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| 306 | <body> |
| 307 | <div class="document" id="libbcc-a-versatile-bitcode-execution-engine"> |
| 308 | <h1 class="title">libbcc: A Versatile Bitcode Execution Engine</h1> |
| 309 | |
| 310 | <div class="section" id="introduction"> |
| 311 | <h1>Introduction</h1> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 312 | <p>libbcc is an LLVM bitcode execution engine that compiles the bitcode |
| 313 | to an in-memory executable.</p> |
| 314 | <p>libbcc provides:</p> |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 315 | <ul class="simple"> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 316 | <li>a <em>just-in-time (JIT) bitcode compiler</em>, which translates the bitcode into |
| 317 | machine code</li> |
| 318 | <li>a <em>caching mechanism</em>, which can:<ul> |
| 319 | <li>after the compilation, serialize the in-memory executable into a cache file. |
| 320 | Note that the compilation is triggered by a cache miss.</li> |
| 321 | <li>load from the cache file upon cache-hit.</li> |
| 322 | </ul> |
| 323 | </li> |
| 324 | </ul> |
| 325 | <p>Here are some highlights of libbcc:</p> |
| 326 | <ul class="simple"> |
| 327 | <li>libbcc supports bitcode from various language frontends, such as |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 328 | RenderScript, GLSL.</li> |
| 329 | <li>libbcc strives to balance between library size, launch time and |
| 330 | steady-state performance:<ul> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 331 | <li>The size of libbcc is aggressively reduced for mobile devices. |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 332 | We customize and we don't use Execution Engine.</li> |
| 333 | <li>To reduce launch time, we support caching of binaries.</li> |
| 334 | <li>For steady-state performance, we enable VFP3 and aggressive |
| 335 | optimizations.</li> |
| 336 | </ul> |
| 337 | </li> |
| 338 | <li>Currently we disable Lazy JITting.</li> |
| 339 | </ul> |
| 340 | </div> |
| 341 | <div class="section" id="api"> |
| 342 | <h1>API</h1> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 343 | <p><strong>Basic:</strong></p> |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 344 | <ul class="simple"> |
| 345 | <li><strong>bccCreateScript</strong> - Create new bcc script</li> |
| 346 | <li><strong>bccRegisterSymbolCallback</strong> - Register the callback function for external |
| 347 | symbol lookup</li> |
| 348 | <li><strong>bccReadBC</strong> - Set the source bitcode for compilation</li> |
| 349 | <li><strong>bccReadModule</strong> - Set the llvm::Module for compilation</li> |
| 350 | <li><strong>bccLinkBC</strong> - Set the library bitcode for linking</li> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 351 | <li><strong>bccPrepareExecutable</strong> - Create the in-memory executable by either |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 352 | just-in-time compilation or cache loading</li> |
| 353 | <li><strong>bccDeleteScript</strong> - Destroy bcc script and release the resources</li> |
| 354 | <li><strong>bccGetError</strong> - Get the error code</li> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 355 | <li><strong>bccGetScriptInfoLog</strong> - <em>deprecated</em> - Don't use this</li> |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 356 | </ul> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 357 | <p><strong>Reflection:</strong></p> |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 358 | <ul class="simple"> |
| 359 | <li><strong>bccGetExportVars</strong> - Get the addresses of exported variables</li> |
| 360 | <li><strong>bccGetExportFuncs</strong> - Get the addresses of exported functions</li> |
| 361 | <li><strong>bccGetPragmas</strong> - Get the pragmas</li> |
| 362 | </ul> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 363 | <p><strong>Debug:</strong></p> |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 364 | <ul class="simple"> |
| 365 | <li><strong>bccGetFunctions</strong> - Get the function name list</li> |
Shih-wei Liao | 7fff228 | 2011-01-09 13:57:01 -0800 | [diff] [blame] | 366 | <li><strong>bccGetFunctionBinary</strong> - Get the address and the size of a function binary</li> |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 367 | </ul> |
