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1636 lines
62 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>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
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the binary encoding rules of the bytecode file format so that
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equivalent systems can encode bytecode files correctly. The LLVM
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bytecode representation is used to store the intermediate
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representation on disk in compacted form.</p>
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<p>The LLVM bytecode format may change in the future, but LLVM will
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always be backwards compatible with older formats. This document will
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only describe the most current version of the bytecode format. See <a
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href="#versiondiffs">Version Differences</a> for the details on how
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the current version is different from previous versions.</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
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format without getting into specific layout details. It is recommended
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that you read this section thoroughly before interpreting the detailed
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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
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using a binary encoding Each block begins with an header of two
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unsigned integers. The first value identifies the type of block and the
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second value provides the size of the block in bytes. The block
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identifier is used because it is possible for entire blocks to be
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omitted from the file if they are empty. The block identifier helps the
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reader determine which kind of block is next in the file. Note that
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blocks can be nested within other blocks.</p>
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<p> All blocks are variable length, and the block header specifies the
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size of the block. All blocks begin on a byte index that is aligned to
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an even 32-bit boundary. That is, the first block is 32-bit aligned
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because it starts at offset 0. Each block is padded with zero fill
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bytes to ensure that 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
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type. For example, a function contains a list of instructions and a
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function type contains a list of argument types. There are two basic
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types of lists: length lists (<a href="#llist">llist</a>), and null
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terminated lists (<a href="#zlist">zlist</a>), as described below in
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the <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. Most
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fields have a uniform length or some kind of length indication built into their
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encoding. For example, a constant string (array of bytes) is written simply as
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the length followed by the characters. Although this is similar to a list,
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constant strings are treated atomically and are thus 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
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on certain boundaries. This means that a small amount of padding (at
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most 3 bytes) will be added to ensure that the next entry is aligned to
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a 32-bit 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>
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</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 scheme
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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
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each byte is used to indicate if more bytes follow. If (byte &
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0x80) is non-zero in any given byte, it means there is another byte
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immediately following that also contributes to the value. For the final
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byte (byte & 0x80) is false (the high bit is not set). In each byte
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only the low seven bits contribute to the value. Consequently 32-bit
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quantities can take from one to <em>five</em> bytes to encode. In
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general, smaller quantities will encode in fewer bytes, as follows:</p>
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<table>
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<tbody>
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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>
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<td>1</td>
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<td>0-6</td>
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<td>127</td>
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</tr>
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<tr>
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<td>2</td>
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<td>7-13</td>
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<td>16,383</td>
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</tr>
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<tr>
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<td>3</td>
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<td>14-20</td>
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<td>2,097,151</td>
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</tr>
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<tr>
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<td>4</td>
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<td>21-27</td>
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<td>268,435,455</td>
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</tr>
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<tr>
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<td>5</td>
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<td>28-34</td>
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<td>34,359,738,367</td>
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</tr>
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<tr>
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<td>6</td>
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<td>35-41</td>
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<td>4,398,046,511,103</td>
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</tr>
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<tr>
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<td>7</td>
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<td>42-48</td>
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<td>562,949,953,421,311</td>
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</tr>
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<tr>
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<td>8</td>
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<td>49-55</td>
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<td>72,057,594,037,927,935</td>
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</tr>
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<tr>
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<td>9</td>
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<td>56-62</td>
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<td>9,223,372,036,854,775,807</td>
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</tr>
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<tr>
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<td>10</td>
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<td>63-69</td>
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<td>1,180,591,620,717,411,303,423</td>
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</tr>
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</tbody>
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</table>
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<p>Note that in practice, the tenth byte could only encode bit 63 since
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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
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encoding, but with the sign bit as the low order bit instead of the
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high order bit. This allows small negative quantities to be encoded
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efficiently. For example, -3
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is encoded as "((3 << 1) | 1)" and 3 is encoded as "(3 <<
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1) | 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
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small set of primitive formats. The table below defines the encoding
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rules for the various primitives used and gives them each a type name.
