1 <html> 2 <head> 3 <title>pcrejit specification</title> 4 </head> 5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6 <h1>pcrejit man page</h1> 7 <p> 8 Return to the <a href="index.html">PCRE index page</a>. 9 </p> 10 <p> 11 This page is part of the PCRE HTML documentation. It was generated automatically 12 from the original man page. If there is any nonsense in it, please consult the 13 man page, in case the conversion went wrong. 14 <br> 15 <ul> 16 <li><a name="TOC1" href="#SEC1">PCRE JUST-IN-TIME COMPILER SUPPORT</a> 17 <li><a name="TOC2" href="#SEC2">8-BIT, 16-BIT AND 32-BIT SUPPORT</a> 18 <li><a name="TOC3" href="#SEC3">AVAILABILITY OF JIT SUPPORT</a> 19 <li><a name="TOC4" href="#SEC4">SIMPLE USE OF JIT</a> 20 <li><a name="TOC5" href="#SEC5">UNSUPPORTED OPTIONS AND PATTERN ITEMS</a> 21 <li><a name="TOC6" href="#SEC6">RETURN VALUES FROM JIT EXECUTION</a> 22 <li><a name="TOC7" href="#SEC7">SAVING AND RESTORING COMPILED PATTERNS</a> 23 <li><a name="TOC8" href="#SEC8">CONTROLLING THE JIT STACK</a> 24 <li><a name="TOC9" href="#SEC9">JIT STACK FAQ</a> 25 <li><a name="TOC10" href="#SEC10">EXAMPLE CODE</a> 26 <li><a name="TOC11" href="#SEC11">JIT FAST PATH API</a> 27 <li><a name="TOC12" href="#SEC12">SEE ALSO</a> 28 <li><a name="TOC13" href="#SEC13">AUTHOR</a> 29 <li><a name="TOC14" href="#SEC14">REVISION</a> 30 </ul> 31 <br><a name="SEC1" href="#TOC1">PCRE JUST-IN-TIME COMPILER SUPPORT</a><br> 32 <P> 33 Just-in-time compiling is a heavyweight optimization that can greatly speed up 34 pattern matching. However, it comes at the cost of extra processing before the 35 match is performed. Therefore, it is of most benefit when the same pattern is 36 going to be matched many times. This does not necessarily mean many calls of a 37 matching function; if the pattern is not anchored, matching attempts may take 38 place many times at various positions in the subject, even for a single call. 39 Therefore, if the subject string is very long, it may still pay to use JIT for 40 one-off matches. 41 </P> 42 <P> 43 JIT support applies only to the traditional Perl-compatible matching function. 44 It does not apply when the DFA matching function is being used. The code for 45 this support was written by Zoltan Herczeg. 46 </P> 47 <br><a name="SEC2" href="#TOC1">8-BIT, 16-BIT AND 32-BIT SUPPORT</a><br> 48 <P> 49 JIT support is available for all of the 8-bit, 16-bit and 32-bit PCRE 50 libraries. To keep this documentation simple, only the 8-bit interface is 51 described in what follows. If you are using the 16-bit library, substitute the 52 16-bit functions and 16-bit structures (for example, <i>pcre16_jit_stack</i> 53 instead of <i>pcre_jit_stack</i>). If you are using the 32-bit library, 54 substitute the 32-bit functions and 32-bit structures (for example, 55 <i>pcre32_jit_stack</i> instead of <i>pcre_jit_stack</i>). 56 </P> 57 <br><a name="SEC3" href="#TOC1">AVAILABILITY OF JIT SUPPORT</a><br> 58 <P> 59 JIT support is an optional feature of PCRE. The "configure" option --enable-jit 60 (or equivalent CMake option) must be set when PCRE is built if you want to use 61 JIT. The support is limited to the following hardware platforms: 62 <pre> 63 ARM v5, v7, and Thumb2 64 Intel x86 32-bit and 64-bit 65 MIPS 32-bit 66 Power PC 32-bit and 64-bit 67 SPARC 32-bit (experimental) 68 </pre> 69 If --enable-jit is set on an unsupported platform, compilation fails. 70 </P> 71 <P> 72 A program that is linked with PCRE 8.20 or later can tell if JIT support is 73 available by calling <b>pcre_config()</b> with the PCRE_CONFIG_JIT option. The 74 result is 1 when JIT is available, and 0 otherwise. However, a simple program 75 does not need to check this in order to use JIT. The normal API is implemented 76 in a way that falls back to the interpretive code if JIT is not available. For 77 programs that need the best possible performance, there is also a "fast path" 78 API that is JIT-specific. 79 </P> 80 <P> 81 If your program may sometimes be linked with versions of PCRE that are older 82 than 8.20, but you want to use JIT when it is available, you can test 83 the values of PCRE_MAJOR and PCRE_MINOR, or the existence of a JIT macro such 84 as PCRE_CONFIG_JIT, for compile-time control of your code. 85 </P> 86 <br><a name="SEC4" href="#TOC1">SIMPLE USE OF JIT</a><br> 87 <P> 88 You have to do two things to make use of the JIT support in the simplest way: 89 <pre> 90 (1) Call <b>pcre_study()</b> with the PCRE_STUDY_JIT_COMPILE option for 91 each compiled pattern, and pass the resulting <b>pcre_extra</b> block to 92 <b>pcre_exec()</b>. 