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192 lines
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>Using The LLVM Libraries</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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</head>
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<body>
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<div class="doc_title">Using The LLVM Libraries</div>
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<ol>
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<li><a href="#abstract">Abstract</a></li>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#descriptions">Library Descriptions</a></li>
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<li><a href="#rot">Linkage Rules Of Thumb</a>
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<ol>
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<li><a href="#always">Always link LLVMCore, LLVMSupport, LLVMSystem</a>
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<li><a href="#onlyone">Never link both archive and re-linked</a>
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</ol>
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</li>
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</ol>
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<div class="doc_author">
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<p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a></p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_section"><a name="abstract">Abstract</a></div>
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<div class="doc_text">
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<p>Amongst other things, LLVM is a toolkit for building compilers, linkers,
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runtime executives, virtual machines, and other program execution related
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tools. In addition to the LLVM tool set, the functionality of LLVM is
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available through a set of libraries. To use LLVM as a toolkit for
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constructing tools, a developer needs to understand what is contained in the
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various libraries, what they depend on, and how to use them. This document
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describes the contents of the libraries and how and when to use them.
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</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_section"> <a name="introduction">Introduction</a></div>
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<div class="doc_text">
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<p>If you're writing a compiler, virtual machine, or any other utility based
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on LLVM, you'll need to figure out which of the many libraries files you will
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need to link with to be successful. An understanding of the contents of these
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files and their inter-relationships will be useful in coming up with an optimal
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specification for the libraries to link with. The purpose of this document is
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to reduce some of the trial and error that the author experienced in using
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LLVM.</p>
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<p>LLVM produces two types of libraries: archives (ending in <tt>.a</tt>) and
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objects (ending in <tt>.o</tt>). However, both are libraries. Libraries ending
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in <tt>.o</tt> are known as re-linked libraries because they contain all the
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compilation units of the library linked together as a single <tt>.o</tt> file.
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Furthermore, many of the libraries have <em>both</em> forms of library. The
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re-linked libraries are used whenever you want to include all symbols from the
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library. The archive libraries are used whenever you want to only resolve
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outstanding symbols at that point in the link without including everything in
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the library. </p>
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<p>When linking your tools, you will use the <tt>LLVMLIBS</tt> make variable.
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(see the <a href="MakefileGuide.html#LLVMLIBS">Makefile Guide</a> for
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details). This variable specifies which LLVM libraries to link into your tool
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and the order in which they will be linked. You specify re-linked libraries by
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naming the library without a suffix. You specify archive libraries by naming
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the library with a <tt>.a</tt> suffix but without the <tt>lib</tt> prefix. The
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order in which the libraries appear in the <tt>LLVMLIBS</tt> variable
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definition is the order in which they will be linked. Getting this order
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correct for your tool can sometimes be challenging.
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</div>
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<!-- ======================================================================= -->
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<div class="doc_section"><a name="descriptions"></a>Library Descriptions</div>
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<div class="doc_text">
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<p>The table below categorizes each library
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<table style="text-align:left">
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<tr><th>Library</th><th>Forms</th><th>Description</th></tr>
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<tr><th colspan="3">Core Libraries</th></tr>
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<tr><td>LLVMAsmParser</td><td><tt>.o</tt></td>
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<td>LLVM Assembly Parsing</td></tr>
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<tr><td>LLVMBCReader</td><td><tt>.o</tt></td>
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<td>LLVM Bytecode Reading</td></tr>
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<tr><td>LLVMBCWriter</td><td><tt>.o</tt></td>
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<td>LLVM Bytecode Writing</td></tr>
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<tr><td>LLVMDebugger</td><td><tt>.o</tt></td>
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<td>Source Level Debugging Support</td></tr>
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<tr><td>LLVMSupport</td><td><tt>.a .o</tt></td>
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<td>General support utilities</td></tr>
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<tr><td>LLVMSystem</td><td><tt>.a .o</tt></td>
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<td>Operating system abstraction</td></tr>
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<tr><td>LLVMCore</td><td><tt>.o</tt></td>
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<td>LLVM Core IR</td></tr>
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<tr><th colspan="3">Analysis Libraries</th></tr>
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<tr><td>LLVMAnalysis</td><td><tt>.a .o</tt></td>
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<td>Various analysis passes.</td></tr>
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<tr><td>LLVMDataStructure</td><td><tt>.a .o</tt></td>
