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An update with corrections to content as well as using a regex style
notation that Chris' suggested to make the specification more compact and succinct. Added a section to Describe the notation, made the VBR description its own section, and otherwise generally cleaned things up. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14668 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer
parent
c964715a76
commit
82c4671f86
@ -22,6 +22,7 @@
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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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@ -57,11 +58,15 @@
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<div class="doc_section"> <a name="abstract">Abstract </a></div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This document describes the LLVM bytecode file format as of version 1.3.
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It specifies the binary encoding rules of the bytecode file format
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so that equivalent systems can encode bytecode files correctly. The LLVM
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bytecode representation is used to store the intermediate representation on
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disk in compacted form.
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<p>This document describes the LLVM bytecode file format. It specifies the
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binary encoding rules of the bytecode file format so that equivalent systems
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can encode bytecode files correctly. The LLVM bytecode representation is
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used to store the intermediate representation on disk in compacted form.</p>
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<p>The LLVM bytecode format may change in the future, but LLVM will always be
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backwards compatible with older formats. This document will only describe
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the most current version of the bytecode format. See
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<a href="#versiondiffs">Version Differences</a> for the details on how the
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current version is different from previous versions.</p>
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</p>
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</div>
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@ -69,28 +74,26 @@ disk in compacted form.
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<div class="doc_section"> <a name="concepts">Concepts</a> </div>
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<!-- *********************************************************************** -->
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<div class="doc_text">
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<p>This section describes the general concepts of the bytecode file format
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without getting into bit and byte level specifics. Note that the LLVM bytecode
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format may change in the future, but will always be backwards compatible with
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older formats. This document only describes the most current version of the
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bytecode format.</p>
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<p>This section describes the general concepts of the bytecode file format
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without getting into specific layout details. It is recommended that you read
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this section thoroughly before interpreting the detailed descriptions.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="blocks">Blocks</a> </div>
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<div class="doc_text">
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<p>LLVM bytecode files consist simply of a sequence of blocks of bytes.
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Each block begins with an header of two unsigned integers. The first value
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identifies the type of block and the second value provides the size of the
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block in bytes. The block identifier is used because it is possible for entire
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blocks to be omitted from the file if they are empty. The block identifier helps
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the reader determine which kind of block is next in the file. Note that blocks
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can be nested within other blocks.</p>
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<p> All blocks are variable length, and the block header specifies the size of
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the block. All blocks begin on a byte index that is aligned to an even 32-bit
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boundary. That is, the first block is 32-bit aligned because it starts at offset
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0. Each block is padded with zero fill bytes to ensure that the next block also
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starts on a 32-bit boundary.</p>
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<p>LLVM bytecode files consist simply of a sequence of blocks of bytes using
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a binary encoding Each block begins with an header of two unsigned integers.
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The first value identifies the type of block and the second value provides
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the size of the block in bytes. The block identifier is used because it is
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possible for entire blocks to be omitted from the file if they are empty.
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The block identifier helps the reader determine which kind of block is next
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in the file. Note that blocks can be nested within other blocks.</p>
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<p> All blocks are variable length, and the block header specifies the size
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of the block. All blocks begin on a byte index that is aligned to an even
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32-bit boundary. That is, the first block is 32-bit aligned because it
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starts at offset 0. Each block is padded with zero fill bytes to ensure that
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the next block also starts on a 32-bit boundary.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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@ -99,16 +102,9 @@ starts on a 32-bit boundary.</p>
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<p>LLVM Bytecode blocks often contain lists of things of a similar type. For
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example, a function contains a list of instructions and a function type
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contains a list of argument types. There are two basic types of lists:
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length lists, and null terminated lists, as described here:</p>
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<ul>
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<li><b>Length Lists</b>. Length lists are simply preceded by the number
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of items in the list. The bytecode reader will read the count first and
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then iterate that many times to read in the list contents.</li>
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<li><b>Null Terminated Lists</b>. For some lists, the number of elements
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in the list is not readily available at the time of writing the bytecode.
