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1299 lines
57 KiB
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<!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-left: 4pt; padding-right: 4pt; padding-top: 2pt; padding-bottom: 2pt; }
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TH { border: 2px solid gray; font-weight: bold; font-size: 105%; }
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TABLE { text-align: center; 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; 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="#vbr">Variable Bit-Rate Encoding</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 Structure</a> </li>
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<li><a href="#blockdefs">Block Definitions</a>
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<ol>
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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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<!-- *********************************************************************** -->
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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. It specifies the
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binary encoding rules of the bytecode file format so that equivalent systems
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can encode bytecode files correctly. The LLVM bytecode representation is
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used to store the intermediate representation on disk in compacted form.</p>
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<p>The LLVM bytecode format may change in the future, but LLVM will always be
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backwards compatible with older formats. This document will only describe
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the most current version of the bytecode format. See
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<a href="#versiondiffs">Version Differences</a> for the details on how the
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current version is different from previous versions.</p>
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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 specific layout details. It is recommended that you read
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this section thoroughly before interpreting the detailed descriptions.</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 using
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a binary encoding Each block begins with an header of two unsigned integers.
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The first value identifies the type of block and the second value provides
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the size of the block in bytes. The block identifier is used because it is
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possible for entire blocks to be omitted from the file if they are empty.
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The block identifier helps the reader determine which kind of block is next
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in the file. Note that blocks can be nested within other blocks.</p>
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<p> All blocks are variable length, and the block header specifies the size
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of the block. All blocks begin on a byte index that is aligned to an even
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32-bit boundary. That is, the first block is 32-bit aligned because it
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starts at offset 0. Each block is padded with zero fill bytes to ensure that
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the next block also 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 (<a href="#llist">llist</a>), and null terminated lists
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(<a href="#zlist">zlist</a>), as described below in the
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<a href="#encoding">Encoding Primitives</a>.</p>
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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="vbr">Variable Bit-Rate Encoding</a> </div>
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<div class="doc_text">
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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>
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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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</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 in the bytecode format is encoded into the file using a small
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set of primitive formats. The table below defines the encoding rules for the
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various primitives used and gives them each a type name. The type names used
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in the descriptions of blocks and fields in the <a href="#details">Detailed
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Layout</a>next section. Any type name with the suffix <em>_vbr</em> indicates
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a quantity that is encoded using variable bit rate encoding as described
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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"><b>unsigned</b></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="uint32_vbr"><b>uint32_vbr</b></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"><b>uint64_vbr</b></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"><b>int64_vbr</b></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"><b>char</b></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"><b>bit(n-m)</b></a></td>
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<td class="td_left">A set of bit within some larger integer field. The
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values of <code>n</code> and <code>m</code> specify the inclusive range
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of bits that define the subfield. The value for <code>m</code> may be
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omitted if its the same as <code>n</code>.</td>
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</tr><tr>
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<td><a name="string"><b>string</b></a></td>
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<td class="td_left">A uint32_vbr indicating the type of the constant string
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which also includes its length, immediately followed by the characters of
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the string. There is no terminating null byte in the string.</td>
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</tr><tr>
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<td><a name="data"><b>data</b></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="llist"><b>llist(x)</b></a></td>
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<td class="td_left">A length list of x. This means the list is encoded as
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an <a href="#uint32_vbr">uint32_vbr</a> providing the length of the list,
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followed by a sequence of that many "x" items. This implies that the reader
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should iterate the number of times provided by the length.</td>
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</tr><tr>
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<td><a name="zlist"><b>zlist(x)</b></a></td>
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<td class="td_left">A zero-terminated list of x. This means the list is encoded
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as a sequence of an indeterminate number of "x" items, followed by an
