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Added sections for Constant Pool, Module Global Info, and Compaction
Tables. Two more sections to go. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14631 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Reid Spencer
parent
1cc070c707
commit
2cc361555b
@ -5,11 +5,11 @@
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<title>LLVM Bytecode File Format</title>
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<link rel="stylesheet" href="llvm.css" type="text/css">
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<style type="text/css">
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TR, TD { border: 2px solid gray; padding: 4pt 4pt 4pt 4pt; }
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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; padding: 4pt 4pt 4pt 4pt; border: 2px solid black;
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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; padding: 4pt 4pt 4pt 4pt; text-align: left; }
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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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@ -161,7 +161,7 @@ also contributes to the value. For the final byte (byte & 0x80) is false
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the value. Consequently 32-bit quantities can take from one to <em>five</em>
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bytes to encode. In general, smaller quantities will encode in fewer bytes,
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as follows:</p>
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<table class="doc_table_nw">
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<table>
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<tr>
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<th>Byte #</th>
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<th>Significant Bits</th>
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@ -222,9 +222,9 @@ variable bit rate encoding as described above.</p>
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<td class="td_left">A single bit within some larger integer field.</td>
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</tr><tr>
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<td><a name="string">string</a></td>
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<td class="td_left">A uint_vbr indicating the length of the character string
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immediately followed by the characters of the string. There is no
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terminating null byte in the string.</td>
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<td class="td_left">A uint_vbr indicating the type of the character 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 class="td_left">An arbitrarily long segment of data to which no
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@ -419,7 +419,7 @@ It simply provides a few bytes of data to identify the file as being an LLVM
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bytecode file. This block is always four bytes in length and differs from the
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other blocks because there is no identifier and no block length at the start
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of the block. Essentially, this block is just the "magic number" for the file.
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<table class="doc_table_nw" >
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
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@ -447,7 +447,7 @@ the file. The table below shows the structure of the module block. Note that it
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only provides the module identifier, size of the module block, and the format
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information. Everything else is contained in other blocks, described in other
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sections.</p>
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<table class="doc_table_nw" >
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
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@ -535,28 +535,29 @@ block of a module. If it is not, attempts to read the file will fail because
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both forward and backward type resolution will not be possible.</p>
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<p>The type pool is simply a list of type definitions, as shown in the table
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below.</p>
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<table class="doc_table_nw" >
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
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</tr><tr>
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<td><a href="#unsigned">unsigned</a></td>
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<td class="td_left">Type Pool Identifier (0x13)</td>
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<td class="td_left">Type Pool Identifier (0x15)</td>
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</tr><tr>
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<td><a href="#unsigned">unsigned</a></td>
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<td class="td_left">Size in bytes of the symbol table block.</td>
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<td class="td_left">Size in bytes of the type pool block.</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Number of entries in type plane</td>
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<td class="td_left">Number of type definitions that follow in the next
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field.</td>
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</tr><tr>
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<td><a href="#type">type</a></td>
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<td class="td_left">Each of the type definitions (see below)<sup>1</sup></td>
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</tr><tr>
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<td class="td_left" colspan="2">
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<sup>1</sup>Repeated field.<br/>
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</td>
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</tr>
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</table>
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Notes:
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<ol>
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<li>Repeated field.</li>
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</ol>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection"><a name="type">Type Definitions</a></div>
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@ -572,13 +573,13 @@ basic type of type as given in the following sections.</p>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</td>
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<td class="td_left">Type ID For The Primitive (1-11)<sup>1</sup></td>
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</tr><tr>
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<td class="td_left" colspan="2">
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<sup>1</sup>See the definition of Type::TypeID in Type.h for the numeric
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equivalents of the primitive type ids.<br/>
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</td>
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</tr>
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</table>
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Notes:
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<ol>
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<li>See the definition of Type::TypeID in Type.h for the numeric equivalents
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of the primitive type ids.</li>
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</ol>
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<h3>Function Types</h3>
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<table>
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<tr>
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@ -599,13 +600,13 @@ basic type of type as given in the following sections.</p>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</td>
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<td class="td_left">Value 0 if this is a varargs function.<sup>2</sup></td>
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</tr><tr>
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<td class="td_left" colspan="2">
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<sup>1</sup>Repeated field.<br/>
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<sup>2</sup>Optional field.