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In these cases, the list is terminated by some null value. What constitutes
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a null value differs, but it almost always boils down to a zero value.</li>
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</ul>
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length lists (<a href="#llist">llist</a>), and null terminated lists
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(<a href="#zlist">zlist</a>), as described below in the
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<a href="#encoding">Encoding Primitives</a>.</p>
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</div>
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<!-- _______________________________________________________________________ -->
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@ -136,11 +132,8 @@ 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="encoding">Encoding Primitives</a> </div>
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<div class="doc_subsection"><a name="vbr">Variable Bit-Rate Encoding</a> </div>
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<div class="doc_text">
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<p>Each field that can be put out is encoded into the file using a small set
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of primitives. The rules for these primitives are described below.</p>
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<h3>Variable Bit Rate Encoding</h3>
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<p>Most of the values written to LLVM bytecode files are small integers. To
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minimize the number of bytes written for these quantities, an encoding
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scheme similar to UTF-8 is used to write integer data. The scheme is known as
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@ -177,52 +170,74 @@ with the sign bit as the low order bit instead of the high order bit. This
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allows small negative quantities to be encoded efficiently. For example, -3
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is encoded as "((3 << 1) | 1)" and 3 is encoded as "(3 << 1) |
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0)", emitted with the standard vbr encoding above.</p>
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</div>
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<p>The table below defines the encoding rules for type names used in the
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descriptions of blocks and fields in the next section. Any type name with
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the suffix <em>_vbr</em> indicate a quantity that is encoded using
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variable bit rate encoding as described above.</p>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="encoding">Encoding Primitives</a> </div>
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<div class="doc_text">
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<p>Each field in the bytecode format is encoded into the file using a small
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set of primitive formats. The table below defines the encoding rules for the
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various primitives used and gives them each a type name. The type names used
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in the descriptions of blocks and fields in the <a href="#details">Detailed
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Layout</a>next section. Any type name with the suffix <em>_vbr</em> indicates
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a quantity that is encoded using variable bit rate encoding as described
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above.</p>
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<table class="doc_table" >
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Rule</b></th>
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</tr>
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<tr>
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<td><a name="unsigned">unsigned</a></td>
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<td><a name="unsigned"><b>unsigned</b></a></td>
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<td class="td_left">A 32-bit unsigned integer that always occupies four
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consecutive bytes. The unsigned integer is encoded using LSB first
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ordering. That is bits 2<sup>0</sup> through 2<sup>7</sup> are in the
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byte with the lowest file offset (little endian).</td>
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</tr><tr>
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<td><a name="uint32_vbr">uint32_vbr</a></td>
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<td><a name="uint32_vbr"><b>uint32_vbr</b></a></td>
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<td class="td_left">A 32-bit unsigned integer that occupies from one to five
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bytes using variable bit rate encoding.</td>
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</tr><tr>
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<td><a name="uint64_vbr">uint64_vbr</a></td>
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<td><a name="uint64_vbr"><b>uint64_vbr</b></a></td>
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<td class="td_left">A 64-bit unsigned integer that occupies from one to ten
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bytes using variable bit rate encoding.</td>
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</tr><tr>
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<td><a name="int64_vbr">int64_vbr</a></td>
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<td><a name="int64_vbr"><b>int64_vbr</b></a></td>
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<td class="td_left">A 64-bit signed integer that occupies from one to ten
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bytes using the signed variable bit rate encoding.</td>
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</tr><tr>
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<td><a name="char">char</a></td>
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<td><a name="char"><b>char</b></a></td>
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<td class="td_left">A single unsigned character encoded into one byte</td>
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</tr><tr>
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<td><a name="bit">bit</a></td>
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<td class="td_left">A single bit within some larger integer field.</td>
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<td><a name="bit"><b>bit(n-m)</b></a></td>
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<td class="td_left">A set of bit within some larger integer field. The
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values of <code>n</code> and <code>m</code> specify the inclusive range
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of bits that define the subfield. The value for <code>m</code> may be
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omitted if its the same as <code>n</code>.</td>
