so on).</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">Section names not matching this format (or the <code class="docutils literal"><span class="pre">common</span></code> section) are
currently unused and are disallowed.</p>
</div>
<p>Every component is defined by the properties in the section. The exact
list of properties that are allowed depends on the component type.
Components <strong>may not</strong> define any properties other than those expected
by the component type.</p>
<p>Every component must define the following properties:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span></code> <strong>[required]</strong></p>
<p>The type of the component. Supported component types are detailed
below. Most components will define additional properties which may be
required or optional.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">name</span></code> <strong>[required]</strong></p>
<p>The name of the component. Names are required to be unique across the
entire project.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">parent</span></code> <strong>[required]</strong></p>
<p>The name of the logical parent of the component. Components are
organized into a logical tree to make it easier to navigate and
organize groups of components. The parents have no semantics as far
as the project build is concerned, however. Typically, the parent
will be the main component of the parent directory.</p>
<p>Components may reference the root pseudo component using <code class="docutils literal"><span class="pre">$ROOT</span></code> to
indicate they should logically be grouped at the top-level.</p>
</li>
</ul>
<p>Components may define the following properties:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">dependencies</span></code> <strong>[optional]</strong></p>
<p>If specified, a list of names of components which <em>must</em> be built
prior to this one. This should only be exactly those components which
produce some tool or source code required for building the component.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last"><code class="docutils literal"><span class="pre">Group</span></code> and <code class="docutils literal"><span class="pre">LibraryGroup</span></code> components have no semantics for the
actual build, and are not allowed to specify dependencies.</p>
</div>
</li>
</ul>
<p>The following section lists the available component types, as well as
the properties which are associated with that component.</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span> <span class="pre">=</span> <span class="pre">Group</span></code></p>
<p>Group components exist purely to allow additional arbitrary structuring
of the logical components tree. For example, one might define a
<code class="docutils literal"><span class="pre">Libraries</span></code> group to hold all of the root library components.</p>
<p><code class="docutils literal"><span class="pre">Group</span></code> components have no additionally properties.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span> <span class="pre">=</span> <span class="pre">Library</span></code></p>
<p>Library components define an individual library which should be built
from the source code in the component directory.</p>
<p>Components with this type use the following properties:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">library_name</span></code> <strong>[optional]</strong></p>
<p>If given, the name to use for the actual library file on disk. If
not given, the name is derived from the component name itself.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">required_libraries</span></code> <strong>[optional]</strong></p>
<p>If given, a list of the names of <code class="docutils literal"><span class="pre">Library</span></code> or <code class="docutils literal"><span class="pre">LibraryGroup</span></code>
components which must also be linked in whenever this library is
used. That is, the link time dependencies for this component. When
tools are built, the build system will include the transitive closure
of all <code class="docutils literal"><span class="pre">required_libraries</span></code> for the components the tool needs.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">add_to_library_groups</span></code> <strong>[optional]</strong></p>
<p>If given, a list of the names of <code class="docutils literal"><span class="pre">LibraryGroup</span></code> components which
this component is also part of. This allows nesting groups of
components. For example, the <code class="docutils literal"><span class="pre">X86</span></code> target might define a library
group for all of the <code class="docutils literal"><span class="pre">X86</span></code> components. That library group might
then be included in the <code class="docutils literal"><span class="pre">all-targets</span></code> library group.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">installed</span></code> <strong>[optional]</strong> <strong>[boolean]</strong></p>
<p>Whether this library is installed. Libraries that are not installed
are only reported by <code class="docutils literal"><span class="pre">llvm-config</span></code> when it is run as part of a
development directory.</p>
</li>
</ul>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span> <span class="pre">=</span> <span class="pre">LibraryGroup</span></code></p>
<p><code class="docutils literal"><span class="pre">LibraryGroup</span></code> components are a mechanism to allow easy definition of
useful sets of related components. In particular, we use them to easily
specify things like “all targets”, or “all assembly printers”.</p>
<p>Components with this type use the following properties:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">required_libraries</span></code> <strong>[optional]</strong></p>
<p>See the <code class="docutils literal"><span class="pre">Library</span></code> type for a description of this property.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">add_to_library_groups</span></code> <strong>[optional]</strong></p>
<p>See the <code class="docutils literal"><span class="pre">Library</span></code> type for a description of this property.</p>
</li>
</ul>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span> <span class="pre">=</span> <span class="pre">TargetGroup</span></code></p>
<p><code class="docutils literal"><span class="pre">TargetGroup</span></code> components are an extension of <code class="docutils literal"><span class="pre">LibraryGroup</span></code>s,
specifically for defining LLVM targets (which are handled specially in a
few places).</p>
<p>The name of the component should always be the name of the target.</p>
<p>Components with this type use the <code class="docutils literal"><span class="pre">LibraryGroup</span></code> properties in
addition to:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">has_asmparser</span></code> <strong>[optional]</strong> <strong>[boolean]</strong></p>
<p>Whether this target defines an assembly parser.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">has_asmprinter</span></code> <strong>[optional]</strong> <strong>[boolean]</strong></p>
<p>Whether this target defines an assembly printer.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">has_disassembler</span></code> <strong>[optional]</strong> <strong>[boolean]</strong></p>
<p>Whether this target defines a disassembler.</p>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">has_jit</span></code> <strong>[optional]</strong> <strong>[boolean]</strong></p>
<p>Whether this target supports JIT compilation.</p>
</li>
</ul>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span> <span class="pre">=</span> <span class="pre">Tool</span></code></p>
<p><code class="docutils literal"><span class="pre">Tool</span></code> components define standalone command line tools which should be
built from the source code in the component directory and linked.</p>
<p>Components with this type use the following properties:</p>
<ul>
<li><p class="first"><code class="docutils literal"><span class="pre">required_libraries</span></code> <strong>[optional]</strong></p>
<p>If given, a list of the names of <code class="docutils literal"><span class="pre">Library</span></code> or <code class="docutils literal"><span class="pre">LibraryGroup</span></code>
components which this tool is required to be linked with.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The values should be the component names, which may not always
match up with the actual library names on disk.</p>
</div>
<p>Build systems are expected to properly include all of the libraries
required by the linked components (i.e., the transitive closure of
<code class="docutils literal"><span class="pre">required_libraries</span></code>).</p>
<p>Build systems are also expected to understand that those library
components must be built prior to linking – they do not also need
to be listed under <code class="docutils literal"><span class="pre">dependencies</span></code>.</p>
</li>
</ul>
</li>
<li><p class="first"><code class="docutils literal"><span class="pre">type</span> <span class="pre">=</span> <span class="pre">BuildTool</span></code></p>
<p><code class="docutils literal"><span class="pre">BuildTool</span></code> components are like <code class="docutils literal"><span class="pre">Tool</span></code> components, except that the
tool is supposed to be built for the platform where the build is running
(instead of that platform being targeted). Build systems are expected
to handle the fact that required libraries may need to be built for
multiple platforms in order to be able to link this tool.</p>
<p><code class="docutils literal"><span class="pre">BuildTool</span></code> components currently use the exact same properties as
<code class="docutils literal"><span class="pre">Tool</span></code> components, the type distinction is only used to differentiate
what the tool is built for.</p>
</li>
</ul>
</div>
</div>
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