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<a href="#uint32_vbr">uint32_vbr</a> terminating value. This implies that none
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of the "x" items can have a zero value (or else the list terminates).</td>
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</tr><tr>
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<td><a name="block"><b>block</b></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="notation">Field Notation</a> </div>
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<div class="doc_text">
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<p>In the detailed block and field descriptions that follow, a regex like
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notation is used to describe optional and repeated fields. A very limited
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subset of regex is used to describe these, as given in the following table:
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</p>
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<table class="doc_table" >
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<tr>
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<th><b>Character</b></th>
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<th class="td_left"><b>Meaning</b></th>
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</tr><tr>
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<td><b><code>?</code></b></td>
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<td class="td_left">The question mark indicates 0 or 1 occurrences of
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the thing preceding it.</td>
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</tr><tr>
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<td><b><code>*</code></b></td>
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<td class="td_left">The asterisk indicates 0 or more occurrences of the
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thing preceding it.</td>
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</tr><tr>
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<td><b><code>+</code></b></td>
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<td class="td_left">The plus sign indicates 1 or more occurrences of the
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thing preceding it.</td>
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</tr><tr>
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<td><b><code>()</code></b></td>
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<td class="td_left">Parentheses are used for grouping.</td>
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</tr><tr>
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<td><b><code>,</code></b></td>
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<td class="td_left">The comma separates sequential fields.</td>
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</tr>
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</table>
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<p>So, for example, consider the following specifications:</p>
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<div class="doc_code">
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<ol>
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<li><code>string?</code></li>
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<li><code>(uint32_vbr,uin32_vbr)+</code></li>
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<li><code>(unsigned?,uint32_vbr)*</code></li>
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<li><code>(llist(unsigned))?</code></li>
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</ol>
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</div>
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<p>with the following interpretations:</p>
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<ol>
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<li>An optional string. Matches either nothing or a single string</li>
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<li>One or more pairs of uint32_vbr.</li>
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<li>Zero or more occurrences of either an unsigned followed by a uint32_vbr
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or just a uint32_vbr.</li>
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<li>An optional length list of unsigned values.</li>
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</ol>
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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"><code>
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%MyType = type { int, sbyte }<br>
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%MyVar = external global %MyType
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</code></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>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"> <a name="general">General Structure</a> </div>
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|
<!-- *********************************************************************** -->
|
|
<div class="doc_text">
|
|
<p>This section provides the general structure of the LLVM bytecode file
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|
format. 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.</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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|
<th>Description</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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|
<td class="td_left">This contains the file signature (magic number)
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that identifies the file as LLVM bytecode.</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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|
<td class="td_left">This is the top level block in a bytecode file. It
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contains all the other blocks.</li>
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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"> <a href="#globaltypes">Global Type Pool</a></td>
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<td class="td_left">This block contains all the global (module) level
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types.</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"> <a href="#globalinfo">Module Globals Info</a></td>
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|
<td class="td_left">This block contains the type, constness, and linkage
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|
for each of the global variables in the module. It also contains the
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|
type of the functions and the constant initializers.</td>
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|
</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>
|
|
<td class="td_left">This block contains all the global constants
|
|
except function arguments, global values and constant strings.</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>
|
|
<td class="td_left">One function block is written for each function in
|
|
the module. The function block contains the instructions, compaction
|
|
table, type constant pool, and symbol table for the function.</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>
|
|
<td class="td_left">Any constants (including types) used solely
|
|
within the function are emitted here in the function constant pool.
|
|
</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>
|
|
<td class="td_left">This table reduces bytecode size by providing a
|
|
funtion-local mapping of type and value slot numbers to their
|
|
global slot numbers</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>
|
|
<td class="td_left">This block contains all the instructions of the
|
|
function. The basic blocks are inferred by terminating instructions.