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<td>Data structure analysis passes.</td></tr>
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<tr><td>LLVMipa</td><td><tt>.a .o</tt></td>
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<td>Inter-procedural analysis passes.</td></tr>
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<tr><th colspan="3">Transformation Libraries</th></tr>
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<tr><td>LLVMInstrumentation</td><td><tt>.a .o</tt></td>
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<td>Instrumentation passes.</td></tr>
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<tr><td>LLVMipo</td><td><tt>.a .o</tt></td>
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<td>All inter-procedural optimization passes.</td></tr>
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<tr><td>LLVMScalarOpts</td><td><tt>.a .o</tt></td>
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<td>All scalar optimization passes.</td></tr>
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<tr><td>LLVMTransforms</td><td><tt>.a .o</tt></td>
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<td>Uncategorized transformation passes.</td></tr>
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<tr><td>LLVMTransformUtils</td><td><tt>.a .o</tt></td>
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<td>Transformation utilities.</td></tr>
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<tr><td>LLVMProfilePaths</td><td><tt>.o</tt></td>
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<td>Profile paths for instrumentation.</td></tr>
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<tr><th colspan="3">Code Generation Libraries </th></tr>
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<tr><td>LLVMCodeGen</td><td><tt>.o</tt></td>
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<td>Native code generation infrastructure</td></tr>
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<tr><th colspan="3">Target Libraries</th></tr>
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<tr><td>LLVMCBackend</td><td><tt>.o</tt></td>
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<td>'C' language code generator.</td></tr>
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<tr><td>LLVMPowerPC</td><td><tt>.o</tt></td>
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<td>PowerPC code generation backend</td></tr>
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<tr><td>LLVMSelectionDAG</td><td><tt>.o</tt></td>
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<td>Aggressive instruction selector for Directed Acyclic Graphs.</td></tr>
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<tr><td>LLVMSkeleton</td><td><tt>.a .o</tt></td>
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<td>Skeleton for a code generation backend.</td></tr>
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<tr><td>LLVMSparcV9</td><td><tt>.o</tt></td>
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<td>Code generation for SparcV9.</td></tr>
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<tr><td>LLVMSparcV9RegAlloc</td><td><tt>.a .o</tt></td>
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<td>Graph-coloring register allocator for SparcV9.</td></tr>
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<tr><td>LLVMSparcV9InstrSched</td><td><tt>.o</tt></td>
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<td>Instruction scheduling for SparcV9.</td></tr>
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<tr><td>LLVMSparcV9LiveVar</td><td><tt>.o</tt></td>
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<td>Live variable analysis SparcV9.</td></tr>
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<tr><td>LLVMSparcV9ModuloSched</td><td><tt>.o</tt></td>
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<td>Modulo scheduling for SparcV9.</td></tr>
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<tr><td>LLVMTarget</td><td><tt>.a .o</tt></td>
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<td>Generic code generation utilities.</td></tr>
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<tr><td>LLVMX86</td><td><tt>.o</tt></td>
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<td>Intel x86 code generation backend</td></tr>
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<tr><th colspan="3">Runtime Libraries</th></tr>
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<tr><td>LLVMInterpreter</td><td><tt>.o</tt></td>
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<td>Bytecode Interpreter</td></tr>
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<tr><td>LLVMJIT</td><td><tt>.o</tt></td>
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<td>Bytecode JIT Compiler</td></tr>
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<tr><td>LLVMExecutionEngine</td><td><tt>.o</tt></td>
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<td>Virtual machine engine</td></tr>
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<tr><td>LLVMexecve</td><td><tt>.o</tt></td>
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<td>execve(2) replacement for llee</td></tr>
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</table>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_section"><a name="rot">Linkage Rules Of Thumb</a></div>
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<div class="doc_text">
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<p>This section contains various "rules of thumb" about what files you
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should link into your programs.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection"><a name="always">Always Link LLVMCore, LLVMSupport,
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and LLVMSystem</a></div>
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<div class="doc_text">
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<p>No matter what you do with LLVM, the last three entries in the value of
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your LLVMLIBS make variable should always be:
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<tt>LLVMCore LLVMSupport.a LLVMSystem.a</tt>. There are no <tt>LLVM</tt>
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programs that don't depend on these three.</p>
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</div>
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<!-- ======================================================================= -->
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<div class="doc_subsection"><a name="onlyone">Never link both archive and
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re-linked library</a></div>
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<div class="doc_text">
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<p>There is never any point to linking both the re-linked (<tt>.o</tt>) and
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the archive (<tt>.a</tt>) versions of a library. Since the re-linked version
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includes the entire library, the archive version will not resolve any symbols.
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You could even end up with link error if you place the archive version before
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the re-linked version on the linker's command line.</p>
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</div>
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<!-- ======================================================================= -->
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<hr>
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<div class="doc_footer">
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<address>
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<a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
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</address>
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<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
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<br>Last modified: $Date$ </div>
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<!-- vim: sw=2 ts=2 ai
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-->
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