1<html> 2<head> 3<title>pcre2jit specification</title> 4</head> 5<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6<h1>pcre2jit man page</h1> 7<p> 8Return to the <a href="index.html">PCRE2 index page</a>. 9</p> 10<p> 11This page is part of the PCRE2 HTML documentation. It was generated 12automatically from the original man page. If there is any nonsense in it, 13please consult the man page, in case the conversion went wrong. 14<br> 15<ul> 16<li><a name="TOC1" href="#SEC1">PCRE2 JUST-IN-TIME COMPILER SUPPORT</a> 17<li><a name="TOC2" href="#SEC2">AVAILABILITY OF JIT SUPPORT</a> 18<li><a name="TOC3" href="#SEC3">SIMPLE USE OF JIT</a> 19<li><a name="TOC4" href="#SEC4">MATCHING SUBJECTS CONTAINING INVALID UTF</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 MATCHING</a> 22<li><a name="TOC7" href="#SEC7">CONTROLLING THE JIT STACK</a> 23<li><a name="TOC8" href="#SEC8">JIT STACK FAQ</a> 24<li><a name="TOC9" href="#SEC9">FREEING JIT SPECULATIVE MEMORY</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">PCRE2 JUST-IN-TIME COMPILER SUPPORT</a><br> 32<P> 33Just-in-time compiling is a heavyweight optimization that can greatly speed up 34pattern matching. However, it comes at the cost of extra processing before the 35match is performed, so it is of most benefit when the same pattern is going to 36be matched many times. This does not necessarily mean many calls of a matching 37function; if the pattern is not anchored, matching attempts may take place many 38times at various positions in the subject, even for a single call. Therefore, 39if the subject string is very long, it may still pay to use JIT even for 40one-off matches. JIT support is available for all of the 8-bit, 16-bit and 4132-bit PCRE2 libraries. 42</P> 43<P> 44JIT support applies only to the traditional Perl-compatible matching function. 45It does not apply when the DFA matching function is being used. The code for 46JIT support was written by Zoltan Herczeg. 47</P> 48<br><a name="SEC2" href="#TOC1">AVAILABILITY OF JIT SUPPORT</a><br> 49<P> 50JIT support is an optional feature of PCRE2. The "configure" option 51--enable-jit (or equivalent CMake option) must be set when PCRE2 is built if 52you want to use JIT. The support is limited to the following hardware 53platforms: 54<pre> 55 ARM 32-bit (v7, and Thumb2) 56 ARM 64-bit 57 IBM s390x 64 bit 58 Intel x86 32-bit and 64-bit 59 LoongArch 64 bit 60 MIPS 32-bit and 64-bit 61 Power PC 32-bit and 64-bit 62 RISC-V 32-bit and 64-bit 63</pre> 64If --enable-jit is set on an unsupported platform, compilation fails. 65</P> 66<P> 67A client program can tell if JIT support is available by calling 68<b>pcre2_config()</b> with the PCRE2_CONFIG_JIT option. The result is one if 69PCRE2 was built with JIT support, and zero otherwise. However, having the JIT 70code available does not guarantee that it will be used for any particular 71match. One reason for this is that there are a number of options and pattern 72items that are 73<a href="#unsupported">not supported by JIT</a> 74(see below). Another reason is that in some environments JIT is unable to get 75memory in which to build its compiled code. The only guarantee from 76<b>pcre2_config()</b> is that if it returns zero, JIT will definitely <i>not</i> 77be used. 78</P> 79<P> 80A simple program does not need to check availability in order to use JIT when 81possible. The API is implemented in a way that falls back to the interpretive 82code if JIT is not available or cannot be used for a given match. For programs 83that need the best possible performance, there is a 84<a href="#fastpath">"fast path"</a> 85API that is JIT-specific. 86</P> 87<br><a name="SEC3" href="#TOC1">SIMPLE USE OF JIT</a><br> 88<P> 89To make use of the JIT support in the simplest way, all you have to do is to 90call <b>pcre2_jit_compile()</b> after successfully compiling a pattern with 91<b>pcre2_compile()</b>. This function has two arguments: the first is the 92compiled pattern pointer that was returned by <b>pcre2_compile()</b>, and the 93second is zero or more of the following option bits: PCRE2_JIT_COMPLETE, 94PCRE2_JIT_PARTIAL_HARD, or PCRE2_JIT_PARTIAL_SOFT. 95</P> 96<P> 97If JIT support is not available, a call to <b>pcre2_jit_compile()</b> does 98nothing and returns PCRE2_ERROR_JIT_BADOPTION. Otherwise, the compiled pattern 99is passed to the JIT compiler, which turns it into machine code that executes 100much faster than the normal interpretive code, but yields exactly the same 101results. The returned value from <b>pcre2_jit_compile()</b> is zero on success, 102or a negative error code. 103</P> 104<P> 105There is a limit to the size of pattern that JIT supports, imposed by the size 106of machine stack that it uses. The exact rules are not documented because they 107may change at any time, in particular, when new optimizations are introduced. 