93 94 (2) Use <b>pcre_free_study()</b> to free the <b>pcre_extra</b> block when it is 95 no longer needed, instead of just freeing it yourself. This ensures that 96 any JIT data is also freed. 97 </pre> 98 For a program that may be linked with pre-8.20 versions of PCRE, you can insert 99 <pre> 100 #ifndef PCRE_STUDY_JIT_COMPILE 101 #define PCRE_STUDY_JIT_COMPILE 0 102 #endif 103 </pre> 104 so that no option is passed to <b>pcre_study()</b>, and then use something like 105 this to free the study data: 106 <pre> 107 #ifdef PCRE_CONFIG_JIT 108 pcre_free_study(study_ptr); 109 #else 110 pcre_free(study_ptr); 111 #endif 112 </pre> 113 PCRE_STUDY_JIT_COMPILE requests the JIT compiler to generate code for complete 114 matches. If you want to run partial matches using the PCRE_PARTIAL_HARD or 115 PCRE_PARTIAL_SOFT options of <b>pcre_exec()</b>, you should set one or both of 116 the following options in addition to, or instead of, PCRE_STUDY_JIT_COMPILE 117 when you call <b>pcre_study()</b>: 118 <pre> 119 PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE 120 PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE 121 </pre> 122 The JIT compiler generates different optimized code for each of the three 123 modes (normal, soft partial, hard partial). When <b>pcre_exec()</b> is called, 124 the appropriate code is run if it is available. Otherwise, the pattern is 125 matched using interpretive code. 126 </P> 127 <P> 128 In some circumstances you may need to call additional functions. These are 129 described in the section entitled 130 <a href="#stackcontrol">"Controlling the JIT stack"</a> 131 below. 132 </P> 133 <P> 134 If JIT support is not available, PCRE_STUDY_JIT_COMPILE etc. are ignored, and 135 no JIT data is created. Otherwise, the compiled pattern is passed to the JIT 136 compiler, which turns it into machine code that executes much faster than the 137 normal interpretive code. When <b>pcre_exec()</b> is passed a <b>pcre_extra</b> 138 block containing a pointer to JIT code of the appropriate mode (normal or 139 hard/soft partial), it obeys that code instead of running the interpreter. The 140 result is identical, but the compiled JIT code runs much faster. 141 </P> 142 <P> 143 There are some <b>pcre_exec()</b> options that are not supported for JIT 144 execution. There are also some pattern items that JIT cannot handle. Details 145 are given below. In both cases, execution automatically falls back to the 146 interpretive code. If you want to know whether JIT was actually used for a 147 particular match, you should arrange for a JIT callback function to be set up 148 as described in the section entitled 149 <a href="#stackcontrol">"Controlling the JIT stack"</a> 150 below, even if you do not need to supply a non-default JIT stack. Such a 151 callback function is called whenever JIT code is about to be obeyed. If the 152 execution options are not right for JIT execution, the callback function is not 153 obeyed. 154 </P> 155 <P> 156 If the JIT compiler finds an unsupported item, no JIT data is generated. You 157 can find out if JIT execution is available after studying a pattern by calling 158 <b>pcre_fullinfo()</b> with the PCRE_INFO_JIT option. A result of 1 means that 159 JIT compilation was successful. A result of 0 means that JIT support is not 160 available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE etc., or 161 the JIT compiler was not able to handle the pattern. 162 </P> 163 <P> 164 Once a pattern has been studied, with or without JIT, it can be used as many 165 times as you like for matching different subject strings. 166 </P> 167 <br><a name="SEC5" href="#TOC1">UNSUPPORTED OPTIONS AND PATTERN ITEMS</a><br> 168 <P> 169 The only <b>pcre_exec()</b> options that are supported for JIT execution are 170 PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK, PCRE_NO_UTF32_CHECK, PCRE_NOTBOL, 171 PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and 172 PCRE_PARTIAL_SOFT. 173 </P> 174 <P> 175 The only unsupported pattern items are \C (match a single data unit) when 176 running in a UTF mode, and a callout immediately before an assertion condition 177 in a conditional group. 