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- Reorganized the document contents
- Provided a "General Layout" section that currently covers just the block structure of the bytecode file. - Wrote the section on the Global Type Pool - Wrote the section on differences between LLVM file format versions. Only five sections left to write! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14628 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer
parent
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@ -4,24 +4,31 @@
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<head>
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<title>LLVM Bytecode File Format</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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<style type="css">
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table, tr, td { border: 2px solid gray }
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th { border: 2px solid gray; font-weight: bold; }
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||||
table { border-collapse: collapse; margin-top: 1em margin-bottom: 1em }
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||||
<style type="text/css">
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||||
TR, TD { border: 2px solid gray; padding: 4pt 4pt 4pt 4pt; }
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||||
TH { border: 2px solid gray; font-weight: bold; font-size: 105%; }
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||||
TABLE { text-align: center; padding: 4pt 4pt 4pt 4pt; border: 2px solid black;
|
||||
border-collapse: collapse; margin-top: 1em; margin-left: 1em; margin-right: 1em; margin-bottom: 1em; }
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.td_left { border: 2px solid gray; padding: 4pt 4pt 4pt 4pt; text-align: left; }
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</style>
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</head>
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<body>
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<div class="doc_title"> LLVM Bytecode File Format </div>
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<ol>
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<li><a href="#abstract">Abstract</a></li>
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<li><a href="#general">General Concepts</a>
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<li><a href="#concepts">Concepts</a>
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||||
<ol>
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<li><a href="#blocks">Blocks</a></li>
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<li><a href="#lists">Lists</a></li>
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<li><a href="#fields">Fields</a></li>
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<li><a href="#slots">Slots</a></li>
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<li><a href="#encoding">Encoding Rules</a></li>
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<li><a href="#align">Alignment</a></li>
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<li><a href="#encoding">Encoding Primitives</a></li>
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<li><a href="#slots">Slots</a></li>
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</ol>
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</li>
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<li><a href="#general">General Layout</a>
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<ol>
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<li><a href="#structure">Structure</a></li>
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</ol>
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</li>
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<li><a href="#details">Detailed Layout</a>
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@ -30,11 +37,13 @@
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<li><a href="#blocktypes">Blocks Types</a></li>
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<li><a href="#signature">Signature Block</a></li>
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<li><a href="#module">Module Block</a></li>
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<li><a href="#typeool">Global Type Pool</a></li>
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<li><a href="#modinfo">Module Info Block</a></li>
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<li><a href="#constants">Global Constant Pool</a></li>
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<li><a href="#functions">Function Blocks</a></li>
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<li><a href="#symtab">Module Symbol Table</a></li>
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<li><a href="#globaltypes">Global Type Pool</a></li>
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<li><a href="#globalinfo">Module Info Block</a></li>
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<li><a href="#constantpool">Global Constant Pool</a></li>
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<li><a href="#functiondefs">Function Definition</a></li>
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<li><a href="#compactiontable">Compaction Table</a></li>
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<li><a href="#instructionlist">Instruction List</a></li>
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<li><a href="#symtab">Symbol Table</a></li>
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</ol>
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</li>
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<li><a href="#versiondiffs">Version Differences</a>
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@ -52,19 +61,21 @@
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<div class="doc_warning">
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<p>Warning: This is a work in progress.</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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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This document describes the LLVM bytecode
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file format. It specifies the binary encoding rules of the bytecode file format
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<p>This document describes the LLVM bytecode file format as of version 1.3.
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It specifies the binary encoding rules of the bytecode file format
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so that equivalent systems can encode bytecode files correctly. The LLVM
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bytecode representation is used to store the intermediate representation on
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disk in compacted form.
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</p>
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</div>
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<!-- *********************************************************************** -->
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<div class="doc_section"> <a name="general">General Concepts</a> </div>
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<div class="doc_section"> <a name="concepts">Concepts</a> </div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This section describes the general concepts of the bytecode file format
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@ -73,48 +84,42 @@ format may change in the future, but will always be backwards compatible with
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older formats. This document only describes the most current version of the
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bytecode format.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="blocks">Blocks</a> </div>
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<div class="doc_text">
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<p>LLVM bytecode files consist simply of a sequence of blocks of bytes.