108If a pattern is too big, a call to <b>pcre2_jit_compile()</b> returns 109PCRE2_ERROR_NOMEMORY. 110</P> 111<P> 112PCRE2_JIT_COMPLETE requests the JIT compiler to generate code for complete 113matches. If you want to run partial matches using the PCRE2_PARTIAL_HARD or 114PCRE2_PARTIAL_SOFT options of <b>pcre2_match()</b>, you should set one or both 115of the other options as well as, or instead of PCRE2_JIT_COMPLETE. The JIT 116compiler generates different optimized code for each of the three modes 117(normal, soft partial, hard partial). When <b>pcre2_match()</b> is called, the 118appropriate code is run if it is available. Otherwise, the pattern is matched 119using interpretive code. 120</P> 121<P> 122You can call <b>pcre2_jit_compile()</b> multiple times for the same compiled 123pattern. It does nothing if it has previously compiled code for any of the 124option bits. For example, you can call it once with PCRE2_JIT_COMPLETE and 125(perhaps later, when you find you need partial matching) again with 126PCRE2_JIT_COMPLETE and PCRE2_JIT_PARTIAL_HARD. This time it will ignore 127PCRE2_JIT_COMPLETE and just compile code for partial matching. If 128<b>pcre2_jit_compile()</b> is called with no option bits set, it immediately 129returns zero. This is an alternative way of testing whether JIT is available. 130</P> 131<P> 132At present, it is not possible to free JIT compiled code except when the entire 133compiled pattern is freed by calling <b>pcre2_code_free()</b>. 134</P> 135<P> 136In some circumstances you may need to call additional functions. These are 137described in the section entitled 138<a href="#stackcontrol">"Controlling the JIT stack"</a> 139below. 140</P> 141<P> 142There are some <b>pcre2_match()</b> options that are not supported by JIT, and 143there are also some pattern items that JIT cannot handle. Details are given 144<a href="#unsupported">below.</a> 145In both cases, matching automatically falls back to the interpretive code. If 146you want to know whether JIT was actually used for a particular match, you 147should arrange for a JIT callback function to be set up as described in the 148section entitled 149<a href="#stackcontrol">"Controlling the JIT stack"</a> 150below, even if you do not need to supply a non-default JIT stack. Such a 151callback function is called whenever JIT code is about to be obeyed. If the 152match-time options are not right for JIT execution, the callback function is 153not obeyed. 154</P> 155<P> 156If the JIT compiler finds an unsupported item, no JIT data is generated. You 157can find out if JIT compilation was successful for a compiled pattern by 158calling <b>pcre2_pattern_info()</b> with the PCRE2_INFO_JITSIZE option. A 159non-zero result means that JIT compilation was successful. A result of 0 means 160that JIT support is not available, or the pattern was not processed by 161<b>pcre2_jit_compile()</b>, or the JIT compiler was not able to handle the 162pattern. Successful JIT compilation does not, however, guarantee the use of JIT 163at match time because there are some match time options that are not supported 164by JIT. 165</P> 166<br><a name="SEC4" href="#TOC1">MATCHING SUBJECTS CONTAINING INVALID UTF</a><br> 167<P> 168When a pattern is compiled with the PCRE2_UTF option, subject strings are 169normally expected to be a valid sequence of UTF code units. By default, this is 170checked at the start of matching and an error is generated if invalid UTF is 171detected. The PCRE2_NO_UTF_CHECK option can be passed to <b>pcre2_match()</b> to 172skip the check (for improved performance) if you are sure that a subject string 173is valid. If this option is used with an invalid string, the result is 174undefined. The calling program may crash or loop or otherwise misbehave. 175</P> 176<P> 177However, a way of running matches on strings that may contain invalid UTF 178sequences is available. Calling <b>pcre2_compile()</b> with the 179PCRE2_MATCH_INVALID_UTF option has two effects: it tells the interpreter in 180<b>pcre2_match()</b> to support invalid UTF, and, if <b>pcre2_jit_compile()</b> 181is subsequently called, the compiled JIT code also supports invalid UTF. 182Details of how this support works, in both the JIT and the interpretive cases, 183is given in the 184<a href="pcre2unicode.html"><b>pcre2unicode</b></a> 185documentation. 