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- 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
821 lines
36 KiB
HTML
821 lines
36 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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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="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;
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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="#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="#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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<ol>
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<li><a href="#notation">Notation</a></li>
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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="#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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<ol>
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<li><a href="#vers12">Version 1.2 Differences From 1.3</a></li>
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<li><a href="#vers11">Version 1.1 Differences From 1.2</a></li>
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<li><a href="#vers10">Version 1.0 Differences From 1.1</a></li>
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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>
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</p>
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</div>
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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 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="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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without getting into bit and byte level specifics. Note that the LLVM bytecode
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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 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 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>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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<p>Fields are units of information that LLVM knows how to write atomically.
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Most fields have a uniform length or some kind of length indication built into
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their encoding. For example, a constant string (array of bytes) is
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written simply as the length followed by the characters. Although this is
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similar to a list, constant strings are treated atomically and are thus
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fields.</p>
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<p>Fields use a condensed bit format specific to the type of information
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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="align">Alignment</a> </div>
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<div class="doc_text">
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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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<!-- _______________________________________________________________________ -->
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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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<p>Each field that can be put out is encoded into the file using a small set
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of primitives. The rules for these primitives are described below.</p>
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<h3>Variable Bit Rate Encoding</h3>
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<p>Most of the values written to LLVM bytecode files are small integers. To
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minimize the number of bytes written for these quantities, an encoding
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scheme similar to UTF-8 is used to write integer data. The scheme is known as
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variable bit rate (vbr) encoding. In this encoding, the high bit of each
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byte is used to indicate if more bytes follow. If (byte & 0x80) is non-zero
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in any given byte, it means there is another byte immediately following that
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also contributes to the value. For the final byte (byte & 0x80) is false
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(the high bit is not set). In each byte only the low seven bits contribute to
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the value. Consequently 32-bit quantities can take from one to <em>five</em>
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bytes to encode. In general, smaller quantities will encode in fewer bytes,
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as follows:</p>
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<table class="doc_table_nw">
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<tr>
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<th>Byte #</th>
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<th>Significant Bits</th>
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<th>Maximum Value</th>
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</tr>
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<tr><td>1</td><td>0-6</td><td>127</td></tr>
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<tr><td>2</td><td>7-13</td><td>16,383</td></tr>
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<tr><td>3</td><td>14-20</td><td>2,097,151</td></tr>
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<tr><td>4</td><td>21-27</td><td>268,435,455</td></tr>
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<tr><td>5</td><td>28-34</td><td>34,359,738,367</td></tr>
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<tr><td>6</td><td>35-41</td><td>4,398,046,511,103</td></tr>
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<tr><td>7</td><td>42-48</td><td>562,949,953,421,311</td></tr>
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<tr><td>8</td><td>49-55</td><td>72,057,594,037,927,935</td></tr>
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<tr><td>9</td><td>56-62</td><td>9,223,372,036,854,775,807</td></tr>
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<tr><td>10</td><td>63-69</td><td>1,180,591,620,717,411,303,423</td></tr>
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</table>
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<p>Note that in practice, the tenth byte could only encode bit 63
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since the maximum quantity to use this encoding is a 64-bit integer.</p>
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<p><em>Signed</em> VBR values are encoded with the standard vbr encoding, but
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with the sign bit as the low order bit instead of the high order bit. This
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allows small negative quantities to be encoded efficiently. For example, -3
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is encoded as "((3 << 1) | 1)" and 3 is encoded as "(3 << 1) |
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0)", emitted with the standard vbr encoding above.</p>
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<p>The table below defines the encoding rules for type names used in the
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descriptions of blocks and fields in the next section. Any type name with
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the suffix <em>_vbr</em> indicate a quantity that is encoded using
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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 class="td_left"><b>Rule</b></th>
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</tr>
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<tr>
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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><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><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><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><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><a name="bit">bit</a></td>
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<td class="td_left">A single bit within some larger integer field.</td>
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</tr><tr>
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<td><a name="string">string</a></td>
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<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
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terminating null byte in the string.</td>
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</tr><tr>
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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
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identifier (constant value) and an <a href="#unsigned">unsigned</a> that
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provides the length of the block. Blocks may compose other blocks.