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Each block begins with an identification value that determines the type of
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the next block. The possible types of blocks are described below in the section
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<a href="#blocktypes">Block Types</a>. The block identifier is used because
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it is possible for entire blocks to be omitted from the file if they are
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empty. The block identifier helps the reader determine which kind of block is
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next in the file.</p>
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<p>The following block identifiers are currently in use
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(from llvm/Bytecode/Format.h):</p>
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<ol>
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<li><b>Module (0x01)</b>.</li>
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<li><b>Function (0x11)</b>.</li>
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<li><b>ConstantPool (0x12)</b>.</li>
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<li><b>SymbolTable (0x13)</b>.</li>
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<li><b>ModuleGlobalInfo (0x14)</b>.</li>
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<li><b>GlobalTypePlane (0x15)</b>.</li>
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<li><b>BasicBlock (0x31)</b>.</li>
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<li><b>InstructionList (0x32)</b>.</li>
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<li><b>CompactionTable (0x33)</b>.</li>
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</ol>
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Each block begins with an header of two unsigned integers. The first value
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identifies the type of block and the second value provides the size of the
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block in bytes. The block identifier is used because it is possible for entire
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blocks to be omitted from the file if they are empty. The block identifier helps
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the reader determine which kind of block is next in the file. Note that blocks
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can be nested within other blocks.</p>
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<p> All blocks are variable length, and the block header specifies the size of
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the block. All blocks are rounded aligned to even 32-bit boundaries, so they
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always start and end of this boundary. Each block begins with an integer
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identifier and the length of the block, which does not include the padding
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bytes needed for alignment.</p>
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the block. All blocks begin on a byte index that is aligned to an even 32-bit
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boundary. That is, the first block is 32-bit aligned because it starts at offset
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0. Each block is padded with zero fill bytes to ensure that the next block also
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starts on a 32-bit boundary.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="lists">Lists</a> </div>
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<div class="doc_text">
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<p>Most blocks are constructed of lists of information. Lists can be constructed
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of other lists, etc. This decomposition of information follows the containment
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hierarchy of the LLVM Intermediate Representation. For example, a function
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contains a list of instructions (the terminator instructions implicitly define
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the end of the basic blocks).</p>
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<p>A list is encoded into the file simply by encoding the number of entries as
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an integer followed by each of the entries. The reader knows when the list is
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done because it will have filled the list with the required numbe of entries.
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</p>
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<p>LLVM Bytecode blocks often contain lists of things of a similar type. For
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example, a function contains a list of instructions and a function type
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contains a list of argument types. There are two basic types of lists:
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length lists, and null terminated lists, as described here:</p>
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<ul>
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<li><b>Length Lists</b>. Length lists are simply preceded by the number
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of items in the list. The bytecode reader will read the count first and
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then iterate that many times to read in the list contents.</li>
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<li><b>Null Terminated Lists</b>. For some lists, the number of elements
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in the list is not readily available at the time of writing the bytecode.
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In these cases, the list is terminated by some null value. What constitutes
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a null value differs, but it almost always boils down to a zero value.</li>
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</ul>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="fields">Fields</a> </div>
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<div class="doc_text">
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@ -129,46 +134,16 @@ they must contain. As few bits as possible are written for each field. The
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sections that follow will provide the details on how these fields are
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written and how the bits are to be interpreted.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="slots">Slots</a> </div>
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<div class="doc_subsection"><a name="align">Alignment</a> </div>
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<div class="doc_text">
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<p>The bytecode format uses the notion of a "slot" to reference Types and
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Values. Since the bytecode file is a <em>direct</em> representation of LLVM's
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intermediate representation, there is a need to represent pointers in the file.
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Slots are used for this purpose. For example, if one has the following assembly:
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</p>
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<div class="doc_code">
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%MyType = type { int, sbyte }<br>
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%MyVar = external global %MyType
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<p>To support cross-platform differences, the bytecode file is aligned on
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certain boundaries. This means that a small amount of padding (at most 3
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bytes) will be added to ensure that the next entry is aligned to a 32-bit
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boundary.</p>
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</div>
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<p>there are two definitions. The definition of <tt>%MyVar</tt> uses
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<tt>%MyType</tt>. In the C++ IR this linkage between <tt>%MyVar</tt> and
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<tt>%MyType</tt> is
|
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explicit through the use of C++ pointers. In bytecode, however, there's no
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ability to store memory addresses. Instead, we compute and write out slot
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numbers for every type and Value written to the file.</p>
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<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
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bit rate scheme (see <a href="#encoding">encoding</a> below). This ensures that
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low slot numbers are encoded in one byte. Through various bits of magic LLVM
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attempts to always keep the slot numbers low. The first attempt is to associate
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slot numbers with their "type plane". That is, Values of the same type are
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written to the bytecode file in a list (sequentially). Their order in that list
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determines their slot number. This means that slot #1 doesn't mean anything
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unless you also specify for which type you want slot #1. Types are handled
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specially and are always written to the file first (in the Global Type Pool) and
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in such a way that both forward and backward references of the types can often be
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resolved with a single pass through the type pool. </p>
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||||
<p>Slot numbers are also kept small by rearranging their order. Because of the
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structure of LLVM, certain values are much more likely to be used frequently
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in the body of a function. For this reason, a compaction table is provided in
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the body of a function if its use would make the function body smaller.