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</tr><tr>
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<td><a name="string">string</a></td>
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<td><a name="string"><b>string</b></a></td>
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<td class="td_left">A uint32_vbr indicating the type of the constant string
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which also includes its length, immediately followed by the characters of
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the string. There is no terminating null byte in the string.</td>
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</tr><tr>
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<td><a name="data">data</a></td>
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<td><a name="data"><b>data</b></a></td>
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<td class="td_left">An arbitrarily long segment of data to which no
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interpretation is implied. This is used for float, double, and constant
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initializers.</td>
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</tr><tr>
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<td><a name="block">block</a></td>
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<td><a name="llist"><b>llist(x)</b></a></td>
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<td class="td_left">A length list of x. This means the list is encoded as
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an <a href="#uint32_vbr">uint32_vbr</a> providing the length of the list,
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followed by a sequence of that many "x" items. This implies that the reader
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should iterate the number of times provided by the length.</td>
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</tr><tr>
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<td><a name="zlist"><b>zlist(x)</b></a></td>
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<td class="td_left">A zero-terminated list of x. This means the list is encoded
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as a sequence of an indeterminate number of "x" items, followed by an
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<a href="#uint32_vbr">uint32_vbr</a> terminating value. This implies that none
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of the "x" items can have a zero value (or else the list terminates).</td>
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</tr><tr>
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<td><a name="block"><b>block</b></a></td>
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<td class="td_left">A block of data that is logically related. A block
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begins with an <a href="#unsigned">unsigned</a> that provides the block
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identifier (constant value) and an <a href="#unsigned">unsigned</a> that
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@ -232,6 +247,56 @@ variable bit rate encoding as described above.</p>
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</table>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="notation">Field Notation</a> </div>
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<div class="doc_text">
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<p>In the detailed block and field descriptions that follow, a regex like
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notation is used to describe optional and repeated fields. A very limited
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subset of regex is used to describe these, as given in the following table:
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</p>
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<table class="doc_table" >
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<tr>
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<th><b>Character</b></th>
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<th class="td_left"><b>Meaning</b></th>
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</tr><tr>
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<td><b><code>?</code></b></td>
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<td class="td_left">The question mark indicates 0 or 1 occurrences of
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the thing preceding it.</td>
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</tr><tr>
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<td><b><code>*</code></b></td>
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<td class="td_left">The asterisk indicates 0 or more occurrences of the
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thing preceding it.</td>
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</tr><tr>
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<td><b><code>+</code></b></td>
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<td class="td_left">The plus sign indicates 1 or more occurrences of the
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thing preceding it.</td>
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</tr><tr>
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<td><b><code>()</code></b></td>
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<td class="td_left">Parentheses are used for grouping.</td>
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</tr><tr>
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<td><b><code>,</code></b></td>
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<td class="td_left">The comma separates sequential fields.</td>
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</tr>
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</table>
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<p>So, for example, consider the following specifications:</p>
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<div class="doc_code">
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<ol>
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<li><code>string?</code></li>
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<li><code>(uint32_vbr,uin32_vbr)+</code></li>
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<li><code>(unsigned?,uint32_vbr)*</code></li>
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<li><code>(llist(unsigned))?</code></li>
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</ol>
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</div>
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<p>with the following interpretations:</p>
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<ol>
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<li>An optional string. Matches either nothing or a single string</li>
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<li>One or more pairs of uint32_vbr.</li>
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<li>Zero or more occurrences of either an unsigned followed by a uint32_vbr
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or just a uint32_vbr.</li>
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<li>An optional length list of unsigned values.</li>
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</ol>
|
||||
</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="slots">Slots</a> </div>
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<div class="doc_text">