178 </P> 179 <br><a name="SEC6" href="#TOC1">RETURN VALUES FROM JIT EXECUTION</a><br> 180 <P> 181 When a pattern is matched using JIT execution, the return values are the same 182 as those given by the interpretive <b>pcre_exec()</b> code, with the addition of 183 one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used 184 for the JIT stack was insufficient. See 185 <a href="#stackcontrol">"Controlling the JIT stack"</a> 186 below for a discussion of JIT stack usage. For compatibility with the 187 interpretive <b>pcre_exec()</b> code, no more than two-thirds of the 188 <i>ovector</i> argument is used for passing back captured substrings. 189 </P> 190 <P> 191 The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a 192 very large pattern tree goes on for too long, as it is in the same circumstance 193 when JIT is not used, but the details of exactly what is counted are not the 194 same. The PCRE_ERROR_RECURSIONLIMIT error code is never returned by JIT 195 execution. 196 </P> 197 <br><a name="SEC7" href="#TOC1">SAVING AND RESTORING COMPILED PATTERNS</a><br> 198 <P> 199 The code that is generated by the JIT compiler is architecture-specific, and is 200 also position dependent. For those reasons it cannot be saved (in a file or 201 database) and restored later like the bytecode and other data of a compiled 202 pattern. Saving and restoring compiled patterns is not something many people 203 do. More detail about this facility is given in the 204 <a href="pcreprecompile.html"><b>pcreprecompile</b></a> 205 documentation. It should be possible to run <b>pcre_study()</b> on a saved and 206 restored pattern, and thereby recreate the JIT data, but because JIT 207 compilation uses significant resources, it is probably not worth doing this; 208 you might as well recompile the original pattern. 209 <a name="stackcontrol"></a></P> 210 <br><a name="SEC8" href="#TOC1">CONTROLLING THE JIT STACK</a><br> 211 <P> 212 When the compiled JIT code runs, it needs a block of memory to use as a stack. 213 By default, it uses 32K on the machine stack. However, some large or 214 complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT 215 is given when there is not enough stack. Three functions are provided for 216 managing blocks of memory for use as JIT stacks. There is further discussion 217 about the use of JIT stacks in the section entitled 218 <a href="#stackcontrol">"JIT stack FAQ"</a> 219 below. 220 </P> 221 <P> 222 The <b>pcre_jit_stack_alloc()</b> function creates a JIT stack. Its arguments 223 are a starting size and a maximum size, and it returns a pointer to an opaque 224 structure of type <b>pcre_jit_stack</b>, or NULL if there is an error. The 225 <b>pcre_jit_stack_free()</b> function can be used to free a stack that is no 226 longer needed. (For the technically minded: the address space is allocated by 227 mmap or VirtualAlloc.) 228 </P> 229 <P> 230 JIT uses far less memory for recursion than the interpretive code, 231 and a maximum stack size of 512K to 1M should be more than enough for any 232 pattern. 233 </P> 234 <P> 235 The <b>pcre_assign_jit_stack()</b> function specifies which stack JIT code 236 should use. Its arguments are as follows: 237 <pre> 238 pcre_extra *extra 239 pcre_jit_callback callback 240 void *data 241 </pre> 242 The <i>extra</i> argument must be the result of studying a pattern with 243 PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the other 244 two options: 245 <pre> 246 (1) If <i>callback</i> is NULL and <i>data</i> is NULL, an internal 32K block 247 on the machine stack is used. 248 249 (2) If <i>callback</i> is NULL and <i>data</i> is not NULL, <i>data</i> must be 250 a valid JIT stack, the result of calling <b>pcre_jit_stack_alloc()</b>. 251 252 (3) If <i>callback</i> is not NULL, it must point to a function that is 253 called with <i>data</i> as an argument at the start of matching, in 254 order to set up a JIT stack. If the return from the callback 255 function is NULL, the internal 32K stack is used; otherwise the 256 return value must be a valid JIT stack, the result of calling 257 <b>pcre_jit_stack_alloc()</b>. 