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</td>
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</tr>
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</table>
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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_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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</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>). 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
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<a href="#globaltypes">Global Type Pool</a>) 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_section"> <a name="general">General Layout</a> </div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This section provides the general layout of the LLVM bytecode file format.
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The detailed layout can be found in the <a href="#details">next section</a>.
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</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="structure">Structure</a> </div>
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<div class="doc_text">
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<p>The bytecode file format requires blocks to be in a certain order and
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nested in a particular way so that an LLVM module can be constructed
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efficiently from the contents of the file. This ordering defines a general
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structure for bytecode files as shown below. The table below shows the order
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in which all block types may appear. Please note that some of the blocks are
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optional and some may be repeated. The structure is fairly loose because
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optional blocks, if empty, are completely omitted from the file.
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</p>
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<table>
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<tr>
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<th>ID</th>
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<th>Parent</th>
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<th>Optional?</th>
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<th>Repeated?</th>
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<th>Level</th>
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<th>Block Type</th>
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</tr>
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<tr><td>N/A</td><td>File</td><td>No</td><td>No</td><td>0</td>
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<td class="td_left"><a href="#signature">Signature</a></td>
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</tr>
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<tr><td>0x01</td><td>File</td><td>No</td><td>No</td><td>0</td>
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<td class="td_left"><a href="#module">Module</a></td>
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</tr>
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<tr><td>0x15</td><td>Module</td><td>No</td><td>No</td><td>1</td>
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<td class="td_left">
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<a href="#globaltypes">Global Type Pool</a></td>
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</tr>
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<tr><td>0x14</td><td>Module</td><td>No</td><td>No</td><td>1</td>
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<td class="td_left">
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<a href="#globalinfo">Module Globals Info</a></td>
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</tr>
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<tr><td>0x12</td><td>Module</td><td>Yes</td><td>No</td><td>1</td>
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<td class="td_left">
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<a href="#constantpool">Module Constant Pool</a></td>
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</tr>
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<tr><td>0x11</td><td>Module</td><td>Yes</td><td>Yes</td><td>1</td>
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<td class="td_left">
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<a href="#functiondefs">Function Definitions</a></td>
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</tr>
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<tr><td>0x12</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
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<td class="td_left">
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<a href="#constantpool">Function Constant Pool</a></td>
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</tr>
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<tr><td>0x33</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
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<td class="td_left">
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<a href="#compactiontable">Compaction Table</a></td>
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</tr>
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<tr><td>0x32</td><td>Function</td><td>No</td><td>No</td><td>2</td>
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<td class="td_left">
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<a href="#instructionlist">Instruction List</a></td>
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</tr>
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<tr><td>0x13</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
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<td class="td_left">
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<a href="#symboltable">Function Symbol Table</a></td>
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|
</tr>
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<tr><td>0x13</td><td>Module</td><td>Yes</td><td>No</td><td>1</td>
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<td class="td_left">
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<a href="#symboltable">Module Symbol Table</a></td>
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|
</tr>
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|
</table>
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|
<p>Use the links in the table or see <a href="#blocktypes">Block Types</a> for
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details about the contents of each of the block types.</p>
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</div>
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<!-- *********************************************************************** -->
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|
<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.
|
|
</p>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
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|
<div class="doc_subsection"><a name="notation">Notation</a></div>
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|
<div class="doc_text">
|
|
<p>The descriptions of the bytecode format that follow describe the order, type
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and bit fields in detail. These descriptions are provided in tabular form.
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|
Each table has four columns that specify:</p>
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|
<ol>
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<li><b>Byte(s)</b>: The offset in bytes of the field from the start of
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its container (block, list, other field).</li>
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|
<li><b>Bit(s)</b>: The offset in bits of the field from the start of
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the byte field. Bits are always little endian. That is, bit addresses with
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|
smaller values have smaller address (i.e. 2<sup>0</sup> is at bit 0,
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2<sup>1</sup> at 1, etc.)
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</li>
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<li><b>Align?</b>: Indicates if this field is aligned to 32 bits or not.