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Suppose you have a function body that uses just the types "int*" and "{double}"
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but uses them thousands of time. Its worthwhile to ensure that the slot number
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for these types are low so they can be encoded in a single byte (via vbr).
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This is exactly what the compaction table does.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
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<div class="doc_text">
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@ -219,80 +194,196 @@ variable bit rate encoding as described above.</p>
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<table class="doc_table" >
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<tr>
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<th><b>Type</b></th>
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<th align="left"><b>Rule</b></th>
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<th class="td_left"><b>Rule</b></th>
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</tr>
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<tr>
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<td>unsigned</td>
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<td align="left">A 32-bit unsigned integer that always occupies four
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<td><a name="unsigned">unsigned</a></td>
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<td class="td_left">A 32-bit unsigned integer that always occupies four
|
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consecutive bytes. The unsigned integer is encoded using LSB first
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ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the
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byte with the lowest file offset (little endian).</td>
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</tr><tr>
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<td>uint_vbr</td>
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<td align="left">A 32-bit unsigned integer that occupies from one to five
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<td><a name="uint_vbr">uint_vbr</a></td>
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<td class="td_left">A 32-bit unsigned integer that occupies from one to five
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bytes using variable bit rate encoding.</td>
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</tr><tr>
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<td>uint64_vbr</td>
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<td align="left">A 64-bit unsigned integer that occupies from one to ten
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<td><a name="uint64_vbr">uint64_vbr</a></td>
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<td class="td_left">A 64-bit unsigned integer that occupies from one to ten
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bytes using variable bit rate encoding.</td>
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</tr><tr>
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<td>int64_vbr</td>
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<td align="left">A 64-bit signed integer that occupies from one to ten
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<td><a name="int64_vbr">int64_vbr</a></td>
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<td class="td_left">A 64-bit signed integer that occupies from one to ten
|
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bytes using the signed variable bit rate encoding.</td>
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</tr><tr>
|
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<td>char</td>
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<td align="left">A single unsigned character encoded into one byte</td>
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<td><a name="char">char</a></td>
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<td class="td_left">A single unsigned character encoded into one byte</td>
|
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</tr><tr>
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<td>bit</td>
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||||
<td align="left">A single bit within a byte.</td>
|
||||
<td><a name="bit">bit</a></td>
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<td class="td_left">A single bit within some larger integer field.</td>
|
||||
</tr><tr>
|
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<td>string</td>
|
||||
<td align="left">A uint_vbr indicating the length of the character string
|
||||
<td><a name="string">string</a></td>
|
||||
<td class="td_left">A uint_vbr indicating the length of the character string
|
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immediately followed by the characters of the string. There is no
|
||||
terminating null byte in the string.</td>
|
||||
</tr><tr>
|
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<td>data</td>
|
||||
<td align="left">An arbitrarily long segment of data to which no
|
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<td><a name="data">data</a></td>
|
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<td class="td_left">An arbitrarily long segment of data to which no
|
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interpretation is implied. This is used for float, double, and constant
|
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initializers.</td>
|
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</tr><tr>
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<td><a name="block">block</a></td>
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<td class="td_left">A block of data that is logically related. A block
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begins with an <a href="#unsigned">unsigned</a> that provides the block
|
||||
identifier (constant value) and an <a href="#unsigned">unsigned</a> that
|
||||
provides the length of the block. Blocks may compose other blocks.
|
||||
</td>
|
||||
</tr>
|
||||
</table>
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||||
</div>
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||||
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="align">Alignment</a> </div>
|
||||
<div class="doc_subsection"><a name="slots">Slots</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To support cross-platform differences, the bytecode file is aligned on
|
||||
certain boundaries. This means that a small amount of padding (at most 3 bytes)
|
||||
will be added to ensure that the next entry is aligned to a 32-bit boundary.
|
||||
<p>The bytecode format uses the notion of a "slot" to reference Types and
|
||||
Values. Since the bytecode file is a <em>direct</em> representation of LLVM's
|
||||
intermediate representation, there is a need to represent pointers in the file.