258 </pre> 259 A callback function is obeyed whenever JIT code is about to be run; it is not 260 obeyed when <b>pcre_exec()</b> is called with options that are incompatible for 261 JIT execution. A callback function can therefore be used to determine whether a 262 match operation was executed by JIT or by the interpreter. 263 </P> 264 <P> 265 You may safely use the same JIT stack for more than one pattern (either by 266 assigning directly or by callback), as long as the patterns are all matched 267 sequentially in the same thread. In a multithread application, if you do not 268 specify a JIT stack, or if you assign or pass back NULL from a callback, that 269 is thread-safe, because each thread has its own machine stack. However, if you 270 assign or pass back a non-NULL JIT stack, this must be a different stack for 271 each thread so that the application is thread-safe. 272 </P> 273 <P> 274 Strictly speaking, even more is allowed. You can assign the same non-NULL stack 275 to any number of patterns as long as they are not used for matching by multiple 276 threads at the same time. For example, you can assign the same stack to all 277 compiled patterns, and use a global mutex in the callback to wait until the 278 stack is available for use. However, this is an inefficient solution, and not 279 recommended. 280 </P> 281 <P> 282 This is a suggestion for how a multithreaded program that needs to set up 283 non-default JIT stacks might operate: 284 <pre> 285 During thread initalization 286 thread_local_var = pcre_jit_stack_alloc(...) 287 288 During thread exit 289 pcre_jit_stack_free(thread_local_var) 290 291 Use a one-line callback function 292 return thread_local_var 293 </pre> 294 All the functions described in this section do nothing if JIT is not available, 295 and <b>pcre_assign_jit_stack()</b> does nothing unless the <b>extra</b> argument 296 is non-NULL and points to a <b>pcre_extra</b> block that is the result of a 297 successful study with PCRE_STUDY_JIT_COMPILE etc. 298 <a name="stackfaq"></a></P> 299 <br><a name="SEC9" href="#TOC1">JIT STACK FAQ</a><br> 300 <P> 301 (1) Why do we need JIT stacks? 302 <br> 303 <br> 304 PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack where 305 the local data of the current node is pushed before checking its child nodes. 306 Allocating real machine stack on some platforms is difficult. For example, the 307 stack chain needs to be updated every time if we extend the stack on PowerPC. 308 Although it is possible, its updating time overhead decreases performance. So 309 we do the recursion in memory. 310 </P> 311 <P> 312 (2) Why don't we simply allocate blocks of memory with <b>malloc()</b>? 313 <br> 314 <br> 315 Modern operating systems have a nice feature: they can reserve an address space 316 instead of allocating memory. We can safely allocate memory pages inside this 317 address space, so the stack could grow without moving memory data (this is 318 important because of pointers). Thus we can allocate 1M address space, and use 319 only a single memory page (usually 4K) if that is enough. However, we can still 320 grow up to 1M anytime if needed. 321 </P> 322 <P> 323 (3) Who "owns" a JIT stack? 324 <br> 325 <br> 326 The owner of the stack is the user program, not the JIT studied pattern or 327 anything else. The user program must ensure that if a stack is used by 328 <b>pcre_exec()</b>, (that is, it is assigned to the pattern currently running), 329 that stack must not be used by any other threads (to avoid overwriting the same 330 memory area). The best practice for multithreaded programs is to allocate a 331 stack for each thread, and return this stack through the JIT callback function. 332 </P> 333 <P> 334 (4) When should a JIT stack be freed? 335 <br> 336 <br> 337 You can free a JIT stack at any time, as long as it will not be used by 338 <b>pcre_exec()</b> again. When you assign the stack to a pattern, only a pointer 339 is set. There is no reference counting or any other magic. You can free the 340 patterns and stacks in any order, anytime. Just <i>do not</i> call 341 <b>pcre_exec()</b> with a pattern pointing to an already freed stack, as that 342 will cause SEGFAULT. (Also, do not free a stack currently used by 343 <b>pcre_exec()</b> in another thread). You can also replace the stack for a 344 pattern at any time. You can even free the previous stack before assigning a 345 replacement. 