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</td>
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</tr>
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</table>
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Notes:
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<ol>
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<li>Repeated field.</li>
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<li>Optional field.</li>
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</ol>
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<h3>Structure Types</h3>
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<table>
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<tr>
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@ -620,12 +621,12 @@ basic type of type as given in the following sections.</p>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</td>
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<td class="td_left">Null Terminator (VoidTy type id)</td>
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</tr><tr>
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<td class="td_left" colspan="2">
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<sup>1</sup>Repeated field.<br/>
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</td>
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</tr>
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</table>
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Notes:
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<ol>
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<li>Repeatable field.</li>
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</ol>
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<h3>Array Types</h3>
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<table>
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<tr>
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@ -669,12 +670,200 @@ basic type of type as given in the following sections.</p>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="globalinfo">Module Global Info</a> </div>
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<div class="doc_text">
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<p>To be determined.</p>
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<p>The module global info block contains the definitions of all global
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variables including their initializers and the <em>declaration</em> of all
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functions. The format is shown in the table below</p>
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
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</tr><tr>
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<td><a href="#unsigned">unsigned</a></td>
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<td class="td_left">Module global info identifier (0x14)</td>
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</tr><tr>
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<td><a href="#unsigned">unsigned</a></td>
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<td class="td_left">Size in bytes of the module global info block.</td>
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</tr><tr>
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<td><a href="#globalvar">globalvar</a></td>
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<td class="td_left">Definition of the global variable (see below).
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<sup>1</sup>
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</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Slot number of the global variable's constant
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initializer.<sup>1,2</sup>
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</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Zero. This terminates the list of global variables.
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</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Type slot number of a function defined in this
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bytecode file.<sup>3</sup>
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</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Zero. This terminates the list of function
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declarations.
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</tr>
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</table>
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Notes:<ol>
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<li>Both these fields are repeatable but in pairs.</li>
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<li>Optional field.</li>
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<li>Repeatable field.</li>
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</ol>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection"><a name="globalvar">Global Variable Field</a>
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</div>
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<div class="doc_text">
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<p>Global variables are written using a single
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<a href="#uint32_vbr">uint32_vbr</a> that encodes information about the global
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variable. The table below provides the bit layout of the value written for
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each global variable.</p>
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<table>
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<tr>
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<th><b>Bit(s)</b></th>
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<th><b>Type</b></th>
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<th class="td_left"><b>Description</b></th>
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</tr><tr>
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<td>0</td><td>bit</td>
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<td class="td_left">Is constant?</td>
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</tr><tr>
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<td>1</td><td>bit</td>
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<td class="td_left">Has initializer?<sup>1</sup></td>
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</tr><tr>
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<td>2-4</td><td>enumeration</td>
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<td class="td_left">Linkage type: 0=External, 1=Weak, 2=Appending,
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3=Internal, 4=LinkOnce</td>
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</tr><tr>
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<td>5-31</td><td>type slot</td>
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<td class="td_left">Slot number of type for the global variable.</td>
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</tr>
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</table>
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Notes:
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<ol>
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<li>This bit determines whether the constant initializer field follows
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immediately after this field</li>
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</ol>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsection"><a name="constantpool">Constant Pool</a> </div>
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<div class="doc_text">
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<p>To be determined.</p>
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<p>A constant pool defines as set of constant values. There are actually two
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types of constant pool blocks: one for modules and one for functions. For
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modules, the block begins with the constant strings encountered anywhere in
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the module. For functions, the block begins with types only encountered in
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the function. In both cases the header is identical. The tables the follow,
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show the header, module constant pool preamble, function constant pool
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preamble, and the part common to both function and module constant pools.</p>
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<p><b>Common Block Header</b></p>
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
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</tr><tr>
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<td><a href="#unsigned">unsigned</a></td>
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<td class="td_left">Constant pool identifier (0x12)</td>
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</tr>
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</table>
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<p><b>Module Constant Pool Preamble (constant strings)</b></p>
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">The number of constant strings that follow.</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Zero. This identifies the following "plane" as
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containing the constant strings.
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</td>
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</tr><tr>
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<td><a href="#string">string</a></td>
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<td class="td_left">Slot number of the constant string's type which
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includes the length of the string.<sup>1</sup>
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</td>
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</tr>
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</table>
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Notes:
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<ol>
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<li>Repeated field.</li>
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</ol>
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<p><b>Function Constant Pool Preamble (function types)</b></p>
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<p>The structure of the types for functions is identical to the
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<a href="#globaltypes">Global Type Pool</a>. Please refer to that section
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for the details.