|
||||
Slots are used for this purpose. For example, if one has the following assembly:
|
||||
</p>
|
||||
<div class="doc_code">
|
||||
%MyType = type { int, sbyte }<br>
|
||||
%MyVar = external global %MyType
|
||||
</div>
|
||||
<p>there are two definitions. The definition of <tt>%MyVar</tt> uses
|
||||
<tt>%MyType</tt>. In the C++ IR this linkage between <tt>%MyVar</tt> and
|
||||
<tt>%MyType</tt> is
|
||||
explicit through the use of C++ pointers. In bytecode, however, there's no
|
||||
ability to store memory addresses. Instead, we compute and write out slot
|
||||
numbers for every Type and Value written to the file.</p>
|
||||
<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
|
||||
bit rate scheme (see <a href="#encoding">encoding</a>). This ensures that
|
||||
low slot numbers are encoded in one byte. Through various bits of magic LLVM
|
||||
attempts to always keep the slot numbers low. The first attempt is to associate
|
||||
slot numbers with their "type plane". That is, Values of the same type are
|
||||
written to the bytecode file in a list (sequentially). Their order in that list
|
||||
determines their slot number. This means that slot #1 doesn't mean anything
|
||||
unless you also specify for which type you want slot #1. Types are handled
|
||||
specially and are always written to the file first (in the
|
||||
<a href="#globaltypes">Global Type Pool</a>) and
|
||||
in such a way that both forward and backward references of the types can often be
|
||||
resolved with a single pass through the type pool. </p>
|
||||
<p>Slot numbers are also kept small by rearranging their order. Because of the
|
||||
structure of LLVM, certain values are much more likely to be used frequently
|
||||
in the body of a function. For this reason, a compaction table is provided in
|
||||
the body of a function if its use would make the function body smaller.
|
||||
Suppose you have a function body that uses just the types "int*" and "{double}"
|
||||
but uses them thousands of time. Its worthwhile to ensure that the slot number
|
||||
for these types are low so they can be encoded in a single byte (via vbr).
|
||||
This is exactly what the compaction table does.</p>
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_section"> <a name="general">General Layout</a> </div>
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_text">
|
||||
<p>This section provides the general layout of the LLVM bytecode file format.
|
||||
The detailed layout can be found in the <a href="#details">next section</a>.
|
||||
</p>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="structure">Structure</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>The bytecode file format requires blocks to be in a certain order and
|
||||
nested in a particular way so that an LLVM module can be constructed
|
||||
efficiently from the contents of the file. This ordering defines a general
|
||||
structure for bytecode files as shown below. The table below shows the order
|
||||
in which all block types may appear. Please note that some of the blocks are
|
||||
optional and some may be repeated. The structure is fairly loose because
|
||||
optional blocks, if empty, are completely omitted from the file.
|
||||
</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th>ID</th>
|
||||
<th>Parent</th>
|
||||
<th>Optional?</th>
|
||||
<th>Repeated?</th>
|
||||
<th>Level</th>
|
||||
<th>Block Type</th>
|
||||
</tr>
|
||||
<tr><td>N/A</td><td>File</td><td>No</td><td>No</td><td>0</td>
|
||||
<td class="td_left"><a href="#signature">Signature</a></td>
|
||||
</tr>
|
||||
<tr><td>0x01</td><td>File</td><td>No</td><td>No</td><td>0</td>
|
||||
<td class="td_left"><a href="#module">Module</a></td>
|
||||
</tr>
|
||||
<tr><td>0x15</td><td>Module</td><td>No</td><td>No</td><td>1</td>
|
||||
<td class="td_left">
|
||||
<a href="#globaltypes">Global Type Pool</a></td>
|
||||
</tr>
|
||||
<tr><td>0x14</td><td>Module</td><td>No</td><td>No</td><td>1</td>
|
||||
<td class="td_left">
|
||||
<a href="#globalinfo">Module Globals Info</a></td>
|
||||
</tr>
|
||||
<tr><td>0x12</td><td>Module</td><td>Yes</td><td>No</td><td>1</td>
|
||||
<td class="td_left">
|
||||
<a href="#constantpool">Module Constant Pool</a></td>
|
||||
</tr>
|
||||
<tr><td>0x11</td><td>Module</td><td>Yes</td><td>Yes</td><td>1</td>
|
||||
<td class="td_left">
|
||||
<a href="#functiondefs">Function Definitions</a></td>
|
||||
</tr>
|
||||
<tr><td>0x12</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
|
||||
<td class="td_left">
|
||||
<a href="#constantpool">Function Constant Pool</a></td>
|
||||
</tr>
|
||||
<tr><td>0x33</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
|
||||
<td class="td_left">
|
||||
<a href="#compactiontable">Compaction Table</a></td>
|
||||
</tr>
|
||||
<tr><td>0x32</td><td>Function</td><td>No</td><td>No</td><td>2</td>
|
||||
<td class="td_left">
|
||||
<a href="#instructionlist">Instruction List</a></td>
|
||||
</tr>
|
||||
<tr><td>0x13</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
|
||||
<td class="td_left">
|
||||
<a href="#symboltable">Function Symbol Table</a></td>
|
||||
</tr>
|
||||
<tr><td>0x13</td><td>Module</td><td>Yes</td><td>No</td><td>1</td>
|
||||
<td class="td_left">
|
||||
<a href="#symboltable">Module Symbol Table</a></td>
|
||||
</tr>
|
||||
</table>
|
||||
<p>Use the links in the table or see <a href="#blocktypes">Block Types</a> for
|
||||
details about the contents of each of the block types.</p>
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_section"> <a name="details">Detailed Layout</a> </div>
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_text">
|
||||
<p>This section provides the detailed layout of the LLVM bytecode file format.
