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5 <title>LLVM Bytecode File Format</title>
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13<body>
14 <div class="doc_title"> LLVM Bytecode File Format </div>
15<ol>
16 <li><a href="#abstract">Abstract</a></li>
Reid Spencer6f1d6992004-05-23 17:12:45 +0000[diff] [blame]17 <li><a href="#general">General Concepts</a>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]18 <ol>
19 <li><a href="#blocks">Blocks</a></li>
20 <li><a href="#lists">Lists</a></li>
21 <li><a href="#fields">Fields</a></li>
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]22 <li><a href="#slots">Slots</a></li>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]23 <li><a href="#encoding">Encoding Rules</a></li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]24 <li><a href="#align">Alignment</a></li>
25 </ol>
Reid Spencer6f1d6992004-05-23 17:12:45 +0000[diff] [blame]26 </li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]27 <li><a href="#details">Detailed Layout</a>
28 <ol>
29 <li><a href="#notation">Notation</a></li>
30 <li><a href="#blocktypes">Blocks Types</a></li>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]31 <li><a href="#signature">Signature Block</a></li>
32 <li><a href="#module">Module Block</a></li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]33 <li><a href="#typeool">Global Type Pool</a></li>
34 <li><a href="#modinfo">Module Info Block</a></li>
35 <li><a href="#constants">Global Constant Pool</a></li>
Chris Lattner2ca1fd12004-05-24 04:55:32 +0000[diff] [blame]36 <li><a href="#functions">Function Blocks</a></li>
37 <li><a href="#symtab">Module Symbol Table</a></li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]38 </ol>
39 </li>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]40 <li><a href="#versiondiffs">Version Differences</a>
41 <ol>
42 <li><a href="#vers12">Version 1.2 Differences From 1.3</a></li>
43 <li><a href="#vers11">Version 1.1 Differences From 1.2</a></li>
44 <li><a href="#vers10">Version 1.0 Differences From 1.1</a></li>
45 </ol>
46 </li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]47</ol>
Chris Lattner8dabb502004-05-25 17:44:58 +0000[diff] [blame]48<div class="doc_author">
49<p>Written by <a href="mailto:rspencer@x10sys.com">Reid Spencer</a>
50</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]51</div>
Reid Spencerc0a2af12004-06-05 14:18:02 +0000[diff] [blame]52<div class="doc_warning">
53 <p>Warning: This is a work in progress.</p>
54</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]55<!-- *********************************************************************** -->
56<div class="doc_section"> <a name="abstract">Abstract </a></div>
57<!-- *********************************************************************** -->
58<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]59<p>This document describes the LLVM bytecode
60file format. It specifies the binary encoding rules of the bytecode file format
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]61so that equivalent systems can encode bytecode files correctly. The LLVM
62bytecode representation is used to store the intermediate representation on
63disk in compacted form.
64</p>
65</div>
66<!-- *********************************************************************** -->
67<div class="doc_section"> <a name="general">General Concepts</a> </div>
68<!-- *********************************************************************** -->
69<div class="doc_text">
70<p>This section describes the general concepts of the bytecode file format
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]71without getting into bit and byte level specifics. Note that the LLVM bytecode
72format may change in the future, but will always be backwards compatible with
73older formats. This document only describes the most current version of the
74bytecode format.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]75</div>
76<!-- _______________________________________________________________________ -->
77<div class="doc_subsection"><a name="blocks">Blocks</a> </div>
78<div class="doc_text">
79<p>LLVM bytecode files consist simply of a sequence of blocks of bytes.
