| <!DOCTYPE html> |
| |
| <html lang="en" data-content_root="./"> |
| <head> |
| <meta charset="utf-8" /> |
| <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="viewport" content="width=device-width, initial-scale=1" /> |
| |
| <title>Binary Format — WebAssembly Custom Sections</title> |
| <link rel="stylesheet" type="text/css" href="_static/pygments.css?v=fa44fd50" /> |
| <link rel="stylesheet" type="text/css" href="_static/basic.css?v=686e5160" /> |
| <link rel="stylesheet" type="text/css" href="_static/alabaster.css?v=057308f9" /> |
| <script src="_static/documentation_options.js?v=7f41d439"></script> |
| <script src="_static/doctools.js?v=9bcbadda"></script> |
| <script src="_static/sphinx_highlight.js?v=dc90522c"></script> |
| <script>window.MathJax = {"tex": {"maxBuffer": 30720}}</script> |
| <script defer="defer" src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> |
| <link rel="search" title="Search" href="search.html" /> |
| <link rel="next" title="Text Format" href="text.html" /> |
| <link rel="prev" title="Introduction" href="intro.html" /> |
| |
| <link rel="stylesheet" href="_static/custom.css" type="text/css" /> |
| |
| |
| |
| |
| |
| </head><body> |
| <div class="document"> |
| |
| <div class="sphinxsidebar" role="navigation" aria-label="Main"> |
| <div class="sphinxsidebarwrapper"> |
| <p class="logo"><a href="index.html"> |
| <img class="logo" src="_static/webassembly.png" alt="Logo of WebAssembly-Metadata-Code"/> |
| </a></p><h3>Navigation</h3> |
| <ul class="current"> |
| <li class="toctree-l1"><a class="reference internal" href="intro.html">Introduction</a></li> |
| <li class="toctree-l1 current"><a class="current reference internal" href="#">Binary Format</a></li> |
| <li class="toctree-l1"><a class="reference internal" href="text.html">Text Format</a></li> |
| </ul> |
| |
| |
| <hr /> |
| <ul> |
| |
| <li class="toctree-l1"><a href="./_download/WebAssembly-Metadata-Code.pdf">Download as PDF</a></li> |
| |
| </ul> |
| |
| <search id="searchbox" style="display: none" role="search"> |
| <h3 id="searchlabel">Quick search</h3> |
| <div class="searchformwrapper"> |
| <form class="search" action="search.html" method="get"> |
| <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/> |
| <input type="submit" value="Go" /> |
| </form> |
| </div> |
| </search> |
| <script>document.getElementById('searchbox').style.display = "block"</script> |
| </div> |
| </div> |
| <div class="documentwrapper"> |
| <div class="bodywrapper"> |
| |
| |
| <div class="body" role="main"> |
| |
| <section id="binary-format"> |
| <span id="binary"></span><h1>Binary Format<a class="headerlink" href="#binary-format" title="Link to this heading">¶</a></h1> |
| <section id="code-metadata"> |
| <span id="binary-codemetadata"></span><h2>Code Metadata<a class="headerlink" href="#code-metadata" title="Link to this heading">¶</a></h2> |
| <p>A Code Metadata item is a piece of information logically attached to an instruction.</p> |
| <p>An item is associated with a format, which defines the item’s payload.</p> |
| <p>All code metadata items of a format named <em>T</em> are grouped under a custom section |
| named <em>‘metadata.code.T’</em>. |
| The following parametrized grammar rules define the generic structure of a code metadata |
| section of format <em>T</em>.</p> |
| <div class="math notranslate nohighlight"> |
| \[\begin{split}\begin{array}{llcll} |
| \def\mathdef1#1{{}}\mathdef1{code metadata section} & \href{binary.html#binary-codemetadata}{\mathtt{codemetadatasec}}(\mathtt{T}) &::=& |
| \href{../../core/binary/modules.html#binary-section}{\mathtt{section}}_0(\href{binary.html#binary-codemetadata}{\mathtt{codemetadata}}(\mathtt{T})) \\ |
| \def\mathdef1#1{{}}\mathdef1{code metadata} & \href{binary.html#binary-codemetadata}{\mathtt{codemetadata}}(\mathtt{T}) &::=& |
| n{:}\href{../../core/binary/values.html#binary-name}{\mathtt{name}} & (\mathrel{\mbox{if}} n = \def\mathdef32#1{\mbox{‘}\mathtt{#1}\mbox{’}}\mathdef32{metadata.code.T}) \\ &&& |
| \href{../../core/binary/conventions.html#binary-list}{\mathtt{list}}(\href{binary.html#binary-codemetadata}{\mathtt{codemetadatafunc}}(\mathtt{T})) \\ |
| \def\mathdef1#1{{}}\mathdef1{code metadata function} & \href{binary.html#binary-codemetadata}{\mathtt{codemetadatafunc}}(\mathtt{T}) &::=& |