|
||||
bit and byte level specifics.</p>
|
||||
</p>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="notation">Notation</a></div>
|
||||
<div class="doc_text">
|
||||
<p>The descriptions of the bytecode format that follow describe the bit
|
||||
fields in detail. These descriptions are provided in tabular form. Each table
|
||||
has four columns that specify:</p>
|
||||
<ol>
|
||||
<li><b>Byte(s)</b>: The offset in bytes of the field from the start of
|
||||
its container (block, list, other field).</li>
|
||||
<li><b>Bit(s)</b>: The offset in bits of the field from the start of
|
||||
the byte field. Bits are always little endian. That is, bit addresses with
|
||||
smaller values have smaller address (i.e. 2<sup>0</sup> is at bit 0,
|
||||
2<sup>1</sup> at 1, etc.)
|
||||
</li>
|
||||
<li><b>Align?</b>: Indicates if this field is aligned to 32 bits or not.
|
||||
This indicates where the <em>next</em> field starts, always on a 32 bit
|
||||
boundary.</li>
|
||||
<li><b>Type</b>: The basic type of information contained in the field.</li>
|
||||
<li><b>Description</b>: Describes the contents of the field.</li>
|
||||
</ol>
|
||||
<p>The descriptions of the bytecode format that follow describe the order, type
|
||||
and bit fields in detail. These descriptions are provided in tabular form.
|
||||
Each table has four columns that specify:</p>
|
||||
<ol>
|
||||
<li><b>Byte(s)</b>: The offset in bytes of the field from the start of
|
||||
its container (block, list, other field).</li>
|
||||
<li><b>Bit(s)</b>: The offset in bits of the field from the start of
|
||||
the byte field. Bits are always little endian. That is, bit addresses with
|
||||
smaller values have smaller address (i.e. 2<sup>0</sup> is at bit 0,
|
||||
2<sup>1</sup> at 1, etc.)
|
||||
</li>
|
||||
<li><b>Align?</b>: Indicates if this field is aligned to 32 bits or not.
|
||||
This indicates where the <em>next</em> field starts, always on a 32 bit
|
||||
boundary.</li>
|
||||
<li><b>Type</b>: The basic type of information contained in the field.</li>
|
||||
<li><b>Description</b>: Describes the contents of the field.</li>
|
||||
</ol>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="blocktypes">Block Types</a></div>
|
||||
@ -330,90 +421,109 @@ other blocks because there is no identifier and no block length at the start
|
||||
of the block. Essentially, this block is just the "magic number" for the file.