80Each block begins with an identification value that determines the type of
81the next block. The possible types of blocks are described below in the section
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]82<a href="#blocktypes">Block Types</a>. The block identifier is used because
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]83it is possible for entire blocks to be omitted from the file if they are
84empty. The block identifier helps the reader determine which kind of block is
85next in the file.</p>
Reid Spencer939290f2004-05-22 05:56:41 +0000[diff] [blame]86<p>The following block identifiers are currently in use
87(from llvm/Bytecode/Format.h):</p>
88<ol>
89 <li><b>Module (0x01)</b>.</li>
90 <li><b>Function (0x11)</b>.</li>
91 <li><b>ConstantPool (0x12)</b>.</li>
92 <li><b>SymbolTable (0x13)</b>.</li>
93 <li><b>ModuleGlobalInfo (0x14)</b>.</li>
94 <li><b>GlobalTypePlane (0x15)</b>.</li>
95 <li><b>BasicBlock (0x31)</b>.</li>
96 <li><b>InstructionList (0x32)</b>.</li>
97 <li><b>CompactionTable (0x33)</b>.</li>
98</ol>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]99<p> All blocks are variable length, and the block header specifies the size of
100the block. All blocks are rounded aligned to even 32-bit boundaries, so they
101always start and end of this boundary. Each block begins with an integer
102identifier and the length of the block, which does not include the padding
103bytes needed for alignment.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]104</div>
105<!-- _______________________________________________________________________ -->
106<div class="doc_subsection"><a name="lists">Lists</a> </div>
107<div class="doc_text">
108<p>Most blocks are constructed of lists of information. Lists can be constructed
109of other lists, etc. This decomposition of information follows the containment
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]110hierarchy of the LLVM Intermediate Representation. For example, a function
111contains a list of instructions (the terminator instructions implicitly define
112the end of the basic blocks).</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]113<p>A list is encoded into the file simply by encoding the number of entries as
114an integer followed by each of the entries. The reader knows when the list is
115done because it will have filled the list with the required numbe of entries.
116</p>
117</div>
118<!-- _______________________________________________________________________ -->
119<div class="doc_subsection"><a name="fields">Fields</a> </div>
120<div class="doc_text">
121<p>Fields are units of information that LLVM knows how to write atomically.
122Most fields have a uniform length or some kind of length indication built into
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]123their encoding. For example, a constant string (array of bytes) is
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]124written simply as the length followed by the characters. Although this is
125similar to a list, constant strings are treated atomically and are thus
126fields.</p>
127<p>Fields use a condensed bit format specific to the type of information
128they must contain. As few bits as possible are written for each field. The
129sections that follow will provide the details on how these fields are
130written and how the bits are to be interpreted.</p>
131</div>
132<!-- _______________________________________________________________________ -->
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]133<div class="doc_subsection"><a name="slots">Slots</a> </div>
134<div class="doc_text">
135<p>The bytecode format uses the notion of a "slot" to reference Types and
136Values. Since the bytecode file is a <em>direct</em> representation of LLVM's
137intermediate representation, there is a need to represent pointers in the file.
138Slots are used for this purpose. For example, if one has the following assembly:
139</p>
Chris Lattner8dabb502004-05-25 17:44:58 +0000[diff] [blame]140
141<div class="doc_code">
142 %MyType = type { int, sbyte }<br>
143 %MyVar = external global %MyType
144</div>
145
146<p>there are two definitions. The definition of <tt>%MyVar</tt> uses
147<tt>%MyType</tt>. In the C++ IR this linkage between <tt>%MyVar</tt> and
148<tt>%MyType</tt> is
149explicit through the use of C++ pointers. In bytecode, however, there's no
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]150ability to store memory addresses. Instead, we compute and write out slot
151numbers for every type and Value written to the file.</p>
152<p>A slot number is simply an unsigned 32-bit integer encoded in the variable
153bit rate scheme (see <a href="#encoding">encoding</a> below). This ensures that
154low slot numbers are encoded in one byte. Through various bits of magic LLVM
155attempts to always keep the slot numbers low. The first attempt is to associate
156slot numbers with their "type plane". That is, Values of the same type are
157written to the bytecode file in a list (sequentially). Their order in that list
158determines their slot number. This means that slot #1 doesn't mean anything
159unless you also specify for which type you want slot #1. Types are handled
160specially and are always written to the file first (in the Global Type Pool) and
Chris Lattner8dabb502004-05-25 17:44:58 +0000[diff] [blame]161in such a way that both forward and backward references of the types can often be
Reid Spencer7aa940d2004-05-25 15:47:57 +0000[diff] [blame]162resolved with a single pass through the type pool. </p>
163<p>Slot numbers are also kept small by rearranging their order. Because of the
164structure of LLVM, certain values are much more likely to be used frequently
165in the body of a function. For this reason, a compaction table is provided in
166the body of a function if its use would make the function body smaller.