|
|
</td>
|
|
</tr>
|
|
<tr><td>0x13</td><td>Function</td><td>Yes</td><td>No</td><td>2</td>
|
|
<td class="td_left"> <a href="#symtab">Function Symbol Table</a></td>
|
|
<td class="td_left">This symbol table provides the names for the
|
|
function specific values used (basic block labels mostly).</td>
|
|
</tr>
|
|
<tr><td>0x13</td><td>Module</td><td>Yes</td><td>No</td><td>1</td>
|
|
<td class="td_left"> <a href="#symtab">Module Symbol Table</a></td>
|
|
<td class="td_left">This symbol table provides the names for the various
|
|
entries in the file that are not function specific (global vars, and
|
|
functions mostly).</td>
|
|
</tr>
|
|
</table>
|
|
<p>Use the links in the table for details about the contents of each of the block types.</p>
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"> <a name="blockdefs">Block Definitions</a> </div>
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_text">
|
|
<p>This section provides the detailed layout of the individual block types
|
|
in the LLVM bytecode file format. </p>
|
|
</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>
|
|
<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>
|
|
<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
|
|
<a href="#uint32_vbr">uint32_vbr</a> as shown in the following table.</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(0)</a></td>
|
|
<td class="td_left">Target is big endian?</td>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(1)</a></td>
|
|
<td class="td_left">On target pointers are 64-bit?</td>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(2)</a></td>
|
|
<td class="td_left">Target has no endianess?</td>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(3)</a></td>
|
|
<td class="td_left">Target has no pointer size?</td>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(4-31)</a></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>
|
|
<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 (0x15)</td>
|
|
</tr><tr>
|
|
<td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Size in bytes of the type pool block.</td>
|
|
</tr><tr>
|
|
<td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
|
|
<td class="td_left">A length list of type definitions.</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 kind
|
|
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</a></td>
|
|
<td class="td_left">Type ID for the primitive types (values 1 to 11)
|
|
<sup>1</sup></td>
|
|
</tr>
|
|
</table>
|
|
Notes:
|
|
<ol>
|
|
<li>The values for the Type IDs for the primitive types are provided by the
|
|
definition of the <code>llvm::Type::TypeID</code> enumeration in
|
|
<code>include/llvm/Type.h</code>. The enumeration gives the following
|
|
mapping:<ol>
|
|
<li>bool</li>
|
|
<li>ubyte</li>
|
|
<li>sbyte</li>
|
|
<li>ushort</li>
|
|
<li>short</li>
|
|
<li>uint</li>
|
|
<li>int</li>
|
|
<li>ulong</li>
|
|
<li>long</li>
|
|
<li>float</li>
|
|
<li>double</li>
|
|
</ol></li>
|
|
</ol>
|
|
<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</a></td>
|
|
<td class="td_left">Type ID for function types (13)</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Slot number of function's return type.</td>
|
|
</tr><tr>
|
|
<td><a href="#llist">llist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
|
|
<td class="td_left">Slot number of each argument's type.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a>?</td>
|
|
<td class="td_left">Value 0 if this is a varargs function, missing otherwise.</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</a></td>
|
|
<td class="td_left">Type ID for structure types (14)</td>
|
|
</tr><tr>
|
|
<td><a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
|
|
<td class="td_left">Slot number of each of the element's fields.</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</a></td>
|
|
<td class="td_left">Type ID for Array Types (15)</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Slot number of array's element type.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></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</a></td>
|
|
<td class="td_left">Type ID For Pointer Types (16)</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></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</a></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>The module global info block contains the definitions of all global
|
|
variables including their initializers and the <em>declaration</em> of all
|
|
functions. The format is shown in the table below:</p>
|
|
<table>
|
|
<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 global info identifier (0x14)</td>
|
|
</tr><tr>
|
|
<td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Size in bytes of the module global info block.</td>
|
|
</tr><tr>
|
|
