README.html - platform/frameworks/compile/libbcc - Gitiles

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 <body>
 <div class="document" id="libbcc-a-versatile-bitcode-execution-engine-for-mobile-devices">
 <h1 class="title">libbcc: A Versatile Bitcode Execution Engine for Mobile Devices</h1>

 <div class="section" id="introduction">
 <h1>Introduction</h1>
 <p>libbcc is an LLVM bitcode execution engine that compiles the bitcode
 to an in-memory executable. libbcc is versatile because:</p>
 <ul class="simple">
 <li>it implements both AOT (Ahead-of-Time) and JIT (Just-in-Time)
 compilation.</li>
 <li>Android devices demand fast start-up time, small size, and high
 performance <em>at the same time</em>. libbcc attempts to address these
 design constraints.</li>
 <li>it supports on-device linking. Each device vendor can supply his or
 her own runtime bitcode library (lib*.bc) that differentiates his or
 her system. Specialization becomes ecosystem-friendly.</li>
 </ul>
 <p>libbcc provides:</p>
 <ul class="simple">
 <li>a <em>just-in-time bitcode compiler</em>, which translates the LLVM bitcode
 into machine code</li>
 <li>a <em>caching mechanism</em>, which can:<ul>
 <li>after each compilation, serialize the in-memory executable into a
 cache file.  Note that the compilation is triggered by a cache
 miss.</li>
 <li>load from the cache file upon cache-hit.</li>
 </ul>
 </li>
 </ul>
 <p>Highlights of libbcc are:</p>
 <ul>
 <li><p class="first">libbcc supports bitcode from various language frontends, such as
 RenderScript, GLSL (pixelflinger2).</p>
 </li>
 <li><p class="first">libbcc strives to balance between library size, launch time and
 steady-state performance:</p>
 <ul>
 <li><p class="first">The size of libbcc is aggressively reduced for mobile devices. We
 customize and improve upon the default Execution Engine from
 upstream. Otherwise, libbcc's execution engine can easily become
 at least 2 times bigger.</p>
 </li>
 <li><p class="first">To reduce launch time, we support caching of
 binaries. Just-in-Time compilation are oftentimes Just-too-Late,
 if the given apps are performance-sensitive. Thus, we implemented
 AOT to get the best of both worlds: Fast launch time and high
 steady-state performance.</p>
 <p>AOT is also important for projects such as NDK on LLVM with
 portability enhancement. Launch time reduction after we
 implemented AOT is signficant:</p>
 <pre class="literal-block">
 Apps          libbcc without AOT       libbcc with AOT
               launch time in libbcc    launch time in libbcc
 App_1            1218ms                   9ms
 App_2            842ms                    4ms
 Wallpaper:
   MagicSmoke     182ms                    3ms
   Halo           127ms                    3ms
 Balls            149ms                    3ms
 SceneGraph       146ms                    90ms
 Model            104ms                    4ms
 Fountain         57ms                     3ms
 </pre>
 <p>AOT also masks the launching time overhead of on-device linking
 and helps it become reality.</p>
 </li>
 <li><p class="first">For steady-state performance, we enable VFP3 and aggressive
 optimizations.</p>
 </li>
 </ul>
 </li>
 <li><p class="first">Currently we disable Lazy JITting.</p>
 </li>
 </ul>
 </div>
 <div class="section" id="api">
 <h1>API</h1>
 <p><strong>Basic:</strong></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> - <em>deprecated</em> - Use bccPrepareExecutableEx instead</li>
 <li><strong>bccPrepareExecutableEx</strong> - Create the in-memory executable by either
 just-in-time compilation or cache loading</li>
 <li><strong>bccGetFuncAddr</strong> - Get the entry address of the function</li>
 <li><strong>bccDisposeScript</strong> - Destroy bcc script and release the resources</li>
 <li><strong>bccGetError</strong> - <em>deprecated</em> - Don't use this</li>
 </ul>
 <p><strong>Reflection:</strong></p>
 <ul class="simple">
 <li><strong>bccGetExportVarCount</strong> - Get the count of exported variables</li>
 <li><strong>bccGetExportVarList</strong> - Get the addresses of exported variables</li>
 <li><strong>bccGetExportFuncCount</strong> - Get the count of exported functions</li>
 <li><strong>bccGetExportFuncList</strong> - Get the addresses of exported functions</li>
 <li><strong>bccGetPragmaCount</strong> - Get the count of pragmas</li>
 <li><strong>bccGetPragmaList</strong> - Get the pragmas</li>
 </ul>
 <p><strong>Debug:</strong></p>
 <ul class="simple">
 <li><strong>bccGetFuncCount</strong> - Get the count of functions (including non-exported)</li>
 <li><strong>bccGetFuncInfoList</strong> - Get the function information (name, base, size)</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 (the endianness,
 the size of off_t, size_t, and ptr_t), and the size
 and 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 resource
 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) -
 The list of the addresses of exported variables.</li>
 <li><strong>Exported Function List</strong> (OBCC_ExportFuncList) -
 The list of the addresses of 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 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>
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	<div class="document" id="libbcc-a-versatile-bitcode-execution-engine-for-mobile-devices">
	<h1 class="title">libbcc: A Versatile Bitcode Execution Engine for Mobile Devices</h1>