167Suppose you have a function body that uses just the types "int*" and "{double}"
168but uses them thousands of time. Its worthwhile to ensure that the slot number
169for these types are low so they can be encoded in a single byte (via vbr).
170This is exactly what the compaction table does.</p>
171</div>
172<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]173<div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
174<div class="doc_text">
175<p>Each field that can be put out is encoded into the file using a small set
176of primitives. The rules for these primitives are described below.</p>
177<h3>Variable Bit Rate Encoding</h3>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]178<p>Most of the values written to LLVM bytecode files are small integers. To
179minimize the number of bytes written for these quantities, an encoding
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]180scheme similar to UTF-8 is used to write integer data. The scheme is known as
181variable bit rate (vbr) encoding. In this encoding, the high bit of each
182byte is used to indicate if more bytes follow. If (byte &amp; 0x80) is non-zero
183in any given byte, it means there is another byte immediately following that
184also contributes to the value. For the final byte (byte &amp; 0x80) is false
185(the high bit is not set). In each byte only the low seven bits contribute to
186the value. Consequently 32-bit quantities can take from one to <em>five</em>
187bytes to encode. In general, smaller quantities will encode in fewer bytes,
188as follows:</p>
189<table class="doc_table_nw">
190 <tr>
191 <th>Byte #</th>
192 <th>Significant Bits</th>
193 <th>Maximum Value</th>
194 </tr>
195 <tr><td>1</td><td>0-6</td><td>127</td></tr>
196 <tr><td>2</td><td>7-13</td><td>16,383</td></tr>
197 <tr><td>3</td><td>14-20</td><td>2,097,151</td></tr>
198 <tr><td>4</td><td>21-27</td><td>268,435,455</td></tr>
199 <tr><td>5</td><td>28-34</td><td>34,359,738,367</td></tr>
200 <tr><td>6</td><td>35-41</td><td>4,398,046,511,103</td></tr>
201 <tr><td>7</td><td>42-48</td><td>562,949,953,421,311</td></tr>
202 <tr><td>8</td><td>49-55</td><td>72,057,594,037,927,935</td></tr>
203 <tr><td>9</td><td>56-62</td><td>9,223,372,036,854,775,807</td></tr>
204 <tr><td>10</td><td>63-69</td><td>1,180,591,620,717,411,303,423</td></tr>
205</table>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]206<p>Note that in practice, the tenth byte could only encode bit 63
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]207since the maximum quantity to use this encoding is a 64-bit integer.</p>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]208
209<p><em>Signed</em> VBR values are encoded with the standard vbr encoding, but
210with the sign bit as the low order bit instead of the high order bit. This
211allows small negative quantities to be encoded efficiently. For example, -3
212is encoded as "((3 &lt;&lt; 1) | 1)" and 3 is encoded as "(3 &lt;&lt; 1) |
2130)", emitted with the standard vbr encoding above.</p>
214
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]215<p>The table below defines the encoding rules for type names used in the
216descriptions of blocks and fields in the next section. Any type name with
217the suffix <em>_vbr</em> indicate a quantity that is encoded using
218variable bit rate encoding as described above.</p>
219<table class="doc_table" >
220 <tr>
221 <th><b>Type</b></th>
222 <th align="left"><b>Rule</b></th>
223 </tr>
224 <tr>
225 <td>unsigned</td>
226 <td align="left">A 32-bit unsigned integer that always occupies four
227 consecutive bytes. The unsigned integer is encoded using LSB first
228 ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the