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@ -240,10 +305,10 @@ Values. Since the bytecode file is a <em>direct</em> representation of LLVM's
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intermediate representation, there is a need to represent pointers in the file.
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Slots are used for this purpose. For example, if one has the following assembly:
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</p>
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<div class="doc_code">
|
||||
<div class="doc_code"><code>
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%MyType = type { int, sbyte }<br>
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%MyVar = external global %MyType
|
||||
</div>
|
||||
</code></div>
|
||||
<p>there are two definitions. The definition of <tt>%MyVar</tt> uses
|
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<tt>%MyType</tt>. In the C++ IR this linkage between <tt>%MyVar</tt> and
|
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<tt>%MyType</tt> is
|
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@ -276,7 +341,7 @@ This is exactly what the compaction table does.</p>
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<div class="doc_section"> <a name="general">General Structure</a> </div>
|
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<!-- *********************************************************************** -->
|
||||
<div class="doc_text">
|
||||
<p>This section provides the general structur of the LLVM bytecode file
|
||||
<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
|
||||
@ -321,7 +386,7 @@ This is exactly what the compaction table does.</p>
|
||||
except function arguments, global values and constant strings.</td>
|
||||
</tr>
|
||||
<tr><td>0x11</td><td>Module</td><td>Yes</td><td>Yes</td><td>1</td>
|
||||
<td class="td_left"> <a href="#functiondefs">Function Definitions</a></td>
|
||||
<td class="td_left"> <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>
|
||||
@ -356,8 +421,7 @@ This is exactly what the compaction table does.</p>
|
||||
functions mostly).</td>
|
||||
</tr>
|
||||
</table>
|
||||
<p>Use the links in the table or see <a href="#blocktypes">Block Types</a> for
|
||||
details about the contents of each of the block types.</p>
|
||||
<p>Use the links in the table for details about the contents of each of the block types.</p>
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
@ -427,7 +491,7 @@ sections.</p>
|
||||
<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><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>
|
||||
@ -443,24 +507,23 @@ sections.</p>
|
||||
integer as shown in the following table.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td>0</td><td>bit</td>
|
||||
<td class="td_left">Big Endian?</td>
|
||||
<td><a href="#bit">bit(0)</a></td>
|
||||
<td class="td_left">Target is big endian?</td>
|
||||
</tr><tr>
|
||||
<td>1</td><td>bit</td>
|
||||
<td class="td_left">Pointers Are 64-bit?</td>
|
||||
<td><a href="#bit">bit(1)</a></td>
|
||||
<td class="td_left">On target pointers are 64-bit?</td>
|
||||
</tr><tr>
|
||||
<td>2</td><td>bit</td>
|
||||
<td class="td_left">Has No Endianess?</td>
|
||||
<td><a href="#bit">bit(2)</a></td>
|
||||
<td class="td_left">Target has no endianess?</td>
|
||||
</tr><tr>
|
||||
<td>3</td><td>bit</td>
|
||||
<td class="td_left">Has No Pointer Size?</td>
|
||||
<td><a href="#bit">bit(3)</a></td>
|
||||
<td class="td_left">Target has no pointer size?</td>
|
||||
</tr><tr>
|
||||
<td>4-31</td><td>bit</td>
|
||||
<td class="td_left">Bytecode Format Version</td>
|
||||
<td><a href="#bit">bit(4-31)</a></td>
|
||||
<td class="td_left">Bytecode format version</td>
|
||||
</tr>
|
||||
</table>
|
||||
<p>
|
||||
@ -503,24 +566,16 @@ below.</p>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size in bytes of the type pool block.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Number of type definitions that follow in the next
|
||||
field.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#type">type</a></td>
|
||||
<td class="td_left">Each of the type definitions (see below)<sup>1</sup></td>
|
||||
<td><a href="#llist">llist</a>(<a href="#type">type</a>)</td>
|
||||
<td class="td_left">A length list of type definitions.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>Repeated field.</li>
|
||||
</ol>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
|
||||
<div class="doc_text">
|
||||
<p>Types in the type pool are defined using a different format for each
|
||||
basic type of type as given in the following sections.</p>
|
||||
<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>
|
||||
@ -528,14 +583,29 @@ basic type of type as given in the following sections.</p>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Type ID For The Primitive (1-11)<sup>1</sup></td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type ID for the primitive types (values 1 to 11)
|
||||
<sup>1</sup></td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>See the definition of Type::TypeID in Type.h for the numeric equivalents
|
||||
of the primitive type ids.</li>
|
||||
<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>
|
||||
@ -543,60 +613,45 @@ Notes:
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type ID for function types (13)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Slot number of function's return type.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">The number of arguments in the function.</td>
|
||||
<td><a href="#llist">llist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
|
||||
<td class="td_left">Slot number of each argument's type.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of each argument's type.<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Value 0 if this is a varargs function.<sup>2</sup></td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a>?</td>
|
||||
<td class="td_left">Value 0 if this is a varargs function, missing otherwise.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>Repeated field.</li>
|
||||
<li>Optional field.</li>
|
||||
</ol>
|
||||
<h3>Structure Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type ID for structure types (14)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Slot number of each of the element's fields.<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td class="td_left">Null Terminator (VoidTy type id)</td>
|
||||
<td><a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
|
||||
<td class="td_left">Slot number of each of the element's fields.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>Repeatable field.</li>
|
||||
</ol>
|
||||
<h3>Array Types</h3>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type ID for Array Types (15)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Slot number of array's element type.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The number of elements in the array.</td>
|
||||
</tr>
|
||||
</table>
|
||||
@ -606,10 +661,10 @@ Notes:
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type ID For Pointer Types (16)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Slot number of pointer's element type.</td>
|
||||
</tr>
|
||||
</table>
|
||||
@ -619,7 +674,7 @@ Notes:
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type ID For Opaque Types (17)</td>
|
||||
</tr>
|
||||
</table>
|
||||
@ -641,70 +696,60 @@ Notes:
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size in bytes of the module global info block.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#globalvar">globalvar</a></td>
|
||||
<td class="td_left">Definition of the global variable (see below).