186</P> 187<P> 188There is also an obsolete option for <b>pcre2_jit_compile()</b> called 189PCRE2_JIT_INVALID_UTF, which currently exists only for backward compatibility. 190It is superseded by the <b>pcre2_compile()</b> option PCRE2_MATCH_INVALID_UTF 191and should no longer be used. It may be removed in future. 192<a name="unsupported"></a></P> 193<br><a name="SEC5" href="#TOC1">UNSUPPORTED OPTIONS AND PATTERN ITEMS</a><br> 194<P> 195The <b>pcre2_match()</b> options that are supported for JIT matching are 196PCRE2_COPY_MATCHED_SUBJECT, PCRE2_NOTBOL, PCRE2_NOTEOL, PCRE2_NOTEMPTY, 197PCRE2_NOTEMPTY_ATSTART, PCRE2_NO_UTF_CHECK, PCRE2_PARTIAL_HARD, and 198PCRE2_PARTIAL_SOFT. The PCRE2_ANCHORED and PCRE2_ENDANCHORED options are not 199supported at match time. 200</P> 201<P> 202If the PCRE2_NO_JIT option is passed to <b>pcre2_match()</b> it disables the 203use of JIT, forcing matching by the interpreter code. 204</P> 205<P> 206The only unsupported pattern items are \C (match a single data unit) when 207running in a UTF mode, and a callout immediately before an assertion condition 208in a conditional group. 209</P> 210<br><a name="SEC6" href="#TOC1">RETURN VALUES FROM JIT MATCHING</a><br> 211<P> 212When a pattern is matched using JIT, the return values are the same as those 213given by the interpretive <b>pcre2_match()</b> code, with the addition of one 214new error code: PCRE2_ERROR_JIT_STACKLIMIT. This means that the memory used for 215the JIT stack was insufficient. See 216<a href="#stackcontrol">"Controlling the JIT stack"</a> 217below for a discussion of JIT stack usage. 218</P> 219<P> 220The error code PCRE2_ERROR_MATCHLIMIT is returned by the JIT code if searching 221a very large pattern tree goes on for too long, as it is in the same 222circumstance when JIT is not used, but the details of exactly what is counted 223are not the same. The PCRE2_ERROR_DEPTHLIMIT error code is never returned 224when JIT matching is used. 225<a name="stackcontrol"></a></P> 226<br><a name="SEC7" href="#TOC1">CONTROLLING THE JIT STACK</a><br> 227<P> 228When the compiled JIT code runs, it needs a block of memory to use as a stack. 229By default, it uses 32KiB on the machine stack. However, some large or 230complicated patterns need more than this. The error PCRE2_ERROR_JIT_STACKLIMIT 231is given when there is not enough stack. Three functions are provided for 232managing blocks of memory for use as JIT stacks. There is further discussion 233about the use of JIT stacks in the section entitled 234<a href="#stackfaq">"JIT stack FAQ"</a> 235below. 236</P> 237<P> 238The <b>pcre2_jit_stack_create()</b> function creates a JIT stack. Its arguments 239are a starting size, a maximum size, and a general context (for memory 240allocation functions, or NULL for standard memory allocation). It returns a 241pointer to an opaque structure of type <b>pcre2_jit_stack</b>, or NULL if there 242is an error. The <b>pcre2_jit_stack_free()</b> function is used to free a stack 243that is no longer needed. If its argument is NULL, this function returns 244immediately, without doing anything. (For the technically minded: the address 245space is allocated by mmap or VirtualAlloc.) A maximum stack size of 512KiB to 2461MiB should be more than enough for any pattern. 247</P> 248<P> 249The <b>pcre2_jit_stack_assign()</b> function specifies which stack JIT code 250should use. Its arguments are as follows: 251<pre> 252 pcre2_match_context *mcontext 253 pcre2_jit_callback callback 254 void *data 255</pre> 256The first argument is a pointer to a match context. When this is subsequently 257passed to a matching function, its information determines which JIT stack is 258used. If this argument is NULL, the function returns immediately, without doing 259anything. There are three cases for the values of the other two options: 260<pre> 261 (1) If <i>callback</i> is NULL and <i>data</i> is NULL, an internal 32KiB block 262 on the machine stack is used. This is the default when a match 263 context is created. 264 265 (2) If <i>callback</i> is NULL and <i>data</i> is not NULL, <i>data</i> must be 266 a pointer to a valid JIT stack, the result of calling 267 <b>pcre2_jit_stack_create()</b>. 