229 byte with the lowest file offset (little endian).</td>
230 </tr><tr>
231 <td>uint_vbr</td>
232 <td align="left">A 32-bit unsigned integer that occupies from one to five
233 bytes using variable bit rate encoding.</td>
234 </tr><tr>
235 <td>uint64_vbr</td>
236 <td align="left">A 64-bit unsigned integer that occupies from one to ten
237 bytes using variable bit rate encoding.</td>
238 </tr><tr>
239 <td>int64_vbr</td>
240 <td align="left">A 64-bit signed integer that occupies from one to ten
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]241 bytes using the signed variable bit rate encoding.</td>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]242 </tr><tr>
243 <td>char</td>
244 <td align="left">A single unsigned character encoded into one byte</td>
245 </tr><tr>
246 <td>bit</td>
247 <td align="left">A single bit within a byte.</td>
248 </tr><tr>
249 <td>string</td>
250 <td align="left">A uint_vbr indicating the length of the character string
251 immediately followed by the characters of the string. There is no
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]252 terminating null byte in the string.</td>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]253 </tr><tr>
254 <td>data</td>
255 <td align="left">An arbitrarily long segment of data to which no
256 interpretation is implied. This is used for float, double, and constant
257 initializers.</td>
258 </tr>
259</table>
260</div>
261<!-- _______________________________________________________________________ -->
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]262<div class="doc_subsection"><a name="align">Alignment</a> </div>
263<div class="doc_text">
264<p>To support cross-platform differences, the bytecode file is aligned on
265certain boundaries. This means that a small amount of padding (at most 3 bytes)
266will be added to ensure that the next entry is aligned to a 32-bit boundary.
267</p>
268</div>
269<!-- *********************************************************************** -->
270<div class="doc_section"> <a name="details">Detailed Layout</a> </div>
271<!-- *********************************************************************** -->
272<div class="doc_text">
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]273<p>This section provides the detailed layout of the LLVM bytecode file format.
274bit and byte level specifics.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]275</div>
276<!-- _______________________________________________________________________ -->
277<div class="doc_subsection"><a name="notation">Notation</a></div>
278<div class="doc_text">
279 <p>The descriptions of the bytecode format that follow describe the bit
280 fields in detail. These descriptions are provided in tabular form. Each table
281 has four columns that specify:</p>
282 <ol>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]283 <li><b>Byte(s)</b>: The offset in bytes of the field from the start of
Reid Spencer6f1d6992004-05-23 17:12:45 +0000[diff] [blame]284 its container (block, list, other field).</li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]285 <li><b>Bit(s)</b>: The offset in bits of the field from the start of
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]286 the byte field. Bits are always little endian. That is, bit addresses with
Reid Spencer6f1d6992004-05-23 17:12:45 +0000[diff] [blame]287 smaller values have smaller address (i.e. 2<sup>0</sup> is at bit 0,
288 2<sup>1</sup> at 1, etc.)
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]289 </li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]290 <li><b>Align?</b>: Indicates if this field is aligned to 32 bits or not.