|
||||
<sup>1</sup>
|
||||
</td>
|
||||
<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="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Slot number of the global variable's constant
|
||||
initializer.<sup>1,2</sup>
|
||||
</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Zero. This terminates the list of global variables.
|
||||
</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type slot number of a function defined in this
|
||||
bytecode file.<sup>3</sup>
|
||||
</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Zero. This terminates the list of function
|
||||
declarations.
|
||||
<td><a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>)</td>
|
||||
<td class="td_left">A zero terminated list of function types occuring in
|
||||
the module.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:<ol>
|
||||
<li>Both these fields are repeatable but in pairs.</li>
|
||||
<li>Optional field.</li>
|
||||
<li>Repeatable field.</li>
|
||||
</ol>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
|
||||
</div>
|
||||
<div class="doc_text">
|
||||
<p>Global variables are written using a single
|
||||
<a href="#uint32_vbr">uint32_vbr</a> that encodes information about the global
|
||||
variable. The table below provides the bit layout of the value written for
|
||||
each global variable.</p>
|
||||
<p>Global variables are written using an <a href="#uint32_vbr">uint32_vbr</a>
|
||||
that encodes information about the global variable and a list of the constant
|
||||
initializers for the global var, if any.</p>
|
||||
<p>The table below provides the bit layout of the first
|
||||
<a href="#uint32_vbr">uint32_vbr</a> that describes the global variable.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Bit(s)</b></th>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td>0</td><td>bit</td>
|
||||
<td><a href="#bit">bit(0)</a></td>
|
||||
<td class="td_left">Is constant?</td>
|
||||
</tr><tr>
|
||||
<td>1</td><td>bit</td>
|
||||
<td class="td_left">Has initializer?<sup>1</sup></td>
|
||||
<td><a href="#bit">bit(1)</a></td>
|
||||
<td class="td_left">Has initializer? Note that this bit determines whether
|
||||
the constant initializer field (described below) follows.</li>
|
||||
</tr><tr>
|
||||
<td>2-4</td><td>enumeration</td>
|
||||
<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>5-31</td><td>type slot</td>
|
||||
<td><a href="#bit">bit(5-31)</a></td>
|
||||
<td class="td_left">Slot number of type for the global variable.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>This bit determines whether the constant initializer field follows
|
||||
immediately after this field</li>
|
||||
</ol>
|
||||
<p>The table below provides the format of the constant initializers for the
|
||||
global variable field, if it has one.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Description</b></th>
|
||||
</tr><tr>
|
||||
<td>(<a href="#zlist">zlist</a>(<a href="#uint32_vbr">uint32_vbr</a>))?
|
||||
</a>
|
||||
</td>
|
||||
<td class="td_left">An optional zero-terminated list of slot numbers of
|
||||
the global variable's constant initializer.</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
@ -714,7 +759,7 @@ Notes:
|
||||
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 the follow,
|
||||
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>
|
||||
@ -725,6 +770,9 @@ Notes:
|
||||
</tr><tr>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Constant pool identifier (0x12)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size in bytes of the constant pool block.</td>
|
||||
</tr>
|
||||
</table>
|
||||
<p><b>Module Constant Pool Preamble (constant strings)</b></p>
|
||||
@ -738,19 +786,17 @@ Notes:
|
||||
</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.
|
||||
containing the constant strings. This is needed to identify it
|
||||
uniquely from other constant planes that follow.
|
||||
</td>
|
||||
</tr><tr>
|
||||
<td><a href="#string">string</a></td>
|
||||
<td class="td_left">Slot number of the constant string's type which
|
||||
includes the length of the string.<sup>1</sup>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
||||
<td class="td_left">Slot number of the constant string's type. Note
|
||||
that the constant string's type implicitly defines the length of
|
||||
the string.
|
||||
</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>Repeated field.</li>
|
||||
</ol>
|
||||
<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
|
||||
@ -767,7 +813,7 @@ Notes:
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Type slot number of this plane.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#constant">constant</a></td>
|
||||
<td><a href="#constant">constant</a>+</td>
|
||||
<td class="td_left">The definition of a constant (see below).</td>
|
||||
</tr>
|
||||
</table>
|
||||
@ -825,33 +871,40 @@ Notes:
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="functiondefs">Function Definition</a></div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
<p>Function definitions contain the linkage, constant pool or compaction
|
||||
table, instruction list, and symbol table for a function. The following table
|
||||
shows the structure of a function definition.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Function definition block identifier (0x11)</td>
|
||||
</tr><tr>
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size in bytes of the function definition block.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The linkage type of the function: 0=External, 1=Weak,
|
||||
2=Appending, 3=Internal, 4=LinkOnce<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td><a href="#constantpool">constant pool</a></td>
|
||||
<td class="td_left">The constant pool block for this function.