268 269 (3) If <i>callback</i> is not NULL, it must point to a function that is 270 called with <i>data</i> as an argument at the start of matching, in 271 order to set up a JIT stack. If the return from the callback 272 function is NULL, the internal 32KiB stack is used; otherwise the 273 return value must be a valid JIT stack, the result of calling 274 <b>pcre2_jit_stack_create()</b>. 275</pre> 276A callback function is obeyed whenever JIT code is about to be run; it is not 277obeyed when <b>pcre2_match()</b> is called with options that are incompatible 278for JIT matching. A callback function can therefore be used to determine 279whether a match operation was executed by JIT or by the interpreter. 280</P> 281<P> 282You may safely use the same JIT stack for more than one pattern (either by 283assigning directly or by callback), as long as the patterns are matched 284sequentially in the same thread. Currently, the only way to set up 285non-sequential matches in one thread is to use callouts: if a callout function 286starts another match, that match must use a different JIT stack to the one used 287for currently suspended match(es). 288</P> 289<P> 290In a multithread application, if you do not specify a JIT stack, or if you 291assign or pass back NULL from a callback, that is thread-safe, because each 292thread has its own machine stack. However, if you assign or pass back a 293non-NULL JIT stack, this must be a different stack for each thread so that the 294application is thread-safe. 295</P> 296<P> 297Strictly speaking, even more is allowed. You can assign the same non-NULL stack 298to a match context that is used by any number of patterns, as long as they are 299not used for matching by multiple threads at the same time. For example, you 300could use the same stack in all compiled patterns, with a global mutex in the 301callback to wait until the stack is available for use. However, this is an 302inefficient solution, and not recommended. 303</P> 304<P> 305This is a suggestion for how a multithreaded program that needs to set up 306non-default JIT stacks might operate: 307<pre> 308 During thread initialization 309 thread_local_var = pcre2_jit_stack_create(...) 310 311 During thread exit 312 pcre2_jit_stack_free(thread_local_var) 313 314 Use a one-line callback function 315 return thread_local_var 316</pre> 317All the functions described in this section do nothing if JIT is not available. 318<a name="stackfaq"></a></P> 319<br><a name="SEC8" href="#TOC1">JIT STACK FAQ</a><br> 320<P> 321(1) Why do we need JIT stacks? 322<br> 323<br> 324PCRE2 (and JIT) is a recursive, depth-first engine, so it needs a stack where 325the local data of the current node is pushed before checking its child nodes. 326Allocating real machine stack on some platforms is difficult. For example, the 327stack chain needs to be updated every time if we extend the stack on PowerPC. 328Although it is possible, its updating time overhead decreases performance. So 329we do the recursion in memory. 330</P> 331<P> 332(2) Why don't we simply allocate blocks of memory with <b>malloc()</b>? 333<br> 334<br> 335Modern operating systems have a nice feature: they can reserve an address space 336instead of allocating memory. We can safely allocate memory pages inside this 337address space, so the stack could grow without moving memory data (this is 338important because of pointers). Thus we can allocate 1MiB address space, and 339use only a single memory page (usually 4KiB) if that is enough. However, we can 340still grow up to 1MiB anytime if needed. 341</P> 342<P> 343(3) Who "owns" a JIT stack? 344<br> 345<br> 346The owner of the stack is the user program, not the JIT studied pattern or 347anything else. The user program must ensure that if a stack is being used by 348<b>pcre2_match()</b>, (that is, it is assigned to a match context that is passed 349to the pattern currently running), that stack must not be used by any other 350threads (to avoid overwriting the same memory area). The best practice for 351multithreaded programs is to allocate a stack for each thread, and return this 352stack through the JIT callback function. 353</P> 354<P> 355(4) When should a JIT stack be freed? 356<br> 357<br> 358You can free a JIT stack at any time, as long as it will not be used by 359<b>pcre2_match()</b> again. When you assign the stack to a match context, only a 360pointer is set. There is no reference counting or any other magic. You can free 361compiled patterns, contexts, and stacks in any order, anytime. 