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]291 This indicates where the <em>next</em> field starts, always on a 32 bit
292 boundary.</li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]293 <li><b>Type</b>: The basic type of information contained in the field.</li>
294 <li><b>Description</b>: Describes the contents of the field.</li>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]295 </ol>
296</div>
297<!-- _______________________________________________________________________ -->
298<div class="doc_subsection"><a name="blocktypes">Block Types</a></div>
299<div class="doc_text">
300 <p>The bytecode format encodes the intermediate representation into groups
301 of bytes known as blocks. The blocks are written sequentially to the file in
302 the following order:</p>
303<ol>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]304 <li><a href="#signature">Signature</a>: This contains the file signature
305 (magic number) that identifies the file as LLVM bytecode and the bytecode
306 version number.</li>
307 <li><a href="#module">Module Block</a>: This is the top level block in a
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]308 bytecode file. It contains all the other blocks.</li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]309 <li><a href="#gtypepool">Global Type Pool</a>: This block contains all the
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]310 global (module) level types.</li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]311 <li><a href="#modinfo">Module Info</a>: This block contains the types of the
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]312 global variables and functions in the module as well as the constant
313 initializers for the global variables</li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]314 <li><a href="#constants">Constants</a>: This block contains all the global
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]315 constants except function arguments, global values and constant strings.</li>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]316 <li><a href="#functions">Functions</a>: One function block is written for
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]317 each function in the module. </li>
Tanya Lattner61f1d2b2004-06-21 23:29:40 +0000[diff] [blame]318 <li><a href="#symtab">Symbol Table</a>: The module level symbol table that
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]319 provides names for the various other entries in the file is the final block
320 written.</li>
321</ol>
322</div>
323<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]324<div class="doc_subsection"><a name="signature">Signature Block</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]325<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]326<p>The signature occurs in every LLVM bytecode file and is always first.
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]327It simply provides a few bytes of data to identify the file as being an LLVM
328bytecode file. This block is always four bytes in length and differs from the
329other blocks because there is no identifier and no block length at the start
330of the block. Essentially, this block is just the "magic number" for the file.
331<table class="doc_table_nw" >
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]332 <tr>
333 <th><b>Byte(s)</b></th>
334 <th><b>Bit(s)</b></th>
335 <th><b>Align?</b></th>
Reid Spencer939290f2004-05-22 05:56:41 +0000[diff] [blame]336 <th><b>Type</b></th>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]337 <th align="left"><b>Field Description</b></th>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]338 </tr><tr>
339 <td>00</td><td>-</td><td>No</td><td>char</td>
Reid Spencer939290f2004-05-22 05:56:41 +0000[diff] [blame]340 <td align="left">Constant "l" (0x6C)</td>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]341 </tr><tr>
342 <td>01</td><td>-</td><td>No</td><td>char</td>
Reid Spencer939290f2004-05-22 05:56:41 +0000[diff] [blame]343 <td align="left">Constant "l" (0x6C)</td>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]344 </tr><tr>
345 <td>02</td><td>-</td><td>No</td><td>char</td>
Reid Spencer939290f2004-05-22 05:56:41 +0000[diff] [blame]346 <td align="left">Constant "v" (0x76)</td>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]347 </tr><tr>
348 <td>03</td><td>-</td><td>No</td><td>char</td>
Reid Spencer939290f2004-05-22 05:56:41 +0000[diff] [blame]349 <td align="left">Constant "m" (0x6D)</td>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]350 </tr>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]351</table>
352</div>
353<!-- _______________________________________________________________________ -->
354<div class="doc_subsection"><a name="module">Module Block</a> </div>