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<p><b>Common Part (other constants)</b></p>
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<table>
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<tr>
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<th><b>Type</b></th>
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<th class="td_left"><b>Field Description</b></th>
|
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</tr><tr>
|
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
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<td class="td_left">Number of entries in this type plane.</td>
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</tr><tr>
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<td><a href="#uint32_vbr">uint32_vbr</a></td>
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<td class="td_left">Type slot number of this plane.</td>
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</tr><tr>
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<td><a href="#constant">constant</a></td>
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<td class="td_left">The definition of a constant (see below).</td>
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</tr>
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</table>
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</div>
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<!-- _______________________________________________________________________ -->
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<div class="doc_subsubsection"><a name="constant">Constant Field</a></div>
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<div class="doc_text">
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<p>Constants come in many shapes and flavors. The sections that followe define
|
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the format for each of them. All constants start with a
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<a href="#uint32_vbr">uint32_vbr</a> encoded integer that provides the number
|
||||
of operands for the constant. For primitive, structure, and array constants,
|
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this will always be zero since those types of constants have no operands.
|
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In this case, we have the following field definitions:</p>
|
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<ul>
|
||||
<li><b>Bool</b>. This is written as an <a href="#uint32_vbr">uint32_vbr</a>
|
||||
of value 1U or 0U.</li>
|
||||
<li><b>Signed Integers (sbyte,short,int,long)</b>. These are written as
|
||||
an <a href="#int64_vbr">int64_vbr</a> with the corresponding value.</li>
|
||||
<li><b>Unsigned Integers (ubyte,ushort,uint,ulong)</b>. These are written
|
||||
as an <a href="#uint64_vbr">uint64_vbr</a> with the corresponding value.
|
||||
</li>
|
||||
<li><b>Floating Point</b>. Both the float and double types are written
|
||||
literally in binary format.</li>
|
||||
<li><b>Arrays</b>. Arrays are written simply as a list of
|
||||
<a href="#uint32_vbr">uint32_vbr</a> encoded slot numbers to the constant
|
||||
element values.</li>
|
||||
<li><b>Structures</b>. Structures are written simply as a list of
|
||||
<a href="#uint32_vbr">uint32_vbr</a> encoded slot numbers to the constant
|
||||
field values of the structure.</li>
|
||||
</ul>
|
||||
<p>When the number of operands to the constant is non-zero, we have a
|
||||
constant expression and its field format is provided in the table below.</p>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">Op code of the instruction for the constant
|
||||
expression.</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The slot number of the constant value for an
|
||||
operand.<sup>1</sup></td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The slot number for the type of the constant value
|
||||
for an operand.<sup>1</sup></td>
|
||||
</tr>
|
||||
</table>
|
||||
Notes:<ol>
|
||||
<li>Both these fields are repeatable but only in pairs.</li>
|
||||
</ol>
|
||||
</div>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="functiondefs">Function Definition</a> </div>
|
||||
@ -684,8 +873,59 @@ basic type of type as given in the following sections.</p>
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<div class="doc_subsection"><a name="compactiontable">Compaction Table</a> </div>
|
||||
<div class="doc_text">
|
||||
<p>To be determined.</p>
|
||||
<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 compresses 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>
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Type</b></th>
|
||||
<th class="td_left"><b>Field Description</b></th>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The number of types that follow</td>
|
||||
</tr><tr>
|
||||
<td><a href="#uint32_vbr">uint32_vbr</a></td>
|
||||
<td class="td_left">The slot number in the global type plane of the
|
||||
type that will be referenced in the function with the index of
|
||||
this entry in the compaction table.<sup>1</sup></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>
|
||||
</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<sup>1</sup></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>
|
||||
|
||||
<!-- _______________________________________________________________________ -->
|
||||
<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">
|
||||
@ -700,7 +940,7 @@ of entries in the plane and the type plane's slot number (so the type can be
|
||||
looked up in the global type pool). For each entry in a type plane, the slot
|
||||
number of the value and the name associated with that value are written. The
|
||||
format is given in the table below. </p>
|
||||
<table class="doc_table_nw" >
|
||||
<table>
|
||||
<tr>
|
||||
<th><b>Byte(s)</b></th>
|
||||
<th><b>Bit(s)</b></th>
|
||||
@ -726,11 +966,13 @@ format is given in the table below. </p>
|
||||
<td>variable<sup>1,2</sup></td><td>-</td><td>No</td><td>string</td>
|
||||
<td class="td_left">Name of the value in the symbol table.</td>
|
||||
</tr>
|
||||
<tr>
|
||||
<td class="td_left" colspan="5"><sup>1</sup>Maximum length shown,
|
||||
may be smaller<br><sup>2</sup>Repeated field.
|
||||
</tr>
|
||||
</table>
|
||||
Notes:
|
||||
<ol>
|
||||
<li>Maximum length shown, may be smaller</li>
|
||||
<li>Repeated field.</li>
|
||||
</ol>
|
||||
</div>
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_section"> <a name="versiondiffs">Version Differences</a> </div>
|
||||
|
||||
Loading…
Reference in New Issue
Block a user