| x{:}\href{../../core/binary/modules.html#binary-funcidx}{\mathtt{funcidx}}~\href{../../core/binary/conventions.html#binary-list}{\mathtt{list}}(\href{binary.html#binary-codemetadata}{\mathtt{codemetadataitem}}(\mathtt{T})) \\ |
| \def\mathdef1#1{{}}\mathdef1{code metadata item} & \href{binary.html#binary-codemetadata}{\mathtt{codemetadataitem}}(\mathtt{T}) &::=& |
| \mathit{off}{:}\href{../../core/binary/values.html#binary-int}{\def\mathdef8#1{{\mathtt{u}#1}}\mathdef8{\mathtt{32}}} ~~ \mathit{size}{:}\href{../../core/binary/values.html#binary-int}{\def\mathdef8#1{{\mathtt{u}#1}}\mathdef8{\mathtt{32}}} & (\mathrel{\mbox{if}} \mathit{size} = ||\mathtt{T}||) \\ &&& |
| \mathit{data}{:}\mathtt{T} \\ |
| \end{array}\end{split}\]</div> |
| <p id="index-0">Where <span class="math notranslate nohighlight">\(\mathit{off}\)</span> is the byte offset of the attached instruction, relative to the beginning of the <span class="math notranslate nohighlight">\(\href{../../core/binary/modules.html#binary-func}{\mathtt{func}}\)</span> declaration, and <span class="math notranslate nohighlight">\(\mathit{data}\)</span> is a further payload, whose content depends on the format <span class="math notranslate nohighlight">\(T\)</span>.</p> |
| <p><span class="math notranslate nohighlight">\(\href{binary.html#binary-codemetadata}{\mathtt{codemetadatafunc}}\)</span> entries must appear in order of increasing <span class="math notranslate nohighlight">\(x\)</span>, and duplicate id values are not allowed. <span class="math notranslate nohighlight">\(\href{binary.html#binary-codemetadata}{\mathtt{codemetadata}}\)</span> entries must appear in order of increasing <span class="math notranslate nohighlight">\(\mathit{off}\)</span>, and duplicate offset values are not allowed.</p> |
| <section id="branch-hints"> |
| <span id="binary-branchhints"></span><h3>Branch Hints<a class="headerlink" href="#branch-hints" title="Link to this heading">¶</a></h3> |
| <p>A Branch Hint is a code metadata item with format <em>branch_hint</em>.</p> |
| <p>It can only be attached to <span class="math notranslate nohighlight">\(\href{../../core/syntax/instructions.html#syntax-instr-control}{\mathsf{br\_if}}\)</span> and <span class="math notranslate nohighlight">\(\href{../../core/syntax/instructions.html#syntax-instr-control}{\mathsf{if}}\)</span> instructions.</p> |
| <p>Its payload indicates whether the branch is likely or unlikely to be taken.</p> |
| <p>All branch hints for a module are contained in a single code metadata section |
| with name <em>‘metadata.code.branch_hint’</em>.</p> |
| <div class="math notranslate nohighlight"> |
| \[\begin{split}\begin{array}{llcll} |
| \def\mathdef1#1{{}}\mathdef1{branch hint section} & \href{binary.html#binary-branchhints}{\mathtt{branchhintsec}} &::=& |
| \href{binary.html#binary-codemetadata}{\mathtt{codemetadatasec}}(\href{binary.html#binary-branchhints}{\mathtt{branchhint}}) \\ |
| \def\mathdef1#1{{}}\mathdef1{branch hint} & \href{binary.html#binary-branchhints}{\mathtt{branchhint}} &::=& |
| \href{binary.html#binary-branchhints}{\mathtt{unlikely}} \\ &&|& |
| \href{binary.html#binary-branchhints}{\mathtt{likely}} \\ |
| \def\mathdef1#1{{}}\mathdef1{unlikely} & \href{binary.html#binary-branchhints}{\mathtt{unlikely}} &::=& |
| \def\mathdef33#1{\mathtt{0x#1}}\mathdef33{00} \\ |
| \def\mathdef1#1{{}}\mathdef1{likely} & \href{binary.html#binary-branchhints}{\mathtt{likely}} &::=& |
| \def\mathdef34#1{\mathtt{0x#1}}\mathdef34{01} \\ |
| \end{array}\end{split}\]</div> |
| <p id="index-1">A value of <span class="math notranslate nohighlight">\(\href{binary.html#binary-branchhints}{\mathtt{likely}}\)</span> means that the branch is likely to be taken, while a |
| value of <span class="math notranslate nohighlight">\(\href{binary.html#binary-branchhints}{\mathtt{unlikely}}\)</span> means the opposite. A branch with no hints is considered |
| equally likely to be taken or not.</p> |
| </section> |
| </section> |
| </section> |
| |
| |
| </div> |
| |
| </div> |
| </div> |
| <div class="clearer"></div> |
| </div> |
| <div class="footer"> |
| ©2024, WebAssembly Community Group. |
| |
| </div> |
| |
| |
| |
| |
| </body> |
| </html> |