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|
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>
|
|
<div class="doc_text">
|
|
<p>The bytecode format encodes the intermediate representation into groups
|
|
of bytes known as blocks. The blocks are written sequentially to the file in
|
|
the following order:</p>
|
|
<ol>
|
|
<li><a href="#signature">Signature</a>: This contains the file signature
|
|
(magic number) that identifies the file as LLVM bytecode and the bytecode
|
|
version number.</li>
|
|
<li><a href="#module">Module Block</a>: This is the top level block in a
|
|
bytecode file. It contains all the other blocks.</li>
|
|
<li><a href="#gtypepool">Global Type Pool</a>: This block contains all the
|
|
global (module) level types.</li>
|
|
<li><a href="#modinfo">Module Info</a>: This block contains the types of the
|
|
global variables and functions in the module as well as the constant
|
|
initializers for the global variables</li>
|
|
<li><a href="#constants">Constants</a>: This block contains all the global
|
|
constants except function arguments, global values and constant strings.</li>
|
|
<li><a href="#functions">Functions</a>: One function block is written for
|
|
each function in the module. </li>
|
|
<li><a href="#symtab">Symbol Table</a>: The module level symbol table that
|
|
provides names for the various other entries in the file is the final block
|
|
written.</li>
|
|
</ol>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="signature">Signature Block</a> </div>
|
|
<div class="doc_text">
|
|
<p>The signature occurs in every LLVM bytecode file and is always first.
|
|
It simply provides a few bytes of data to identify the file as being an LLVM
|
|
bytecode file. This block is always four bytes in length and differs from the
|
|
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>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#char">char</a></td>
|
|
<td class="td_left">Constant "l" (0x6C)</td>
|
|
</tr><tr>
|
|
<td><a href="#char">char</a></td>
|
|
<td class="td_left">Constant "l" (0x6C)</td>
|
|
</tr><tr>
|
|
<td><a href="#char">char</a></td>
|
|
<td class="td_left">Constant "v" (0x76)</td>
|
|
</tr><tr>
|
|
<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. 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, 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>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>
|
|
</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
|
|
replace pointers in the intermediate representation. Each slot number uniquely
|
|
identifies one entry in a type plane (a collection of values of the same type).
|
|
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 type definitions, as shown in the table
|
|
below.</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">Type Pool Identifier (0x13)</td>
|
|
</tr><tr>
|
|
<td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Size in bytes of the symbol table block.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Number of entries in type plane</td>
|
|
</tr><tr>
|
|
<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 class="td_left" colspan="2">
|
|
<sup>1</sup>Repeated field.<br/>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
</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="constantpool">Constant Pool</a> </div>
|
|
<div class="doc_text">
|
|
<p>To be determined.</p>
|
|
</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>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
|
|
<div class="doc_text">
|
|
<p>A symbol table can be put out in conjunction with a module or a function.
|
|
A symbol table is a list of type planes. Each type plane starts with the number
|
|
of entries in the plane and the type plane's slot number (so the type can be
|
|
looked up in the global type pool). For each entry in a type plane, the slot
|
|
number of the value and the name associated with that value are written. The
|
|
format is given 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 class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td>00-03</td><td>-</td><td>No</td><td>unsigned</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 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 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 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 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 class="td_left">Name of the value in the symbol table.</td>
|
|
</tr>
|
|
<tr>
|
|
<td class="td_left" colspan="5"><sup>1</sup>Maximum length shown,
|
|
may be smaller<br><sup>2</sup>Repeated field.
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"> <a name="versiondiffs">Version Differences</a> </div>
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_text">
|
|
<p>This section describes the differences in the Bytecode Format across LLVM
|
|
versions. The versions are listed in reverse order because it assumes the
|
|
current version is as documented in the previous sections. Each section here
|
|
describes the differences between that version and the one that <i>follows</i>
|
|
</p>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<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>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>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>
|
|
|
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection">
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<a name="vers11">Version 1.0 Differences From 1.1</a></div>
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<div class="doc_text">
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<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
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<hr>
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<address>
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src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
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<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
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<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
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Last modified: $Date$
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