</li>
</ul>
-</div><section id="introduction">
-<h2 id="introduction">Introduction</h2>
+</div><h2 id="introduction">Introduction</h2>
<p>This document is a reference manual for the PNaCl bitcode format. It describes
the bitcode on a <em>semantic</em> level; the physical encoding level will be described
elsewhere. For the purpose of this document, the textual form of LLVM IR is
of the LLVM language reference manual. Only the changes, restrictions
and variations specific to PNaCl are described—full semantic
descriptions are not duplicated from the LLVM reference manual.</p>
-</section><section id="high-level-structure">
<h2 id="high-level-structure">High Level Structure</h2>
<p>A PNaCl portable executable (<strong>pexe</strong> in short) is a single LLVM IR module.</p>
-<section id="data-model">
<h3 id="data-model">Data Model</h3>
<p>The data model for PNaCl bitcode is fixed at little-endian ILP32: pointers are
32 bits in size. 64-bit integer types are also supported natively via the i64
<code>long long</code>).</p>
<p>Floating point support is fixed at IEEE 754 32-bit and 64-bit values (f32 and
f64, respectively).</p>
-</section><section id="linkage-types">
-<span id="bitcode-linkagetypes"></span><h3 id="linkage-types"><span id="bitcode-linkagetypes"></span>Linkage Types</h3>
+<h3 id="linkage-types"><span id="bitcode-linkagetypes"></span>Linkage Types</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#linkage">LLVM LangRef: Linkage Types</a></p>
<p>The linkage types supported by PNaCl bitcode are <code>internal</code> and <code>external</code>.
A single function in the pexe, named <code>_start</code>, has the linkage type
<code>external</code>. All the other functions and globals have the linkage type
<code>internal</code>.</p>
-</section><section id="calling-conventions">
<h3 id="calling-conventions">Calling Conventions</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#callingconv">LLVM LangRef: Calling Conventions</a></p>
<p>The only calling convention supported by PNaCl bitcode is <code>ccc</code> - the C
calling convention.</p>
-</section><section id="visibility-styles">
<h3 id="visibility-styles">Visibility Styles</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#visibility-styles">LLVM LangRef: Visibility Styles</a></p>
<p>PNaCl bitcode does not support visibility styles.</p>
-</section><section id="global-variables">
-<span id="bitcode-globalvariables"></span><h3 id="global-variables"><span id="bitcode-globalvariables"></span>Global Variables</h3>
+<h3 id="global-variables"><span id="bitcode-globalvariables"></span>Global Variables</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#globalvars">LLVM LangRef: Global Variables</a></p>
<p>Restrictions on global variables:</p>
<ul class="small-gap">
</pre>
<p>A <em>CompoundElement</em> is a unnamed, packed struct containing more than one
<em>SimpleElement</em>.</p>
-</section><section id="functions">
<h3 id="functions">Functions</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#functionstructure">LLVM LangRef: Functions</a></p>
<p>The restrictions on <a class="reference internal" href="#bitcode-linkagetypes"><em>linkage types</em></a>, calling
<li>Functions with a variable number of arguments (<em>vararg</em>).</li>
<li>Alignment (<code>align</code>).</li>
</ul>
-</section><section id="aliases">
<h3 id="aliases">Aliases</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#aliases">LLVM LangRef: Aliases</a></p>
<p>PNaCl bitcode does not support aliases.</p>
-</section><section id="named-metadata">
<h3 id="named-metadata">Named Metadata</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#namedmetadatastructure">LLVM LangRef: Named Metadata</a></p>
<p>While PNaCl bitcode has provisions for debugging metadata, it is not considered
part of the stable ABI. It exists for tool support and should not appear in
distributed pexes.</p>
<p>Other kinds of LLVM metadata are not supported.</p>
-</section><section id="module-level-inline-assembly">
<h3 id="module-level-inline-assembly">Module-Level Inline Assembly</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#moduleasm">LLVM LangRef: Module-Level Inline Assembly</a></p>
<p>PNaCl bitcode does not support inline assembly.</p>
-</section><section id="volatile-memory-accesses">
<h3 id="volatile-memory-accesses">Volatile Memory Accesses</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#volatile">LLVM LangRef: Volatile Memory Accesses</a></p>
<p>PNaCl bitcode does not support volatile memory accesses. The
<code>volatile</code> attribute on loads and stores is not supported. See the
<a class="reference internal" href="/native-client/reference/pnacl-c-cpp-language-support.html"><em>PNaCl C/C++ Language Support</em></a> for more details.</p>