|
||||
<table class="doc_table_nw" >
|
||||
<tr>
|
||||
<th><b>Byte(s)</b></th>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Align?</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th align="left"><b>Field Description</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td>00</td><td>-</td><td>No</td><td>char</td>
|
||||
<td align="left">Constant "l" (0x6C)</td>
|
||||
<td><a href="#char">char</a></td>
|
||||
<td class="td_left">Constant "l" (0x6C)</td>
|
||||
</tr><tr>
|
||||
<td>01</td><td>-</td><td>No</td><td>char</td>
|
||||
<td align="left">Constant "l" (0x6C)</td>
|
||||
<td><a href="#char">char</a></td>
|
||||
<td class="td_left">Constant "l" (0x6C)</td>
|
||||
</tr><tr>
|
||||
<td>02</td><td>-</td><td>No</td><td>char</td>
|
||||
<td align="left">Constant "v" (0x76)</td>
|
||||
<td><a href="#char">char</a></td>
|
||||
<td class="td_left">Constant "v" (0x76)</td>
|
||||
</tr><tr>
|
||||
<td>03</td><td>-</td><td>No</td><td>char</td>
|
||||
<td align="left">Constant "m" (0x6D)</td>
|
||||
<td><a href="#char">char</a></td>
|
||||
<td class="td_left">Constant "m" (0x6D)</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="module">Module Block</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>The module block contains a small pre-amble and all the other blocks in
|
||||
the file. Of particular note, the bytecode format number is simply a 28-bit
|
||||
monotonically increase integer that identifiers the version of the bytecode
|
||||
the file. The table below shows the structure of the module block. Note that it
|
||||
only provides the module identifier, size of the module block, and the format
|
||||
information. Everything else is contained in other blocks, described in other
|
||||
sections.</p>
|
||||
<table class="doc_table_nw" >
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Module Identifier (0x01)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size of the module block in bytes</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left"><a href="#format">Format Information</a></td>
|
||||
</tr><tr>
|
||||
<td><a href="#block">block</a></td>
|
||||
<td class="td_left"><a href="#globaltypes">Global Type Pool</a></td>
|
||||
</tr><tr>
|
||||
<td><a href="#block">block</a></td>
|
||||
<td class="td_left"><a href="#globalinfo">Module Globals Info</a></td>
|
||||
</tr><tr>
|
||||
<td><a href="#block">block</a></td>
|
||||
<td class="td_left"><a href="#constantpool">Module Constant Pool</a></td>
|
||||
</tr><tr>
|
||||
<td><a href="#block">block</a></td>
|
||||
<td class="td_left"><a href="#functiondefs">Function Definitions</a></td>
|
||||
</tr><tr>
|
||||
<td><a href="#block">block</a></td>
|
||||
<td class="td_left"><a href="#symboltable">Module Symbol Table</a></td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection"><a name="format">Format Information</a></div>
|
||||
<div class="doc_text">
|
||||
<p>The format information field is encoded into a 32-bit vbr-encoded unsigned
|
||||
integer as shown in the following table.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td>0</td><td>bit</td>
|
||||
<td class="td_left">Big Endian?</td>
|
||||
</tr><tr>
|
||||
<td>1</td><td>bit</td>
|
||||
<td class="td_left">Pointers Are 64-bit?</td>
|
||||
</tr><tr>
|
||||
<td>2</td><td>bit</td>
|
||||
<td class="td_left">Has No Endianess?</td>
|
||||
</tr><tr>
|
||||
<td>3</td><td>bit</td>
|
||||
<td class="td_left">Has No Pointer Size?</td>
|
||||
</tr><tr>
|
||||
<td>4-31</td><td>bit</td>
|
||||
<td class="td_left">Bytecode Format Version</td>
|
||||
</tr>
|
||||
</table>
|
||||
<p>
|
||||
Of particular note, the bytecode format number is simply a 28-bit
|
||||
monotonically increase integer that identifies the version of the bytecode
|
||||
format (which is not directly related to the LLVM release number). The
|
||||
bytecode versions defined so far are (note that this document only describes
|
||||
the latest version): </p>
|
||||
|
||||
the latest version, 1.3):</p>
|
||||
<ul>
|
||||
<li>#0: LLVM 1.0 & 1.1</li>
|
||||
<li>#1: LLVM 1.2</li>
|
||||
<li>#2: LLVM 1.3</li>
|
||||
</ul>
|
||||
|
||||
<p>The table below shows the format of the module block header. It is defined
|
||||
by blocks described in other sections.</p>
|
||||
<table class="doc_table_nw" >
|
||||
<tr>
|
||||
<th><b>Byte(s)</b></th>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Align?</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th align="left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td>04-07</td><td>-</td><td>No</td><td>unsigned</td>
|
||||
<td align="left">Module Identifier (0x01)</td>
|
||||
</tr><tr>
|
||||
<td>08-11</td><td>-</td><td>No</td><td>unsigned</td>
|
||||
<td align="left">Size of the module block in bytes</td>
|
||||
</tr><tr>
|
||||
<td>12-15</td><td>00</td><td>Yes</td><td>uint32_vbr</td>
|
||||
<td align="left">Format Information</td>
|
||||
</tr><tr>
|
||||
<td>''</td><td>0</td><td>-</td><td>bit</td>
|
||||
<td align="left">Big Endian?</td>
|
||||
</tr><tr>
|
||||
<td>''</td><td>1</td><td>-</td><td>bit</td>
|
||||
<td align="left">Pointers Are 64-bit?</td>
|
||||
</tr><tr>
|
||||
<td>''</td><td>2</td><td>-</td><td>bit</td>
|
||||
<td align="left">Has No Endianess?</td>
|
||||
</tr><tr>
|
||||
<td>''</td><td>3</td><td>-</td><td>bit</td>
|
||||
<td align="left">Has No Pointer Size?</td>
|
||||
</tr><tr>
|
||||
<td>''</td><td>4-31</td><td>-</td><td>bit</td>
|
||||
<td align="left">Bytecode Format Version</td>
|
||||
</tr><tr>
|
||||
<td>16-end</td><td>-</td><td>-</td><td>blocks</td>
|
||||
<td align="left">The remaining bytes in the block consist
|
||||
solely of other block types in sequence.</td>
|
||||
</tr>
|
||||
</table>
|
||||
|
||||
<p>Note that we plan to eventually expand the target description capabilities
|
||||
of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
|
||||
triples</a>.</p>
|
||||
|
||||
of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target triples</a>.