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The type names used in the descriptions of blocks and fields in the <a
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href="#details">Detailed Layout</a>next section. Any type name with
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the suffix <em>_vbr</em> indicates 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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<tbody>
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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>
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<tr>
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<td style="vertical-align: top;"><a name="uint24_vbr"><b>uint24_vbr</b></a></td>
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<td style="vertical-align: top; text-align: left;">A 24-bit unsigned
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integer that occupies from one to four bytes using variable bit rate
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encoding.</td>
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</tr>
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<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
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five bytes using variable bit rate encoding.</td>
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</tr>
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<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>
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<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>
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<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>
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<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 values
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of <code>n</code> and <code>m</code> specify the inclusive range of bits
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that define the subfield. The value for <code>m</code> may be omitted if
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its the same as <code>n</code>.</td>
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</tr>
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<tr>
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<td style="vertical-align: top;"><b><a name="float"><b>float</b></a></b></td>
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<td style="vertical-align: top; text-align: left;">A floating point value encoded
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as a 32-bit IEEE value written in little-endian form.<br>
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</td>
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</tr>
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<tr>
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<td style="vertical-align: top;"><b><b><a name="double"><b>double</b></a></b></b></td>
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<td style="vertical-align: top; text-align: left;">A floating point value encoded
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as a64-bit IEEE value written in little-endian form</td>
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</tr>
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<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
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constant string which also includes its length, immediately followed by
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the characters of the string. There is no terminating null byte in the
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string.</td>
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</tr>
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<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
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no interpretation is implied. This is used for constant initializers.<br>
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</td>
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</tr>
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<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
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encoded as an <a href="#uint32_vbr">uint32_vbr</a> providing the
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length of the list, followed by a sequence of that many "x" items. This
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implies that the reader should iterate the number of times provided by
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the length.</td>
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</tr>
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<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
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list is encoded as a sequence of an indeterminate number of "x" items,
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followed by an <a href="#uint32_vbr">uint32_vbr</a> terminating value.
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This implies that none of the "x" items can have a zero value (or else
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the list terminates).</td>
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</tr>
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<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
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block is an unsigned 32-bit integer that encodes the type of the block
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in the low 5 bits and the size of the block in the high 27 bits. The
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length does not include the block header or any alignment bytes at the
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end of the block. Blocks may compose other blocks. </td>
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</tr>
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</tbody>
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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
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like notation is used to describe optional and repeated fields. A very
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limited subset of regex is used to describe these, as given in the
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following table: </p>
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<table class="doc_table">
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<tbody>
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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>
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<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
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occurrences of the thing preceding it.</td>
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</tr>
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<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
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of the thing preceding it.</td>
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</tr>
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<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
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of the thing preceding it.</td>
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</tr>
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<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>
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<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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</tbody>
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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>
|
|
<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
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|
uint32_vbr 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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|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsection"><a name="slots">Slots</a> </div>
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|
<div class="doc_text">
|
|
<p>The bytecode format uses the notion of a "slot" to reference Types
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|
and Values. Since the bytecode file is a <em>direct</em> representation of
|
|
LLVM's intermediate representation, there is a need to represent pointers in