-</section><section id="memory-model-for-concurrent-operations">
<h3 id="memory-model-for-concurrent-operations">Memory Model for Concurrent Operations</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#memmodel">LLVM LangRef: Memory Model for Concurrent Operations</a></p>
<p>See the <a class="reference external" href="PNaClDeveloperGuide.html">PNaCl Developer’s Guide</a> for more
details.</p>
-</section><section id="fast-math-flags">
<h3 id="fast-math-flags">Fast-Math Flags</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#fastmath">LLVM LangRef: Fast-Math Flags</a></p>
<p>Fast-math mode is not currently supported by the PNaCl bitcode.</p>
-</section></section><section id="type-system">
<h2 id="type-system">Type System</h2>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#typesystem">LLVM LangRef: Type System</a></p>
<p>The LLVM types allowed in PNaCl bitcode are restricted, as follows:</p>
-<section id="scalar-types">
<h3 id="scalar-types">Scalar types</h3>
<ul class="small-gap">
<li><p class="first">The only scalar types allowed are integer, float (32-bit floating point),
</ul>
</li>
</ul>
-</section><section id="vector-types">
<h3 id="vector-types">Vector types</h3>
<p>The only vector types allowed are:</p>
<ul class="small-gap">
element counts listed previously (their width is therefore not
128-bits).</li>
</ul>
-</section><section id="array-and-struct-types">
<h3 id="array-and-struct-types">Array and struct types</h3>
<p>Array and struct types are only allowed in
<a class="reference internal" href="#bitcode-globalvariables"><em>global variable initializers</em></a>.</p>
-</section><section id="pointer-types">
-<span id="bitcode-pointertypes"></span><h3 id="pointer-types"><span id="bitcode-pointertypes"></span>Pointer types</h3>
+<h3 id="pointer-types"><span id="bitcode-pointertypes"></span>Pointer types</h3>
<p>Only the following pointer types are allowed:</p>
<ul class="small-gap">
-<li>Pointers to valid PNaCl bitcode scalar types, as specified above.</li>
+<li>Pointers to valid PNaCl bitcode scalar types, as specified above, except for
+<code>i1</code>.</li>
+<li>Pointers to valid PNaCl bitcode vector types, as specified above, except for
+<code><? x i1></code>.</li>
<li>Pointers to functions.</li>
</ul>
<p>In addition, the address space for all pointers must be 0.</p>
<li>Is the return value of a <code>bitcast</code> instruction.</li>
<li>Is the return value of a <code>inttoptr</code> instruction.</li>
</ul>
-</section><section id="undefined-values">
<h3 id="undefined-values">Undefined Values</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#undefvalues">LLVM LangRef: Undefined Values</a></p>
<p><code>undef</code> is only allowed within functions, not in global variable initializers.</p>
-</section><section id="constant-expressions">
<h3 id="constant-expressions">Constant Expressions</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#constant-expressions">LLVM LangRef: Constant Expressions</a></p>
<p>Constant expressions are only allowed in
<a class="reference internal" href="#bitcode-globalvariables"><em>global variable initializers</em></a>.</p>
-</section></section><section id="other-values">
<h2 id="other-values">Other Values</h2>
-<section id="metadata-nodes-and-metadata-strings">
<h3 id="metadata-nodes-and-metadata-strings">Metadata Nodes and Metadata Strings</h3>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#metadata">LLVM LangRef: Metadata Nodes and Metadata Strings</a></p>
<p>While PNaCl bitcode has provisions for debugging metadata, it is not considered
part of the stable ABI. It exists for tool support and should not appear in
distributed pexes.</p>
<p>Other kinds of LLVM metadata are not supported.</p>
-</section></section><section id="intrinsic-global-variables">
<h2 id="intrinsic-global-variables">Intrinsic Global Variables</h2>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#intrinsic-global-variables">LLVM LangRef: Intrinsic Global Variables</a></p>
<p>PNaCl bitcode does not support intrinsic global variables.</p>
-</section><section id="errno-and-errors-in-arithmetic-instructions">
-<span id="ir-and-errno"></span><h2 id="errno-and-errors-in-arithmetic-instructions"><span id="ir-and-errno"></span>Errno and errors in arithmetic instructions</h2>
+<h2 id="errno-and-errors-in-arithmetic-instructions"><span id="ir-and-errno"></span>Errno and errors in arithmetic instructions</h2>
<p>Some arithmetic instructions and intrinsics have the similar semantics to
libc math functions, but differ in the treatment of <code>errno</code>. While the
libc functions may set <code>errno</code> for domain errors, the instructions and
