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gerrit-public.fairphone.software / platform / frameworks / compile / libbcc / cecdab21b205a7cd8910e25c540d57bf4c709aa4 / . / README.html
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Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]7<title>libbcc: A Versatile Bitcode Execution Engine for Mobile Devices</title>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]8<style type="text/css">
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Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]307<div class="document" id="libbcc-a-versatile-bitcode-execution-engine-for-mobile-devices">
308<h1 class="title">libbcc: A Versatile Bitcode Execution Engine for Mobile Devices</h1>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]309
310<div class="section" id="introduction">
311<h1>Introduction</h1>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]312<p>libbcc is an LLVM bitcode execution engine that compiles the bitcode
Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]313to an in-memory executable. libbcc is versatile because:</p>
314<ul class="simple">
315<li>it implements both AOT (Ahead-of-Time) and JIT (Just-in-Time) compilation.</li>
316<li>Android devices demand fast start-up time, small size and high performance.</li>
317</ul>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]318<p>libbcc provides:</p>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]319<ul class="simple">
Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]320<li>a <em>just-in-time bitcode compiler</em>, which translates the bitcode into
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]321machine code</li>
322<li>a <em>caching mechanism</em>, which can:<ul>
Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]323<li>after each compilation, serialize the in-memory executable into a cache file.
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]324Note that the compilation is triggered by a cache miss.</li>
325<li>load from the cache file upon cache-hit.</li>
326</ul>
327</li>
328</ul>
329<p>Here are some highlights of libbcc:</p>
330<ul class="simple">
331<li>libbcc supports bitcode from various language frontends, such as
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]332RenderScript, GLSL.</li>
333<li>libbcc strives to balance between library size, launch time and
334steady-state performance:<ul>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]335<li>The size of libbcc is aggressively reduced for mobile devices.
Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]336We customize and we don't use the default Execution Engine from upstream.</li>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]337<li>To reduce launch time, we support caching of binaries.</li>
338<li>For steady-state performance, we enable VFP3 and aggressive
339optimizations.</li>
340</ul>
341</li>
342<li>Currently we disable Lazy JITting.</li>
343</ul>
344</div>
345<div class="section" id="api">
346<h1>API</h1>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]347<p><strong>Basic:</strong></p>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]348<ul class="simple">
349<li><strong>bccCreateScript</strong> - Create new bcc script</li>
350<li><strong>bccRegisterSymbolCallback</strong> - Register the callback function for external
351symbol lookup</li>
352<li><strong>bccReadBC</strong> - Set the source bitcode for compilation</li>
353<li><strong>bccReadModule</strong> - Set the llvm::Module for compilation</li>
354<li><strong>bccLinkBC</strong> - Set the library bitcode for linking</li>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]355<li><strong>bccPrepareExecutable</strong> - Create the in-memory executable by either
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]356just-in-time compilation or cache loading</li>
357<li><strong>bccDeleteScript</strong> - Destroy bcc script and release the resources</li>
358<li><strong>bccGetError</strong> - Get the error code</li>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]359<li><strong>bccGetScriptInfoLog</strong> - <em>deprecated</em> - Don't use this</li>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]360</ul>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]361<p><strong>Reflection:</strong></p>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]362<ul class="simple">
363<li><strong>bccGetExportVars</strong> - Get the addresses of exported variables</li>
364<li><strong>bccGetExportFuncs</strong> - Get the addresses of exported functions</li>
365<li><strong>bccGetPragmas</strong> - Get the pragmas</li>
366</ul>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]367<p><strong>Debug:</strong></p>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]368<ul class="simple">
369<li><strong>bccGetFunctions</strong> - Get the function name list</li>
Shih-wei Liao7fff2282011-01-09 13:57:01 -0800[diff] [blame]370<li><strong>bccGetFunctionBinary</strong> - Get the address and the size of a function binary</li>
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]371</ul>
372</div>
373<div class="section" id="cache-file-format">
374<h1>Cache File Format</h1>
375<p>A cache file (denoted as *.oBCC) for libbcc consists of several sections:
376header, string pool, dependencies table, relocation table, exported
377variable list, exported function list, pragma list, function information
378table, and bcc context. Every section should be aligned to a word size.
379Here is the brief description of each sections:</p>
380<ul class="simple">
381<li><strong>Header</strong> (OBCC_Header) - The header of a cache file. It contains the
Shih-wei Liaocecdab22011-01-10 02:10:29 -0800[diff] [blame^]382magic word, version, machine integer type information (the endianness,
383the size of off_t, size_t, and ptr_t), and the size
384and offset of other sections. The header section is guaranteed
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]385to be at the beginning of the cache file.</li>
386<li><strong>String Pool</strong> (OBCC_StringPool) - A collection of serialized variable
387length strings. The strp_index in the other part of the cache file
388represents the index of such string in this string pool.</li>
389<li><strong>Dependencies Table</strong> (OBCC_DependencyTable) - The dependencies table.
Shih-wei Liao8538dfa2011-01-09 15:42:28 -0800[diff] [blame]390This table stores the resource name (or file path), the resource
Shih-wei Liaoe961c662011-01-09 04:42:39 -0800[diff] [blame]391type (rather in APK or on the file system), and the SHA1 checksum.</li>
392<li><strong>Relocation Table</strong> (OBCC_RelocationTable) - <em>not enabled</em></li>
393<li><strong>Exported Variable List</strong> (OBCC_ExportVarList),
394<strong>Exported Function List</strong> (OBCC_ExportFuncList) -
395The list of the addresses of exported variables and exported functions.</li>
396<li><strong>Pragma List</strong> (OBCC_PragmaList) - The list of pragma key-value pair.</li>
397<li><strong>Function Information Table</strong> (OBCC_FuncTable) - This is a table of
398function information, such as function name, function entry address,
399and function binary size. Besides, the table should be ordered by
400function name.</li>
401<li><strong>Context</strong> - The context of the in-memory executable, including
402the code and the data. The offset of context should aligned to
403a page size, so that we can mmap the context directly into the memory.</li>
404</ul>
405<p>For furthur information, you may read <a class="reference external" href="include/bcc/bcc_cache.h">bcc_cache.h</a>,
406<a class="reference external" href="lib/bcc/CacheReader.cpp">CacheReader.cpp</a>, and
407<a class="reference external" href="lib/bcc/CacheWriter.cpp">CacheWriter.cpp</a> for details.</p>
408</div>
409<div class="section" id="jit-ed-code-calling-conventions">
410<h1>JIT'ed Code Calling Conventions</h1>
411<ol class="arabic">
412<li><p class="first">Calls from Execution Environment or from/to within script:</p>
413<p>On ARM, the first 4 arguments will go into r0, r1, r2, and r3, in that order.
414The remaining (if any) will go through stack.</p>
415<p>For ext_vec_types such as float2, a set of registers will be used. In the case
416of float2, a register pair will be used. Specifically, if float2 is the first
417argument in the function prototype, float2.x will go into r0, and float2.y,
418r1.</p>
419<p>Note: stack will be aligned to the coarsest-grained argument. In the case of
420float2 above as an argument, parameter stack will be aligned to an 8-byte
421boundary (if the sizes of other arguments are no greater than 8.)</p>
422</li>
423<li><p class="first">Calls from/to a separate compilation unit: (E.g., calls to Execution
424Environment if those runtime library callees are not compiled using LLVM.)</p>
425<p>On ARM, we use hardfp. Note that double will be placed in a register pair.</p>
426</li>
427</ol>
428</div>
429</div>
430</body>
431</html>