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|
the file. Slots are used for this purpose. For example, if one has the following
|
|
assembly:
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|
</p>
|
|
<div class="doc_code"><code> %MyType = type { int, sbyte }<br>
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|
%MyVar = external global %MyType
|
|
</code></div>
|
|
<p>there are two definitions. The definition of <tt>%MyVar</tt> uses <tt>%MyType</tt>.
|
|
In the C++ IR this linkage between <tt>%MyVar</tt> and <tt>%MyType</tt>
|
|
is explicit through the use of C++ pointers. In bytecode, however, there's no
|
|
ability to store memory addresses. Instead, we compute and write out
|
|
slot numbers for every Type and Value written to the file.</p>
|
|
<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
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|
bit rate scheme (see <a href="#encoding">encoding</a>). This ensures that
|
|
low slot numbers are encoded in one byte. Through various bits of magic LLVM
|
|
attempts to always keep the slot numbers low. The first attempt is to associate
|
|
slot numbers with their "type plane". That is, Values of the same type
|
|
are written to the bytecode file in a list (sequentially). Their order in
|
|
that list determines their slot number. This means that slot #1 doesn't mean
|
|
anything unless you also specify for which type you want slot #1. Types are
|
|
handled specially and are always written to the file first (in the <a
|
|
href="#globaltypes">Global Type Pool</a>) and in such a way that both forward
|
|
and backward references of the types can often be resolved with a single pass
|
|
through the type pool. </p>
|
|
<p>Slot numbers are also kept small by rearranging their order. Because
|
|
of the structure of LLVM, certain values are much more likely to be used
|
|
frequently in the body of a function. For this reason, a compaction table is
|
|
provided in the body of a function if its use would make the function body
|
|
smaller. Suppose you have a function body that uses just the types "int*" and
|
|
"{double}" but uses them thousands of time. Its worthwhile to ensure that the
|
|
slot number for these types are low so they can be encoded in a single byte
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|
(via vbr). This is exactly what the compaction table does.</p>
|
|
</div>
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_section"> <a name="general">General Structure</a> </div>
|
|
<!-- *********************************************************************** -->
|
|
<div class="doc_text">
|
|
<p>This section provides the general structure of the LLVM bytecode
|
|
file format. The bytecode file format requires blocks to be in a
|
|
certain order and nested in a particular way so that an LLVM module can
|
|
be constructed efficiently from the contents of the file. This ordering
|
|
defines a general structure for bytecode files as shown below. The
|
|
table below shows the order in which all block types may appear. Please
|
|
note that some of the blocks are optional and some may be repeated. The
|
|
structure is fairly loose because optional blocks, if empty, are
|
|
completely omitted from the file.</p>
|
|
<table>
|
|
<tbody>
|
|
<tr>
|
|
<th>ID</th>
|
|
<th>Parent</th>
|
|
<th>Optional?</th>
|
|
<th>Repeated?</th>
|
|
<th>Level</th>
|
|
<th>Block Type</th>
|
|
<th>Description</th>
|
|
</tr>
|
|
<tr>
|
|
<td>N/A</td>
|
|
<td>File</td>
|
|
<td>No</td>
|
|
<td>No</td>
|
|
<td>0</td>
|
|
<td class="td_left"><a href="#signature">Signature</a></td>
|
|
<td class="td_left">This contains the file signature (magic
|
|
number) that identifies the file as LLVM bytecode.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>0x01</td>
|
|
<td>File</td>
|
|
<td>No</td>
|
|
<td>No</td>
|
|
<td>0</td>
|
|
<td class="td_left"><a href="#module">Module</a></td>
|
|
<td class="td_left">This is the top level block in a bytecode
|
|
file. It contains all the other blocks. </td>
|
|
</tr>
|
|
<tr>
|
|
<td>0x06</td>
|
|
<td>Module</td>
|
|
<td>No</td>
|
|
<td>No</td>
|
|
<td>1</td>
|
|
<td class="td_left"> <a href="#globaltypes">Global Type Pool</a></td>
|
|
<td class="td_left">This block contains all the global (module)
|
|
level types.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>0x05</td>
|
|
<td>Module</td>
|
|
<td>No</td>
|
|
<td>No</td>
|
|
<td>1</td>
|
|
<td class="td_left"> <a href="#globalinfo">Module Globals Info</a></td>
|
|
<td class="td_left">This block contains the type, constness, and
|
|
linkage for each of the global variables in the module. It also
|
|
contains the type of the functions and the constant initializers.</td>
|
|
</tr>
|
|
<tr>
|
|
<td>0x03</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>0x02</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>0x03</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>0x08</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>0x07</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>0x04</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>0x04</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>
|
|
</tbody>
|
|
</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.
|
|
</p>
|
|
<table>
|
|
<tbody>
|
|
<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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#block">block</a><br>
|
|
</td>
|
|
<td class="td_left">Module Block Identifier (0x01) and Size<br>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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>
|
|
</tbody>
|
|
</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 1.2.5 (not released)</li>
|
|
<li>#3: LLVM 1.3<br>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#unsigned">block</a></td>
|
|
<td class="td_left">Type Pool Identifier (0x06) + Size<br>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Type ID for the primitive types (values 1 to
|
|
11) <sup>1</sup></td>
|
|
</tr>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Type ID for function types (13)</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_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="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</table>
|
|
<h3>Structure Types</h3>
|
|
<table>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Type ID for structure types (14)</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#zlist">zlist</a>(<a href="#uint24_vbr">uint24_vbr</a>)</td>
|
|
<td class="td_left">Slot number of each of the element's fields.</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<h3>Array Types</h3>
|
|
<table>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Type ID for Array Types (15)</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</table>
|
|
<h3>Pointer Types</h3>
|
|
<table>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Type ID For Pointer Types (16)</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Slot number of pointer's element type.</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<h3>Opaque Types</h3>
|
|
<table>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint24_vbr">uint24_vbr</a></td>
|
|
<td class="td_left">Type ID For Opaque Types (17)</td>
|
|
</tr>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#block">block</a></td>
|
|
<td class="td_left">Module global info identifier (0x05) + size<br>
|
|
</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="#uint24_vbr">uint24_vbr</a>)</td>
|
|
<td class="td_left">A zero terminated list of function types
|
|
occuring in the module.</td>
|
|
</tr>
|
|
<tr>
|
|
<td style="vertical-align: top;"><a href="#llist">llist</a>(<a
|
|
href="#string">string</a>)<br>
|
|
</td>
|
|
<td style="vertical-align: top; text-align: left;">A length list
|
|
of strings that specify the names of the libraries that this module
|
|
depends upon.<br>
|
|
</td>
|
|
</tr>
|
|
<tr>
|
|
<td style="vertical-align: top;"><a href="#string">string</a><br>
|
|
</td>
|
|
<td style="vertical-align: top; text-align: left;">The target
|
|
triple for the module (blank means no target triple specified, i.e. a
|
|
platform independent module).<br>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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. </td>
|
|
</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>
|
|
</tbody>
|
|
</table>
|
|
<p>The table below provides the format of the constant initializers for
|
|
the global variable field, if it has one.</p>
|
|
<table>
|
|
<tbody>
|
|
<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>))?