<td><a href="#zlist">zlist</a>(<a href="#globalvar">globalvar</a>)</td>
|
|
<td class="td_left">A zero terminated list of global var definitions
|
|
occuring in the module.</td>
|
|
</tr><tr>
|
|
<td><a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
|
|
<td class="td_left">A zero terminated list of function types occuring in
|
|
the module.</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
|
|
</div>
|
|
<div class="doc_text">
|
|
<p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
|
|
that encodes information about the global variable and a list of the constant
|
|
initializers for the global var, if any.</p>
|
|
<p>The table below provides the bit layout of the first
|
|
<a href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(0)</a></td>
|
|
<td class="td_left">Is constant?</td>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(1)</a></td>
|
|
<td class="td_left">Has initializer? Note that this bit determines whether
|
|
the constant initializer field (described below) follows.</li>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(2-4)</a></td>
|
|
<td class="td_left">Linkage type: 0=External, 1=Weak, 2=Appending,
|
|
3=Internal, 4=LinkOnce</td>
|
|
</tr><tr>
|
|
<td><a href="#bit">bit(5-31)</a></td>
|
|
<td class="td_left">Slot number of type for the global variable.</td>
|
|
</tr>
|
|
</table>
|
|
<p>The table below provides the format of the constant initializers for the
|
|
global variable field, if it has one.</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr><tr>
|
|
<td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
|
|
</a>
|
|
</td>
|
|
<td class="td_left">An optional zero-terminated list of slot numbers of
|
|
the global variable's constant initializer.</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
|
|
<div class="doc_text">
|
|
<p>A constant pool defines as set of constant values. There are actually two
|
|
types of constant pool blocks: one for modules and one for functions. For
|
|
modules, the block begins with the constant strings encountered anywhere in
|
|
the module. For functions, the block begins with types only encountered in
|
|
the function. In both cases the header is identical. The tables that follow,
|
|
show the header, module constant pool preamble, function constant pool
|
|
preamble, and the part common to both function and module constant pools.</p>
|
|
<p><b>Common Block Header</b></p>
|
|
<table>
|
|
<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">Constant pool identifier (0x12)</td>
|
|
</tr><tr>
|
|
<td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Size in bytes of the constant pool block.</td>
|
|
</tr>
|
|
</table>
|
|
<p><b>Module Constant Pool Preamble (constant strings)</b></p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">The number of constant strings that follow.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Zero. This identifies the following "plane" as
|
|
containing the constant strings. This is needed to identify it
|
|
uniquely from other constant planes that follow.
|
|
</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
|
<td class="td_left">Slot number of the constant string's type. Note
|
|
that the constant string's type implicitly defines the length of
|
|
the string.
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
<p><b>Function Constant Pool Preamble (function types)</b></p>
|
|
<p>The structure of the types for functions is identical to the
|
|
<a href="#globaltypes">Global Type Pool</a>. Please refer to that section
|
|
for the details.
|
|
<p><b>Common Part (other constants)</b></p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Number of entries in this type plane.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Type slot number of this plane.</td>
|
|
</tr><tr>
|
|
<td><a href="#constant">constant</a>+</td>
|
|
<td class="td_left">The definition of a constant (see below).</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
|
|
<div class="doc_text">
|
|
<p>Constants come in many shapes and flavors. The sections that followe define
|
|
the format for each of them. All constants start with a
|
|
<a href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the number
|
|
of operands for the constant. For primitive, structure, and array constants,
|
|
this will always be zero since those types of constants have no operands.
|
|
In this case, we have the following field definitions:</p>
|
|
<ul>
|
|
<li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a>
|
|
of value 1U or 0U.</li>
|
|
<li><b>Signed Integers (sbyte,short,int,long)</b>. These are written as
|
|
an <a href="#int64_vbr">int64_vbr</a> with the corresponding value.</li>
|
|
<li><b>Unsigned Integers (ubyte,ushort,uint,ulong)</b>. These are written
|
|
as an <a href="#uint64_vbr">uint64_vbr</a> with the corresponding value.