| 368 | </div> |
| 369 | <div class="section" id="cache-file-format"> |
| 370 | <h1>Cache File Format</h1> |
| 371 | <p>A cache file (denoted as *.oBCC) for libbcc consists of several sections: |
| 372 | header, string pool, dependencies table, relocation table, exported |
| 373 | variable list, exported function list, pragma list, function information |
| 374 | table, and bcc context. Every section should be aligned to a word size. |
| 375 | Here is the brief description of each sections:</p> |
| 376 | <ul class="simple"> |
| 377 | <li><strong>Header</strong> (OBCC_Header) - The header of a cache file. It contains the |
| 378 | magic word, version, machine integer type information, and the size |
| 379 | and the offset of other sections. The header section is guaranteed |
| 380 | to be at the beginning of the cache file.</li> |
| 381 | <li><strong>String Pool</strong> (OBCC_StringPool) - A collection of serialized variable |
| 382 | length strings. The strp_index in the other part of the cache file |
| 383 | represents the index of such string in this string pool.</li> |
| 384 | <li><strong>Dependencies Table</strong> (OBCC_DependencyTable) - The dependencies table. |
Shih-wei Liao | 8538dfa | 2011-01-09 15:42:28 -0800 | [diff] [blame^] | 385 | This table stores the resource name (or file path), the resource |
Shih-wei Liao | e961c66 | 2011-01-09 04:42:39 -0800 | [diff] [blame] | 386 | type (rather in APK or on the file system), and the SHA1 checksum.</li> |
| 387 | <li><strong>Relocation Table</strong> (OBCC_RelocationTable) - <em>not enabled</em></li> |
| 388 | <li><strong>Exported Variable List</strong> (OBCC_ExportVarList), |
| 389 | <strong>Exported Function List</strong> (OBCC_ExportFuncList) - |
| 390 | The list of the addresses of exported variables and exported functions.</li> |
| 391 | <li><strong>Pragma List</strong> (OBCC_PragmaList) - The list of pragma key-value pair.</li> |
| 392 | <li><strong>Function Information Table</strong> (OBCC_FuncTable) - This is a table of |
| 393 | function information, such as function name, function entry address, |
| 394 | and function binary size. Besides, the table should be ordered by |
| 395 | function name.</li> |
| 396 | <li><strong>Context</strong> - The context of the in-memory executable, including |
| 397 | the code and the data. The offset of context should aligned to |
| 398 | a page size, so that we can mmap the context directly into the memory.</li> |
| 399 | </ul> |
| 400 | <p>For furthur information, you may read <a class="reference external" href="include/bcc/bcc_cache.h">bcc_cache.h</a>, |
| 401 | <a class="reference external" href="lib/bcc/CacheReader.cpp">CacheReader.cpp</a>, and |
| 402 | <a class="reference external" href="lib/bcc/CacheWriter.cpp">CacheWriter.cpp</a> for details.</p> |
| 403 | </div> |
| 404 | <div class="section" id="jit-ed-code-calling-conventions"> |
| 405 | <h1>JIT'ed Code Calling Conventions</h1> |
| 406 | <ol class="arabic"> |
| 407 | <li><p class="first">Calls from Execution Environment or from/to within script:</p> |
| 408 | <p>On ARM, the first 4 arguments will go into r0, r1, r2, and r3, in that order. |
| 409 | The remaining (if any) will go through stack.</p> |
| 410 | <p>For ext_vec_types such as float2, a set of registers will be used. In the case |
| 411 | of float2, a register pair will be used. Specifically, if float2 is the first |
| 412 | argument in the function prototype, float2.x will go into r0, and float2.y, |
| 413 | r1.</p> |
| 414 | <p>Note: stack will be aligned to the coarsest-grained argument. In the case of |
| 415 | float2 above as an argument, parameter stack will be aligned to an 8-byte |
| 416 | boundary (if the sizes of other arguments are no greater than 8.)</p> |
| 417 | </li> |
| 418 | <li><p class="first">Calls from/to a separate compilation unit: (E.g., calls to Execution |
| 419 | Environment if those runtime library callees are not compiled using LLVM.)</p> |
| 420 | <p>On ARM, we use hardfp. Note that double will be placed in a register pair.</p> |
| 421 | </li> |
| 422 | </ol> |
| 423 | </div> |
| 424 | </div> |
| 425 | </body> |
| 426 | </html> |