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+<body>
+<div class="document" id="libbcc-a-versatile-bitcode-execution-engine">
+<h1 class="title">libbcc: A Versatile Bitcode Execution Engine</h1>
+
+<div class="section" id="introduction">
+<h1>Introduction</h1>
+<p>libbcc is an LLVM bitcode execution engine which compiles the bitcode
+to an in-memory executable. libbcc provides a <em>just-in-time bitcode
+compiler</em>, which translates the bitcode into machine code, and a <em>caching
+mechanism</em>, which saves the in-memory executable after the compilation.
+Here are some highlights of libbcc:</p>
+<ul class="simple">
+<li>libbcc supports bit code from various language frontends, such as
+RenderScript, GLSL.</li>
+<li>libbcc strives to balance between library size, launch time and
+steady-state performance:<ul>
+<li>The size of libbcc is aggressively reduced for a mobile device.
+We customize and we don't use Execution Engine.</li>
+<li>To reduce launch time, we support caching of binaries.</li>
+<li>For steady-state performance, we enable VFP3 and aggressive
+optimizations.</li>
+</ul>
+</li>
+<li>Currently we disable Lazy JITting.</li>
+</ul>
+</div>
+<div class="section" id="api">
+<h1>API</h1>
+<p>Basic:</p>
+<ul class="simple">
+<li><strong>bccCreateScript</strong> - Create new bcc script</li>
+<li><strong>bccRegisterSymbolCallback</strong> - Register the callback function for external
+symbol lookup</li>
+<li><strong>bccReadBC</strong> - Set the source bitcode for compilation</li>
+<li><strong>bccReadModule</strong> - Set the llvm::Module for compilation</li>
+<li><strong>bccLinkBC</strong> - Set the library bitcode for linking</li>
+<li><strong>bccPrepareExecutable</strong> Create the in-memory executable by either
+just-in-time compilation or cache loading</li>
+<li><strong>bccDeleteScript</strong> - Destroy bcc script and release the resources</li>
+<li><strong>bccGetError</strong> - Get the error code</li>
+<li><strong>bccGetScriptInfoLog</strong> <em>deprecated</em> - Don't use this</li>
+</ul>
+<p>Reflection:</p>
+<ul class="simple">
+<li><strong>bccGetExportVars</strong> - Get the addresses of exported variables</li>
+<li><strong>bccGetExportFuncs</strong> - Get the addresses of exported functions</li>
+<li><strong>bccGetPragmas</strong> - Get the pragmas</li>
+</ul>
+<p>Debug:</p>
+<ul class="simple">
+<li><strong>bccGetFunctions</strong> - Get the function name list</li>
+<li><strong>bccGetFunctionBinary</strong> - Get the address and the size of function binary</li>
+</ul>
+</div>
+<div class="section" id="cache-file-format">
+<h1>Cache File Format</h1>
+<p>A cache file (denoted as *.oBCC) for libbcc consists of several sections:
+header, string pool, dependencies table, relocation table, exported
+variable list, exported function list, pragma list, function information
+table, and bcc context. Every section should be aligned to a word size.
+Here is the brief description of each sections:</p>
+<ul class="simple">
+<li><strong>Header</strong> (OBCC_Header) - The header of a cache file. It contains the
+magic word, version, machine integer type information, and the size
+and the offset of other sections. The header section is guaranteed
+to be at the beginning of the cache file.</li>
+<li><strong>String Pool</strong> (OBCC_StringPool) - A collection of serialized variable
+length strings. The strp_index in the other part of the cache file
+represents the index of such string in this string pool.</li>
+<li><strong>Dependencies Table</strong> (OBCC_DependencyTable) - The dependencies table.
+This table stores the resource name (or file path), the resouece
+type (rather in APK or on the file system), and the SHA1 checksum.</li>
+<li><strong>Relocation Table</strong> (OBCC_RelocationTable) - <em>not enabled</em></li>
+<li><strong>Exported Variable List</strong> (OBCC_ExportVarList),
+<strong>Exported Function List</strong> (OBCC_ExportFuncList) -
+The list of the addresses of exported variables and exported functions.</li>
+<li><strong>Pragma List</strong> (OBCC_PragmaList) - The list of pragma key-value pair.</li>
+<li><strong>Function Information Table</strong> (OBCC_FuncTable) - This is a table of
+function information, such as function name, function entry address,
+and function binary size. Besides, the table should be ordered by
+function name.</li>
+<li><strong>Context</strong> - The context of the in-memory executable, including
+the code and the data. The offset of context should aligned to
+a page size, so that we can mmap the context directly into the memory.</li>
+</ul>
+<p>For furthur information, you may read <a class="reference external" href="include/bcc/bcc_cache.h">bcc_cache.h</a>,
+<a class="reference external" href="lib/bcc/CacheReader.cpp">CacheReader.cpp</a>, and
+<a class="reference external" href="lib/bcc/CacheWriter.cpp">CacheWriter.cpp</a> for details.</p>
+</div>
+<div class="section" id="jit-ed-code-calling-conventions">
+<h1>JIT'ed Code Calling Conventions</h1>
+<ol class="arabic">
+<li><p class="first">Calls from Execution Environment or from/to within script:</p>
+<p>On ARM, the first 4 arguments will go into r0, r1, r2, and r3, in that order.
+The remaining (if any) will go through stack.</p>
+<p>For ext_vec_types such as float2, a set of registers will be used. In the case
+of float2, a register pair will be used. Specifically, if float2 is the first
+argument in the function prototype, float2.x will go into r0, and float2.y,
+r1.</p>
+<p>Note: stack will be aligned to the coarsest-grained argument. In the case of
+float2 above as an argument, parameter stack will be aligned to an 8-byte
+boundary (if the sizes of other arguments are no greater than 8.)</p>
+</li>
+<li><p class="first">Calls from/to a separate compilation unit: (E.g., calls to Execution
+Environment if those runtime library callees are not compiled using LLVM.)</p>
+<p>On ARM, we use hardfp. Note that double will be placed in a register pair.</p>
+</li>
+</ol>
+</div>
+</div>
+</body>
+</html>