|
|
</li>
|
|
<li><b>Floating Point</b>. Both the float and double types are written
|
|
literally in binary format.</li>
|
|
<li><b>Arrays</b>. Arrays are written simply as a list of
|
|
<a href="#uint32_vbr">uint32_vbr</a> encoded slot numbers to the constant
|
|
element values.</li>
|
|
<li><b>Structures</b>. Structures are written simply as a list of
|
|
<a href="#uint32_vbr">uint32_vbr</a> encoded slot numbers to the constant
|
|
field values of the structure.</li>
|
|
</ul>
|
|
<p>When the number of operands to the constant is non-zero, we have a
|
|
constant expression and its field format is provided in the table below.</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Op code of the instruction for the constant
|
|
expression.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">The slot number of the constant value for an
|
|
operand.<sup>1</sup></td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">The slot number for the type of the constant value
|
|
for an operand.<sup>1</sup></td>
|
|
</tr>
|
|
</table>
|
|
Notes:<ol>
|
|
<li>Both these fields are repeatable but only in pairs.</li>
|
|
</ol>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
|
|
<div class="doc_text">
|
|
<p>Function definitions contain the linkage, constant pool or compaction
|
|
table, instruction list, and symbol table for a function. The following table
|
|
shows the structure of a function definition.</p>
|
|
<table>
|
|
<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">Function definition block identifier (0x11)</td>
|
|
</tr><tr>
|
|
<td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Size in bytes of the function definition block.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">The linkage type of the function: 0=External, 1=Weak,
|
|
2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></td>
|
|
</tr><tr>
|
|
<td><a href="#block">block</a></td>
|
|
<td class="td_left">The <a href="#constantpool">constant pool</a> block
|
|
for this function.<sup>2</sup></td>
|
|
</tr><tr>
|
|
<td><a href="#block">block</a></td>
|
|
<td class="td_left">The <a href="#compactiontable">compaction table</a>
|
|
block for the function.<sup>2</sup></td>
|
|
</tr><tr>
|
|
<td><a href="#block">block</a></td>
|
|
<td class="td_left">The <a href="#instructionlist">instruction list</a>
|
|
for the function.</td>
|
|
</tr><tr>
|
|
<td><a href="#block">block</a></td>
|
|
<td class="td_left">The function's <a href="#symboltable">symbol table</a>
|
|
containing only those symbols pertinent to the function (mostly
|
|
block labels).</td>
|
|
</tr>
|
|
</table>
|
|
Notes:<ol>
|
|
<li>Note that if the linkage type is "External" then none of the other
|
|
fields will be present as the function is defined elsewhere.</li>
|
|
<li>Note that only one of the constant pool or compaction table will be
|
|
written. Compaction tables are only written if they will actually save
|
|
bytecode space. If not, then a regular constant pool is written.</li>
|
|
</ol>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="compactiontable">Compaction Table</a> </div>
|
|
<div class="doc_text">
|
|
<p>Compaction tables are part of a function definition. They are merely a
|
|
device for reducing the size of bytecode files. The size of a bytecode
|
|
file is dependent on the <em>value</em> of the slot numbers used because
|
|
larger values use more bytes in the variable bit rate encoding scheme.
|
|
Furthermore, the compressed instruction format reserves only six bits for
|
|
the type of the instruction. In large modules, declaring hundreds or thousands
|
|
of types, the values of the slot numbers can be quite large. However,
|
|
functions may use only a small fraction of the global types. In such cases
|
|
a compaction table is created that maps the global type and value slot
|
|
numbers to smaller values used by a function. Functions will contain either
|
|
a function-specific constant pool <em>or</em> a compaction table but not
|
|
both. Compaction tables have the format shown in the table below.</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">The number of types that follow</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
|
<td class="td_left">The slot number in the global type plane of the
|
|
type that will be referenced in the function with the index of
|
|
this entry in the compaction table.</td>
|
|
</tr><tr>
|
|
<td><a href="#type_len">type_len</a></td>
|
|
<td class="td_left">An encoding of the type and number of values that
|
|
follow. This field's encoding varies depending on the size of
|
|
the type plane. See <a href="#type_len">Type and Length</a> for
|
|
further details.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
|
<td class="td_left">The slot number in the globals of the value that
|
|
will be referenced in the function with the index of this entry in
|
|
the compaction table</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection"><a name="type_len">Type and Length</a></div>
|
|
<div class="doc_text">
|
|
<p>The type and length of a compaction table type plane is encoded differently
|
|
depending on the length of the plane. For planes of length 1 or 2, the length
|
|
is encoded into bits 0 and 1 of a <a href="#uint32_vbr">uint32_vbr</a> and the
|
|
type is encoded into bits 2-31. Because type numbers are often small, this
|
|
often saves an extra byte per plane. If the length of the plane is greater
|
|
than 2 then the encoding uses a <a href="#uint32_vbr">uint32_vbr</a> for each
|
|
of the length and type, in that order.</p>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="instructionlist">Instruction List</a> </div>
|
|
<div class="doc_text">
|
|
<p>The instructions in a function are written as a simple list. Basic blocks
|
|
are inferred by the terminating instruction types. The format of the block
|
|
is given in the following table.</p>
|
|
<table>
|
|
<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">Instruction list identifier (0x33).</td>
|
|
</tr><tr>
|
|
<td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Size in bytes of the instruction list.</td>
|
|
</tr><tr>
|
|
<td><a href="#instruction">instruction</a>+</td>
|
|
<td class="td_left">An instruction. Instructions have a variety of formats.