355<div class="doc_text">
356<p>The module block contains a small pre-amble and all the other blocks in
357the file. Of particular note, the bytecode format number is simply a 28-bit
358monotonically increase integer that identifiers the version of the bytecode
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]359format (which is not directly related to the LLVM release number). The
360bytecode versions defined so far are (note that this document only describes
361the latest version): </p>
362
363<ul>
364<li>#0: LLVM 1.0 &amp; 1.1</li>
365<li>#1: LLVM 1.2</li>
366<li>#2: LLVM 1.3</li>
367</ul>
368
369<p>The table below shows the format of the module block header. It is defined
370by blocks described in other sections.</p>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]371<table class="doc_table_nw" >
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]372 <tr>
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]373 <th><b>Byte(s)</b></th>
374 <th><b>Bit(s)</b></th>
375 <th><b>Align?</b></th>
376 <th><b>Type</b></th>
377 <th align="left"><b>Field Description</b></th>
378 </tr><tr>
379 <td>04-07</td><td>-</td><td>No</td><td>unsigned</td>
380 <td align="left">Module Identifier (0x01)</td>
381 </tr><tr>
382 <td>08-11</td><td>-</td><td>No</td><td>unsigned</td>
383 <td align="left">Size of the module block in bytes</td>
384 </tr><tr>
385 <td>12-15</td><td>00</td><td>Yes</td><td>uint32_vbr</td>
386 <td align="left">Format Information</td>
387 </tr><tr>
388 <td>''</td><td>0</td><td>-</td><td>bit</td>
389 <td align="left">Big Endian?</td>
390 </tr><tr>
391 <td>''</td><td>1</td><td>-</td><td>bit</td>
392 <td align="left">Pointers Are 64-bit?</td>
393 </tr><tr>
394 <td>''</td><td>2</td><td>-</td><td>bit</td>
395 <td align="left">Has No Endianess?</td>
396 </tr><tr>
397 <td>''</td><td>3</td><td>-</td><td>bit</td>
398 <td align="left">Has No Pointer Size?</td>
399 </tr><tr>
400 <td>''</td><td>4-31</td><td>-</td><td>bit</td>
401 <td align="left">Bytecode Format Version</td>
402 </tr><tr>
403 <td>16-end</td><td>-</td><td>-</td><td>blocks</td>
404 <td align="left">The remaining bytes in the block consist
405 solely of other block types in sequence.</td>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]406 </tr>
407</table>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]408
409<p>Note that we plan to eventually expand the target description capabilities
410of bytecode files to <a href="http://llvm.cs.uiuc.edu/PR263">target
411triples</a>.</p>
412
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]413</div>
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]414
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]415<!-- _______________________________________________________________________ -->
416<div class="doc_subsection"><a name="gtypepool">Global Type Pool</a> </div>
417<div class="doc_text">
Chris Lattner2b905652004-05-24 05:35:17 +0000[diff] [blame]418<p>The global type pool consists of type definitions. Their order of appearance
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]419in the file determines their slot number (0 based). Slot numbers are used to
420replace pointers in the intermediate representation. Each slot number uniquely
421identifies one entry in a type plane (a collection of values of the same type).
422Since all values have types and are associated with the order in which the type
423pool is written, the global type pool <em>must</em> be written as the first
424block of a module. If it is not, attempts to read the file will fail because
425both forward and backward type resolution will not be possible.</p>
426<p>The type pool is simply a list of types definitions, as shown in the table
427below.</p>
428<table class="doc_table_nw" >
429 <tr>
430 <th><b>Byte(s)</b></th>
431 <th><b>Bit(s)</b></th>
432 <th><b>Align?</b></th>
433 <th><b>Type</b></th>
434 <th align="left"><b>Field Description</b></th>
435 </tr><tr>
436 <td>00-03</td><td>-</td><td>No</td><td>unsigned</td>
437 <td align="left">Type Pool Identifier (0x13)</td>
438 </tr><tr>
439 <td>04-07</td><td>-</td><td>No</td><td>unsigned</td>
440 <td align="left">Size in bytes of the symbol table block.</td>
441 </tr><tr>
442 <td>08-11<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
443 <td align="left">Number of entries in type plane</td>
444 </tr><tr>
445 <td>12-15<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
446 <td align="left">Type plane index for following entries</td>
447 </tr><tr>
448 <td>16-end<sup>1,2</sup></td><td>-</td><td>No</td><td>type</td>
449 <td align="left">Each of the type definitions.</td>
450 </tr><tr>
451 <td align="left" colspan="5"><sup>1</sup>Maximum length shown,
452 may be smaller<br><sup>2</sup>Repeated field.