346 </P> 347 <P> 348 (5) Should I allocate/free a stack every time before/after calling 349 <b>pcre_exec()</b>? 350 <br> 351 <br> 352 No, because this is too costly in terms of resources. However, you could 353 implement some clever idea which release the stack if it is not used in let's 354 say two minutes. The JIT callback can help to achieve this without keeping a 355 list of the currently JIT studied patterns. 356 </P> 357 <P> 358 (6) OK, the stack is for long term memory allocation. But what happens if a 359 pattern causes stack overflow with a stack of 1M? Is that 1M kept until the 360 stack is freed? 361 <br> 362 <br> 363 Especially on embedded sytems, it might be a good idea to release memory 364 sometimes without freeing the stack. There is no API for this at the moment. 365 Probably a function call which returns with the currently allocated memory for 366 any stack and another which allows releasing memory (shrinking the stack) would 367 be a good idea if someone needs this. 368 </P> 369 <P> 370 (7) This is too much of a headache. Isn't there any better solution for JIT 371 stack handling? 372 <br> 373 <br> 374 No, thanks to Windows. If POSIX threads were used everywhere, we could throw 375 out this complicated API. 376 </P> 377 <br><a name="SEC10" href="#TOC1">EXAMPLE CODE</a><br> 378 <P> 379 This is a single-threaded example that specifies a JIT stack without using a 380 callback. 381 <pre> 382 int rc; 383 int ovector[30]; 384 pcre *re; 385 pcre_extra *extra; 386 pcre_jit_stack *jit_stack; 387 388 re = pcre_compile(pattern, 0, &error, &erroffset, NULL); 389 /* Check for errors */ 390 extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error); 391 jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024); 392 /* Check for error (NULL) */ 393 pcre_assign_jit_stack(extra, NULL, jit_stack); 394 rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30); 395 /* Check results */ 396 pcre_free(re); 397 pcre_free_study(extra); 398 pcre_jit_stack_free(jit_stack); 399 400 </PRE> 401 </P> 402 <br><a name="SEC11" href="#TOC1">JIT FAST PATH API</a><br> 403 <P> 404 Because the API described above falls back to interpreted execution when JIT is 405 not available, it is convenient for programs that are written for general use 406 in many environments. However, calling JIT via <b>pcre_exec()</b> does have a 407 performance impact. Programs that are written for use where JIT is known to be 408 available, and which need the best possible performance, can instead use a 409 "fast path" API to call JIT execution directly instead of calling 410 <b>pcre_exec()</b> (obviously only for patterns that have been successfully 411 studied by JIT). 412 </P> 413 <P> 414 The fast path function is called <b>pcre_jit_exec()</b>, and it takes exactly 415 the same arguments as <b>pcre_exec()</b>, plus one additional argument that 416 must point to a JIT stack. The JIT stack arrangements described above do not 417 apply. The return values are the same as for <b>pcre_exec()</b>. 418 </P> 419 <P> 420 When you call <b>pcre_exec()</b>, as well as testing for invalid options, a 421 number of other sanity checks are performed on the arguments. For example, if 422 the subject pointer is NULL, or its length is negative, an immediate error is 423 given. Also, unless PCRE_NO_UTF[8|16|32] is set, a UTF subject string is tested 424 for validity. In the interests of speed, these checks do not happen on the JIT 425 fast path, and if invalid data is passed, the result is undefined. 426 </P> 427 <P> 428 Bypassing the sanity checks and the <b>pcre_exec()</b> wrapping can give 429 speedups of more than 10%. 430 </P> 431 <br><a name="SEC12" href="#TOC1">SEE ALSO</a><br> 432 <P> 433 <b>pcreapi</b>(3) 434 </P> 435 <br><a name="SEC13" href="#TOC1">AUTHOR</a><br> 436 <P> 437 Philip Hazel (FAQ by Zoltan Herczeg) 438 <br> 439 University Computing Service 440 <br> 441 Cambridge CB2 3QH, England. 442 <br> 443 </P> 444 <br><a name="SEC14" href="#TOC1">REVISION</a><br> 445 <P> 446 Last updated: 17 March 2013 447 <br> 448 Copyright © 1997-2013 University of Cambridge. 449 <br> 450 <p> 451 Return to the <a href="index.html">PCRE index page</a>. 452 </p> 453