|
|
See <a href="#instruction">Instructions</a> for details.</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection"><a name="instruction">Instructions</a></div>
|
|
<div class="doc_text">
|
|
<p>For brevity, instructions are written in one of four formats, depending on
|
|
the number of operands to the instruction. Each instruction begins with a
|
|
<a href="#uint32_vbr">uint32_vbr</a> that encodes the type of the instruction
|
|
as well as other things. The tables that follow describe the format of this
|
|
first word of each instruction.</p>
|
|
<p><b>Instruction Format 0</b></p>
|
|
<p>This format is used for a few instructions that can't easily be optimized
|
|
because they have large numbers of operands (e.g. PHI Node or getelementptr).
|
|
Each of the opcode, type, and operand fields is as successive fields.</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Specifies the opcode of the instruction. Note that for
|
|
compatibility with the other instruction formats, the opcode is shifted
|
|
left by 2 bits. Bits 0 and 1 must have value zero for this format.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Provides the slot number of the result type of the
|
|
instruction</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">The number of operands that follow.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
|
<td class="td_left">The slot number of the value(s) for the operand(s).
|
|
<sup>1</sup></td>
|
|
</tr>
|
|
</table>
|
|
Notes:<ol>
|
|
<li>Note that if the instruction is a getelementptr and the type of the
|
|
operand is a sequential type (array or pointer) then the slot number is
|
|
shifted up two bits and the low order bits will encode the type of index
|
|
used, as follows: 0=uint, 1=int, 2=ulong, 3=long.</li>
|
|
</ol>
|
|
<p><b>Instruction Format 1</b></p>
|
|
<p>This format encodes the opcode, type and a single operand into a single
|
|
<a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Bits</b></th>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td>0-1</td><td>constant "1"</td>
|
|
<td class="td_left">These two bits must be the value 1 which identifies
|
|
this as an instruction of format 1.</td>
|
|
</td>
|
|
</tr><tr>
|
|
<td>2-7</td><td><a href="#opcodes">opcode</a></td>
|
|
<td class="td_left">Specifies the opcode of the instruction. Note that
|
|
the maximum opcode value is 63.</td>
|
|
</tr><tr>
|
|
<td>8-19</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the type for this
|
|
instruction. Maximum slot number is 2<sup>12</sup>-1=4095.</td>
|
|
</tr><tr>
|
|
<td>20-31</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the value for the
|
|
first operand. Maximum slot number is 2<sup>12</sup>-1=4095. Note
|
|
that the value 2<sup>12</sup>-1 denotes zero operands.</td>
|
|
</tr>
|
|
</table>
|
|
<p><b>Instruction Format 2</b></p>
|
|
<p>This format encodes the opcode, type and two operands into a single
|
|
<a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Bits</b></th>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td>0-1</td><td>constant "2"</td>
|
|
<td class="td_left">These two bits must be the value 2 which identifies
|
|
this as an instruction of format 2.</td>
|
|
</td>
|
|
</tr><tr>
|
|
<td>2-7</td><td><a href="#opcodes">opcode</a></td>
|
|
<td class="td_left">Specifies the opcode of the instruction. Note that
|
|
the maximum opcode value is 63.</td>
|
|
</tr><tr>
|
|
<td>8-15</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the type for this
|
|
instruction. Maximum slot number is 2<sup>8</sup>-1=255.</td>
|
|
</tr><tr>
|
|
<td>16-23</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the value for the
|
|
first operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
|
|
</tr><tr>
|
|
<td>24-31</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the value for the
|
|
second operand. Maximum slot number is 2<sup>8</sup>-1=255.</td>
|
|
</tr>
|
|
</table>
|
|
<p><b>Instruction Format 3</b></p>
|
|
<p>This format encodes the opcode, type and three operands into a single
|
|