	<div class="section" id="introduction">
	<h1>Introduction</h1>
	<p>libbcc is an LLVM bitcode execution engine that compiles the bitcode
	to an in-memory executable. libbcc is versatile because:</p>
	<ul class="simple">
	<li>it implements both AOT (Ahead-of-Time) and JIT (Just-in-Time)
	compilation.</li>
	<li>Android devices demand fast start-up time, small size, and high
	performance <em>at the same time</em>. libbcc attempts to address these
	design constraints.</li>
	<li>it supports on-device linking. Each device vendor can supply his or
	her own runtime bitcode library (lib*.bc) that differentiates his or
	her system. Specialization becomes ecosystem-friendly.</li>
	</ul>
	<p>libbcc provides:</p>
	<ul class="simple">
	<li>a <em>just-in-time bitcode compiler</em>, which translates the LLVM bitcode
	into machine code</li>
	<li>a <em>caching mechanism</em>, which can:<ul>
	<li>after each compilation, serialize the in-memory executable into a
	cache file. Note that the compilation is triggered by a cache
	miss.</li>
	<li>load from the cache file upon cache-hit.</li>
	</ul>
	</li>
	</ul>
	<p>Highlights of libbcc are:</p>
	<ul>
	<li><p class="first">libbcc supports bitcode from various language frontends, such as
	RenderScript, GLSL (pixelflinger2).</p>
	</li>
	<li><p class="first">libbcc strives to balance between library size, launch time and
	steady-state performance:</p>
	<ul>
	<li><p class="first">The size of libbcc is aggressively reduced for mobile devices. We
	customize and improve upon the default Execution Engine from
	upstream. Otherwise, libbcc's execution engine can easily become
	at least 2 times bigger.</p>
	</li>
	<li><p class="first">To reduce launch time, we support caching of
	binaries. Just-in-Time compilation are oftentimes Just-too-Late,
	if the given apps are performance-sensitive. Thus, we implemented
	AOT to get the best of both worlds: Fast launch time and high
	steady-state performance.</p>
	<p>AOT is also important for projects such as NDK on LLVM with
	portability enhancement. Launch time reduction after we
	implemented AOT is signficant:</p>
	<pre class="literal-block">
	Apps libbcc without AOT libbcc with AOT
	launch time in libbcc launch time in libbcc
	App_1 1218ms 9ms
	App_2 842ms 4ms
	Wallpaper:
	MagicSmoke 182ms 3ms
	Halo 127ms 3ms
	Balls 149ms 3ms
	SceneGraph 146ms 90ms
	Model 104ms 4ms
	Fountain 57ms 3ms
	</pre>
	<p>AOT also masks the launching time overhead of on-device linking
	and helps it become reality.</p>
	</li>
	<li><p class="first">For steady-state performance, we enable VFP3 and aggressive
	optimizations.</p>
	</li>
	</ul>
	</li>
	<li><p class="first">Currently we disable Lazy JITting.</p>
	</li>
	</ul>
	</div>
	<div class="section" id="api">
	<h1>API</h1>
	<p><strong>Basic:</strong></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> - <em>deprecated</em> - Use bccPrepareExecutableEx instead</li>
	<li><strong>bccPrepareExecutableEx</strong> - Create the in-memory executable by either
	just-in-time compilation or cache loading</li>
	<li><strong>bccGetFuncAddr</strong> - Get the entry address of the function</li>
	<li><strong>bccDisposeScript</strong> - Destroy bcc script and release the resources</li>
	<li><strong>bccGetError</strong> - <em>deprecated</em> - Don't use this</li>
	</ul>
	<p><strong>Reflection:</strong></p>
	<ul class="simple">
	<li><strong>bccGetExportVarCount</strong> - Get the count of exported variables</li>
	<li><strong>bccGetExportVarList</strong> - Get the addresses of exported variables</li>
	<li><strong>bccGetExportFuncCount</strong> - Get the count of exported functions</li>
	<li><strong>bccGetExportFuncList</strong> - Get the addresses of exported functions</li>
	<li><strong>bccGetPragmaCount</strong> - Get the count of pragmas</li>
	<li><strong>bccGetPragmaList</strong> - Get the pragmas</li>
	</ul>
	<p><strong>Debug:</strong></p>
	<ul class="simple">
	<li><strong>bccGetFuncCount</strong> - Get the count of functions (including non-exported)</li>
	<li><strong>bccGetFuncInfoList</strong> - Get the function information (name, base, size)</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 (the endianness,
	the size of off_t, size_t, and ptr_t), and the size
	and 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 resource
	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) -
	The list of the addresses of exported variables.</li>
	<li><strong>Exported Function List</strong> (OBCC_ExportFuncList) -
	The list of the addresses of 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 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>
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