intrinsics do not. This is because the variable <code>errno</code> is not special
and is not required to be part of the program.</p>
-</section><section id="instruction-reference">
<h2 id="instruction-reference">Instruction Reference</h2>
-<section id="list-of-allowed-instructions">
<h3 id="list-of-allowed-instructions">List of allowed instructions</h3>
<p>This is a list of LLVM instructions supported by PNaCl bitcode. Where
applicable, PNaCl-specific restrictions are provided.</p>
<li><p class="first"><code>load</code>, <code>store</code></p>
<p>The pointer argument of these instructions must be a <em>normalized</em> pointer (see
<a class="reference internal" href="#bitcode-pointertypes"><em>pointer types</em></a>). The <code>volatile</code> and <code>atomic</code>
-attributes are not supported. Loads and stores of the type <code>i1</code> are not
-supported.</p>
-<p>These instructions must use <code>align 1</code> on integer memory accesses, <code>align 4</code>
-for <code>float</code> accesses and <code>align 8</code> for <code>double</code> accesses.</p>
+attributes are not supported. Loads and stores of the type <code>i1</code> and <code><? x
+i1></code> are not supported.</p>
+<p>These instructions must follow the following alignment restrictions:</p>
+<ul class="small-gap">
+<li>On integer memory accesses: <code>align 1</code>.</li>
+<li>On <code>float</code> memory accesses: <code>align 1</code> or <code>align 4</code>.</li>
+<li>On <code>double</code> memory accesses: <code>align 1</code> or <code>align 8</code>.</li>
+<li>On vector memory accesses: alignment at the vector’s element width, for
+example <code><4 x i32></code> must be <code>align 4</code>.</li>
+</ul>
</li>
<li><code>trunc</code></li>
<li><code>zext</code></li>
<li><code>insertelement</code></li>
<li><code>extractelement</code></li>
</ul>
-</section><section id="alloca">
-<span id="bitcode-allocainst"></span><h3 id="alloca"><span id="bitcode-allocainst"></span><code>alloca</code></h3>
+<h3 id="alloca"><span id="bitcode-allocainst"></span><code>alloca</code></h3>
<p>The only allowed type for <code>alloca</code> instructions in PNaCl bitcode is i8. The
size argument must be an i32. For example:</p>
<pre>
%buf = alloca i8, i32 8, align 4
</pre>
-</section></section><section id="intrinsic-functions">
<h2 id="intrinsic-functions">Intrinsic Functions</h2>
<p><a class="reference external" href="http://llvm.org/releases/3.3/docs/LangRef.html#intrinsics">LLVM LangRef: Intrinsic Functions</a></p>
-<section id="list-of-allowed-intrinsics">
<h3 id="list-of-allowed-intrinsics">List of allowed intrinsics</h3>
<p>The only intrinsics supported by PNaCl bitcode are the following.</p>
<ul class="small-gap">
<p>See <a class="reference internal" href="#bitcode-atomicintrinsics"><em>atomic intrinsics</em></a>.</p>
</li>
</ul>
-</section><section id="thread-pointer-related-intrinsics">
-<span id="bitcode-threadpointerintrinsics"></span><h3 id="thread-pointer-related-intrinsics"><span id="bitcode-threadpointerintrinsics"></span>Thread pointer related intrinsics</h3>
+<h3 id="thread-pointer-related-intrinsics"><span id="bitcode-threadpointerintrinsics"></span>Thread pointer related intrinsics</h3>
<pre>
declare i8* @llvm.nacl.read.tp()
</pre>
<p>Returns a read-only thread pointer. The value is controlled by the embedding
sandbox’s runtime.</p>
-</section><section id="setjmp-and-longjmp">
-<span id="bitcode-setjmplongjmp"></span><h3 id="setjmp-and-longjmp"><span id="bitcode-setjmplongjmp"></span>Setjmp and Longjmp</h3>
+<h3 id="setjmp-and-longjmp"><span id="bitcode-setjmplongjmp"></span>Setjmp and Longjmp</h3>
<pre>
declare void @llvm.nacl.longjmp(i8* %jmpbuf, i32)
declare i32 @llvm.nacl.setjmp(i8* %jmpbuf)
<p>These intrinsics implement the semantics of C11 <code>setjmp</code> and <code>longjmp</code>. The
<code>jmpbuf</code> pointer must be 64-bit aligned and point to at least 1024 bytes of
allocated memory.</p>
-</section><section id="atomic-intrinsics">
-<span id="bitcode-atomicintrinsics"></span><h3 id="atomic-intrinsics"><span id="bitcode-atomicintrinsics"></span>Atomic intrinsics</h3>
+<h3 id="atomic-intrinsics"><span id="bitcode-atomicintrinsics"></span>Atomic intrinsics</h3>
<pre>
declare iN @llvm.nacl.atomic.load.<size>(
iN* <source>, i32 <memory_order>)
function from header <code><stdatomic.h></code> and the C++11 <code>is_lock_free</code>
member function in header <code><atomic></code>. It can be used through the
<code>__nacl_atomic_is_lock_free</code> builtin.</p>
-</section></section></section>
+</section>
{{/partials.standard_nacl_article}}
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