<a href="#uint32_vbr">uint32_vbr</a> as follows:</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Bits</b></th>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td>0-1</td><td>constant "3"</td>
|
|
<td class="td_left">These two bits must be the value 3 which identifies
|
|
this as an instruction of format 3.</td>
|
|
</td>
|
|
</tr><tr>
|
|
<td>2-7</td><td><a href="#opcodes">opcode</a></td>
|
|
<td class="td_left">Specifies the opcode of the instruction. Note that
|
|
the maximum opcode value is 63.</td>
|
|
</tr><tr>
|
|
<td>8-13</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the type for this
|
|
instruction. Maximum slot number is 2<sup>6</sup>-1=63.</td>
|
|
</tr><tr>
|
|
<td>14-19</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the value for the
|
|
first operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
|
|
</tr><tr>
|
|
<td>20-25</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the value for the
|
|
second operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
|
|
</tr><tr>
|
|
<td>26-31</td><td><a href="#unsigned">unsigned</a></td>
|
|
<td class="td_left">Specifies the slot number of the value for the
|
|
third operand. Maximum slot number is 2<sup>6</sup>-1=63.</td>
|
|
</tr>
|
|
</table>
|
|
</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>
|
|
<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">Symbol Table 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="#symtab_entry">symtab_entry</a>*</td>
|
|
<td class="td_left">Provides the slot number of the type and its name.</td>
|
|
</tr><tr>
|
|
<td><a href="#symtab_plane">symtab_plane</a>*</td>
|
|
<td class="td_left">A type plane containing value slot number and name
|
|
for all values of the same type.</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection"> <a name="symtab_plane">Symbol Table Plane</a>
|
|
</div>
|
|
<div class="doc_text">
|
|
<p>A symbol table plane provides the symbol table entries for all values of
|
|
a common type. The encoding is given in the following table:</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Number of entries in this plane.</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Slot number of type for this plane.</td>
|
|
</tr><tr>
|
|
<td><a href="#symtab_entry">symtab_entry</a>+</td>
|
|
<td class="td_left">The symbol table entries for this plane.</td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection"> <a name="symtab_entry">Symbol Table Entry</a>
|
|
</div>
|
|
<div class="doc_text">
|
|
<p>A symbol table entry provides the assocation between a type or value's
|
|
slot number and the name given to that type or value. The format is given
|
|
in the following table:</p>
|
|
<table>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Slot number of the type or value being given a name.
|
|
</td>
|
|
</tr><tr>
|
|
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
|
<td class="td_left">Length of the character array that follows.</td>
|
|
</tr><tr>
|
|
<td><a href="#char">char</a>+</td>
|
|
<td class="td_left">The characters of the name.</td>
|
|
</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 uint constants. Arrays may now be
|
|
indexed with int, uint, long, or ulong typed values.
|
|
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>
|
|
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection">
|
|
<a name="vers10">Version 1.0 Differences From 1.1</a></div>
|
|
<div class="doc_text">
|
|
<p>None. Version 1.0 and 1.1 bytecode formats are identical.</p>
|
|
</div>
|
|
|
|
<!-- *********************************************************************** -->
|
|
<hr>
|
|
<address>
|
|
<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
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src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!" /></a>
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|
|
<a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
|
|
<a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
|
|
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
|
|
Last modified: $Date$
|
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</address>
|
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