|
||||
</p>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="gtypepool">Global Type Pool</a> </div>
|
||||
<div class="doc_subsection"><a name="globaltypes">Global Type Pool</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>The global type pool consists of type definitions. Their order of appearance
|
||||
in the file determines their slot number (0 based). Slot numbers are used to
|
||||
@ -423,48 +533,161 @@ Since all values have types and are associated with the order in which the type
|
||||
pool is written, the global type pool <em>must</em> be written as the first
|
||||
block of a module. If it is not, attempts to read the file will fail because
|
||||
both forward and backward type resolution will not be possible.</p>
|
||||
<p>The type pool is simply a list of types definitions, as shown in the table
|
||||
<p>The type pool is simply a list of type definitions, as shown in the table
|
||||
below.</p>
|
||||
<table class="doc_table_nw" >
|
||||
<tr>
|
||||
<th><b>Byte(s)</b></th>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Align?</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th align="left"><b>Field Description</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td>00-03</td><td>-</td><td>No</td><td>unsigned</td>
|
||||
<td align="left">Type Pool Identifier (0x13)</td>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Type Pool Identifier (0x13)</td>
|
||||
</tr><tr>
|
||||
<td>04-07</td><td>-</td><td>No</td><td>unsigned</td>
|
||||
<td align="left">Size in bytes of the symbol table block.</td>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size in bytes of the symbol table block.</td>
|
||||
</tr><tr>
|
||||
<td>08-11<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
|
||||
<td align="left">Number of entries in type plane</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Number of entries in type plane</td>
|
||||
</tr><tr>
|
||||
<td>12-15<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
|
||||
<td align="left">Type plane index for following entries</td>
|
||||
<td><a href="#type">type</a></td>
|
||||
<td class="td_left">Each of the type definitions (see below)<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td>16-end<sup>1,2</sup></td><td>-</td><td>No</td><td>type</td>
|
||||
<td align="left">Each of the type definitions.</td>
|
||||
</tr><tr>
|
||||
<td align="left" colspan="5"><sup>1</sup>Maximum length shown,
|
||||
may be smaller<br><sup>2</sup>Repeated field.
|
||||
<td class="td_left" colspan="2">
|
||||
<sup>1</sup>Repeated field.<br/>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="modinfo">Module Info</a> </div>
|
||||
<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
|
||||
<div class="doc_text">
|
||||
<p>Types in the type pool are defined using a different format for each
|
||||
basic type of type as given in the following sections.</p>
|
||||
<h3>Primitive Types</h3>
|
||||
<p>The primitive types encompass the basic integer and floating point types</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID For The Primitive (1-11)<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td class="td_left" colspan="2">
|
||||
<sup>1</sup>See the definition of Type::TypeID in Type.h for the numeric
|
||||
equivalents of the primitive type ids.<br/>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3>Function Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID for function types (13)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of function's return type.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">The number of arguments in the function.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of each argument's type.<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Value 0 if this is a varargs function.<sup>2</sup></td>
|
||||
</tr><tr>
|
||||
<td class="td_left" colspan="2">
|
||||
<sup>1</sup>Repeated field.<br/>
|
||||
<sup>2</sup>Optional field.