|
|
</td>
|
|
<td class="td_left">An optional zero-terminated list of slot
|
|
numbers of the global variable's constant initializer.</td>
|
|
</tr>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#block">block</a></td>
|
|
<td class="td_left">Constant pool identifier (0x03) + size<br>
|
|
</td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p><b>Module Constant Pool Preamble (constant strings)</b></p>
|
|
<table>
|
|
<tbody>
|
|
<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="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</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>
|
|
<p><b>Common Part (other constants)</b></p>
|
|
<table>
|
|
<tbody>
|
|
<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="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#block">block</a><br>
|
|
</td>
|
|
<td class="td_left">Function definition block identifier (0x02) +
|
|
size<br>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#block">block</a><br>
|
|
</td>
|
|
<td class="td_left">Instruction list identifier (0x07) + size<br>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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="#uint24_vbr">uint24_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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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>
|
|
</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#block">block</a><br>
|
|
</td>
|
|
<td class="td_left">Symbol Table Identifier (0x04)</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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<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>
|
|
</tbody>
|
|
</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>
|
|
<tbody>
|
|
<tr>
|
|
<th><b>Type</b></th>
|
|
<th class="td_left"><b>Field Description</b></th>
|
|
</tr>
|
|
<tr>
|
|
<td><a href="#uint32_vbr">uint24_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>
|
|
</tbody>
|
|
</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</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_subsubsection">Short Block Headers</div>
|
|
<div class="doc_text">
|
|
<p>In version 1.2, block headers were always 8 bytes being comprised of
|
|
both an unsigned integer type and an unsigned integer size. For very
|
|
small modules, these block headers turn out to be a large fraction of
|
|
the total bytecode file size. In an attempt to make these small files
|
|
smaller, the type and size information was encoded into a single
|
|
unsigned integer (4 bytes) comprised of 5 bits for the block type
|
|
(maximum 31 block types) and 27 bits for the block size (max
|
|
~134MBytes). These limits seemed sufficient for any blocks or sizes
|
|
forseen in the future. Note that the module block, which encloses all
|
|
the other blocks is still written as 8 bytes since bytecode files
|
|
larger than 134MBytes might be possible.</p>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">Dependent Libraries and Target Triples</div>
|
|
<div class="doc_text">
|
|
<p>In version 1.2, the bytecode format does not store module's target
|
|
triple or dependent. These fields have been added to the end of the <a
|
|
href="#globalinfo">module global info block</a>. The purpose of these
|
|
fields is to allow a front end compiler to specifiy that the generated
|
|
module is specific to a particular target triple (operating
|
|
system/manufacturer/processor) which makes it non-portable; and to
|
|
allow front end compilers to specify the list of libraries that the
|
|
module depends on for successful linking.</p>
|
|
</div>
|
|
<!-- _______________________________________________________________________ -->
|
|
<div class="doc_subsubsection">Types Restricted to 24-bits</div>
|
|
<div class="doc_text">
|
|
<p>In version 1.2, type slot identifiers were written as 32-bit VBR
|
|
quantities. In 1.3 this has been reduced to 24-bits in order to ensure
|
|
that it is not possible to overflow the type field of a global variable
|
|
definition. 24-bits for type slot numbers is deemed sufficient for any
|
|
practical use of LLVM.</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.<br>
|
|
<br>
|
|
</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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<a href="http://validator.w3.org/check/referer"><img
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src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
|
|
<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: $Date$
|
|
</address>
|
|
<!-- vim: sw=2
|
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-->
|
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</body>
|
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