453 </tr>
454</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]455</div>
456<!-- _______________________________________________________________________ -->
457<div class="doc_subsection"><a name="modinfo">Module Info</a> </div>
458<div class="doc_text">
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]459 <p>To be determined.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]460</div>
461<!-- _______________________________________________________________________ -->
462<div class="doc_subsection"><a name="constants">Constants</a> </div>
463<div class="doc_text">
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]464 <p>To be determined.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]465</div>
466<!-- _______________________________________________________________________ -->
467<div class="doc_subsection"><a name="functions">Functions</a> </div>
468<div class="doc_text">
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]469 <p>To be determined.</p>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]470</div>
471<!-- _______________________________________________________________________ -->
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]472<div class="doc_subsection"><a name="symtab">Symbol Table</a> </div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]473<div class="doc_text">
Reid Spencerb39021b2004-05-23 17:05:09 +0000[diff] [blame]474<p>A symbol table can be put out in conjunction with a module or a function.
475A symbol table is a list of type planes. Each type plane starts with the number
476of entries in the plane and the type plane's slot number (so the type can be
477looked up in the global type pool). For each entry in a type plane, the slot
478number of the value and the name associated with that value are written. The
479format is given in the table below. </p>
480<table class="doc_table_nw" >
481 <tr>
482 <th><b>Byte(s)</b></th>
483 <th><b>Bit(s)</b></th>
484 <th><b>Align?</b></th>
485 <th><b>Type</b></th>
486 <th align="left"><b>Field Description</b></th>
487 </tr><tr>
488 <td>00-03</td><td>-</td><td>No</td><td>unsigned</td>
489 <td align="left">Symbol Table Identifier (0x13)</td>
490 </tr><tr>
491 <td>04-07</td><td>-</td><td>No</td><td>unsigned</td>
492 <td align="left">Size in bytes of the symbol table block.</td>
493 </tr><tr>
494 <td>08-11<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
495 <td align="left">Number of entries in type plane</td>
496 </tr><tr>
497 <td>12-15<sup>1</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
498 <td align="left">Type plane index for following entries</td>
499 </tr><tr>
500 <td>16-19<sup>1,2</sup></td><td>-</td><td>No</td><td>uint32_vbr</td>
501 <td align="left">Slot number of a value.</td>
502 </tr><tr>
503 <td>variable<sup>1,2</sup></td><td>-</td><td>No</td><td>string</td>
504 <td align="left">Name of the value in the symbol table.</td>
505 </tr>
506 <tr>
507 <td align="left" colspan="5"><sup>1</sup>Maximum length shown,
508 may be smaller<br><sup>2</sup>Repeated field.
509 </tr>
510</table>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]511</div>
Reid Spencer7c76d332004-06-08 07:41:41 +0000[diff] [blame]512<!-- *********************************************************************** -->
513<div class="doc_section"> <a name="versiondiffs">Version Differences</a> </div>
514<!-- *********************************************************************** -->
515<div class="doc_text">
516<p>This section describes the differences in the Bytecode Format across LLVM
517versions. The versions are listed in reverse order because it assumes the
518current version is as documented in the previous sections. Each section here
519describes the differences between that version and the one that <i>follows</i>
520</p>
521</div>
522<!-- _______________________________________________________________________ -->
523<div class="doc_subsection">
524<a name="vers12">Version 1.2 Differences From 1.3</a></div>
525<div class="doc_text">
526<p>TBD: How version 1.2 differs from version 1.3</p>
527</div>
528
529<!-- _______________________________________________________________________ -->
530<div class="doc_subsection">
531<a name="vers11">Version 1.1 Differences From 1.2 </a></div>
532<div class="doc_text">
533<p>TBD: How version 1.1 differs from version 1.2</p>
534</div>
535
536<!-- _______________________________________________________________________ -->
537<div class="doc_subsection">
538<a name="vers11">Version 1.0 Differences From 1.1</a></div>
539<div class="doc_text">
540<p>TBD: How version 1.0 differs from version 1.1</p>
541</div>
Reid Spencer50026612004-05-22 02:28:36 +0000[diff] [blame]542
543<!-- *********************************************************************** -->
544<hr>
545<address>
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550
551 <a href="mailto:rspencer@x10sys.com">Reid Spencer</a> and
552 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
553 <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a><br>
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