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3>Structure Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID for structure types (14)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of each of the element's fields.<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Null Terminator (VoidTy type id)</td>
|
||||
</tr><tr>
|
||||
<td class="td_left" colspan="2">
|
||||
<sup>1</sup>Repeated field.<br/>
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3>Array Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID for Array Types (15)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of array's element type.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">The number of elements in the array.</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3>Pointer Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID For Pointer Types (16)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of pointer's element type.</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3>Opaque Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID For Opaque Types (17)</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="globalinfo">Module Global Info</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="constants">Constants</a> </div>
|
||||
<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="functions">Functions</a> </div>
|
||||
<div class="doc_subsection"><a name="functiondefs">Function Definition</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="compactiontable">Compaction Table</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="instructionlist">Instruction List</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
</div>
|
||||
@ -483,28 +706,28 @@ format is given in the table below. </p>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Align?</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th align="left"><b>Field Description</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td>00-03</td><td>-</td><td>No</td><td>unsigned</td>
|
||||
<td align="left">Symbol Table Identifier (0x13)</td>
|
||||
<td class="td_left">Symbol Table Identifier (0x13)</td>
|
||||
</tr><tr>
|
||||
<td>04-07</td><td>-</td><td>No</td><td>unsigned</td>
|
||||
<td align="left">Size in bytes of the symbol table block.</td>
|
||||
<td class="td_left">Size in bytes of the symbol table block.</td>
|
||||
</tr><tr>
|
||||
<td>08-11<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
|
||||
<td align="left">Number of entries in type plane</td>
|
||||
<td class="td_left">Number of entries in type plane</td>
|
||||
</tr><tr>
|
||||
<td>12-15<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
|
||||
<td align="left">Type plane index for following entries</td>
|
||||
<td class="td_left">Type plane index for following entries</td>
|
||||
</tr><tr>
|
||||
<td>16-19<sup>1,2</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
|
||||
<td align="left">Slot number of a value.</td>
|
||||
<td class="td_left">Slot number of a value.</td>
|
||||
</tr><tr>
|
||||
<td>variable<sup>1,2</sup></td><td>-</td><td>No</td><td>string</td>
|
||||
<td align="left">Name of the value in the symbol table.</td>
|
||||
<td class="td_left">Name of the value in the symbol table.</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td align="left" colspan="5"><sup>1</sup>Maximum length shown,
|
||||
<td class="td_left" colspan="5"><sup>1</sup>Maximum length shown,
|
||||
may be smaller<br><sup>2</sup>Repeated field.
|
||||
</tr>
|
||||
</table>
|
||||
@ -522,22 +745,60 @@ describes the differences between that version and the one that <i>follows</i>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection">
|
||||
<a name="vers12">Version 1.2 Differences From 1.3</a></div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection">Type Derives From Value</div>
|
||||
<div class="doc_text">
|
||||
<p>TBD: How version 1.2 differs from version 1.3</p>
|
||||
<p>In version 1.2, the Type class in the LLVM IR derives from the Value class.
|
||||
This is not the case in version 1.3. Consequently, in version 1.2 the notion
|
||||
of a "Type Type" was used to write out values that were Types. The types
|
||||
always occuped plane 12 (corresponding to the TypeTyID) of any type planed
|
||||
set of values. In 1.3 this representation is not convenient because the
|
||||
TypeTyID (12) is not present and its value is now used for LabelTyID.
|
||||
Consequently, the data structures written that involve types do so by writing
|
||||
all the types first and then each of the value planes according to those
|
||||
types. In version 1.2, the types would have been written intermingled with
|
||||
the values.</p>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection">Restricted getelementptr Types</a></div>
|
||||
<div class="doc_text">
|
||||
<p>In version 1.2, the getelementptr instruction required a ubyte type index
|
||||
for accessing a structure field and a long type index for accessing an array
|
||||
element. Consequently, it was only possible to access structures of 255 or
|
||||
fewer elements. Starting in version 1.3, this restriction was lifted.
|
||||
Structures must now be indexed with int or uint types. Arrays must now be
|
||||
indexed with long or ulong types. This requirement was needed so that LLVM
|
||||
could compile several test cases that used large numbers of fields in their
|
||||
structures. The consequence of this was that the bytecode format had to
|
||||
change in order to accommodate the larger range of structure indices.</p>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection">
|
||||
<a name="vers11">Version 1.1 Differences From 1.2 </a></div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection">Explicit Primitive Zeros</div>
|
||||
<div class="doc_text">
|
||||
<p>TBD: How version 1.1 differs from version 1.2</p>
|
||||
<p>In version 1.1, the zero value for primitives was explicitly encoded into
|
||||
the bytecode format. Since these zero values are constant values in the
|
||||
LLVM IR and never change, there is no reason to explicitly encode them. This
|
||||
explicit encoding was removed in version 1.2.</p>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection">Inconsistent Module Global Info</div>
|
||||
<div class="doc_text">
|
||||
<p>In version 1.1, the Module Global Info block was not aligned causing the
|
||||
next block to be read in on an unaligned boundary. This problem was corrected
|
||||
in version 1.2.</p>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection">
|
||||
<a name="vers11">Version 1.0 Differences From 1.1</a></div>
|
||||
<div class="doc_text">
|
||||
<p>TBD: How version 1.0 differs from version 1.1</p>
|
||||
<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
|
||||
Loading…
Reference in New Issue
Block a user