|
||||
<sup>2</sup>
|
||||
</td>
|
||||
<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="#compactiontable">compaction table</a></td>
|
||||
<td class="td_left">The compaction table block for the function.
|
||||
<sup>2</sup>
|
||||
</td>
|
||||
<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="#instructionlist">instruction list</a></td>
|
||||
<td class="td_left">The list of instructions in the function.</td>
|
||||
<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="#symboltable">symbol table</a></td>
|
||||
<td class="td_left">The function's slot table containing only those
|
||||
symbols pertinent to the function (mostly block labels).
|
||||
</td>
|
||||
<td><a href="#block">block</a></td>
|
||||
<td class="td_left">The function's <a href="#symboltable">symbol table</a>
|
||||
containing only those symbols pertinent to the function (mostly
|
||||
block labels).</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:<ol>
|
||||
@ -869,13 +922,14 @@ Notes:
|
||||
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 compresses instruction format reserves only six bits for
|
||||
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. Compaction tables have the
|
||||
format shown in the table below.</p>
|
||||
numbers to smaller values used by a function. Functions will contain either
|
||||
a function-specific constant pool <em>or</em> a compaction table but not
|
||||
both. Compaction tables have the format shown in the table below.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
@ -884,26 +938,23 @@ Notes:
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The number of types that follow</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
||||
<td class="td_left">The slot number in the global type plane of the
|
||||
type that will be referenced in the function with the index of
|
||||
this entry in the compaction table.<sup>1</sup></td>
|
||||
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.<sup>2</sup></td>
|
||||
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><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<sup>1</sup></td>
|
||||
the compaction table</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:<ol>
|
||||
<li>Repeated field.</li>
|
||||
<li>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.
|
||||
</ol>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
@ -935,15 +986,11 @@ Notes:
|
||||
<td><a href="#unsigned">unsigned</a></td>
|
||||
<td class="td_left">Size in bytes of the instruction list.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#instruction">instruction</a></td>
|
||||
<td class="td_left">An instruction.<sup>1</sup></td>
|
||||
<td><a href="#instruction">instruction</a>+</td>
|
||||
<td class="td_left">An instruction. Instructions have a variety of formats.
|
||||
See <a href="#instruction">Instructions</a> for details.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>A repeated field with a variety of formats. See
|
||||
<a href="#instruction">Instructions</a> for details.</li>
|
||||
</ol>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
@ -975,13 +1022,12 @@ Notes:
|
||||
<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 for the operand(s).
|
||||
<sup>1,2</sup></td>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a>+</td>
|
||||
<td class="td_left">The slot number of the value(s) for the operand(s).
|
||||
<sup>1</sup></td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:<ol>
|
||||
<li>Repeatable field (limit given by previous field).</li>
|
||||
<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
|
||||
@ -1003,7 +1049,7 @@ Notes:
|
||||
</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 si 63.</td>
|
||||
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
|
||||
@ -1031,7 +1077,7 @@ Notes:
|
||||
</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 si 63.</td>
|
||||
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
|
||||
@ -1062,7 +1108,7 @@ Notes:
|
||||
</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 si 63.</td>
|
||||
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
|
||||
@ -1106,19 +1152,14 @@ format is given in the table below. </p>
|
||||
<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.
|
||||
<sup>1</sup></td>
|
||||
<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><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.<sup>1</sup></td>
|
||||
for all values of the same type.</td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>Repeated field.</li>
|
||||
</ol>
|
||||
</div>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
@ -1138,8 +1179,8 @@ Notes:
|
||||
<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 (repeated).</td>
|
||||
<td><a href="#symtab_entry">symtab_entry</a>+</td>
|
||||
<td class="td_left">The symbol table entries for this plane.</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
@ -1163,8 +1204,8 @@ Notes:
|
||||
<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 (repeated).</td>
|
||||
<td><a href="#char">char</a>+</td>
|
||||
<td class="td_left">The characters of the name.</td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
|
||||
Loading…
Reference in New Issue
Block a user