362Just <i>do not</i> call <b>pcre2_match()</b> with a match context pointing to an 363already freed stack, as that will cause SEGFAULT. (Also, do not free a stack 364currently used by <b>pcre2_match()</b> in another thread). You can also replace 365the stack in a context at any time when it is not in use. You should free the 366previous stack before assigning a replacement. 367</P> 368<P> 369(5) Should I allocate/free a stack every time before/after calling 370<b>pcre2_match()</b>? 371<br> 372<br> 373No, because this is too costly in terms of resources. However, you could 374implement some clever idea which release the stack if it is not used in let's 375say two minutes. The JIT callback can help to achieve this without keeping a 376list of patterns. 377</P> 378<P> 379(6) OK, the stack is for long term memory allocation. But what happens if a 380pattern causes stack overflow with a stack of 1MiB? Is that 1MiB kept until the 381stack is freed? 382<br> 383<br> 384Especially on embedded systems, it might be a good idea to release memory 385sometimes without freeing the stack. There is no API for this at the moment. 386Probably a function call which returns with the currently allocated memory for 387any stack and another which allows releasing memory (shrinking the stack) would 388be a good idea if someone needs this. 389</P> 390<P> 391(7) This is too much of a headache. Isn't there any better solution for JIT 392stack handling? 393<br> 394<br> 395No, thanks to Windows. If POSIX threads were used everywhere, we could throw 396out this complicated API. 397</P> 398<br><a name="SEC9" href="#TOC1">FREEING JIT SPECULATIVE MEMORY</a><br> 399<P> 400<b>void pcre2_jit_free_unused_memory(pcre2_general_context *<i>gcontext</i>);</b> 401</P> 402<P> 403The JIT executable allocator does not free all memory when it is possible. It 404expects new allocations, and keeps some free memory around to improve 405allocation speed. However, in low memory conditions, it might be better to free 406all possible memory. You can cause this to happen by calling 407pcre2_jit_free_unused_memory(). Its argument is a general context, for custom 408memory management, or NULL for standard memory management. 409</P> 410<br><a name="SEC10" href="#TOC1">EXAMPLE CODE</a><br> 411<P> 412This is a single-threaded example that specifies a JIT stack without using a 413callback. A real program should include error checking after all the function 414calls. 415<pre> 416 int rc; 417 pcre2_code *re; 418 pcre2_match_data *match_data; 419 pcre2_match_context *mcontext; 420 pcre2_jit_stack *jit_stack; 421 422 re = pcre2_compile(pattern, PCRE2_ZERO_TERMINATED, 0, 423 &errornumber, &erroffset, NULL); 424 rc = pcre2_jit_compile(re, PCRE2_JIT_COMPLETE); 425 mcontext = pcre2_match_context_create(NULL); 426 jit_stack = pcre2_jit_stack_create(32*1024, 512*1024, NULL); 427 pcre2_jit_stack_assign(mcontext, NULL, jit_stack); 428 match_data = pcre2_match_data_create(re, 10); 429 rc = pcre2_match(re, subject, length, 0, 0, match_data, mcontext); 430 /* Process result */ 431 432 pcre2_code_free(re); 433 pcre2_match_data_free(match_data); 434 pcre2_match_context_free(mcontext); 435 pcre2_jit_stack_free(jit_stack); 436 437<a name="fastpath"></a></PRE> 438</P> 439<br><a name="SEC11" href="#TOC1">JIT FAST PATH API</a><br> 440<P> 441Because the API described above falls back to interpreted matching when JIT is 442not available, it is convenient for programs that are written for general use 443in many environments. However, calling JIT via <b>pcre2_match()</b> does have a 444performance impact. Programs that are written for use where JIT is known to be 445available, and which need the best possible performance, can instead use a 446"fast path" API to call JIT matching directly instead of calling 447<b>pcre2_match()</b> (obviously only for patterns that have been successfully 448processed by <b>pcre2_jit_compile()</b>). 449</P> 450<P> 451The fast path function is called <b>pcre2_jit_match()</b>, and it takes exactly 452the same arguments as <b>pcre2_match()</b>. However, the subject string must be 453specified with a length; PCRE2_ZERO_TERMINATED is not supported. Unsupported 454option bits (for example, PCRE2_ANCHORED and PCRE2_ENDANCHORED) are ignored, as 455is the PCRE2_NO_JIT option. The return values are also the same as for 456<b>pcre2_match()</b>, plus PCRE2_ERROR_JIT_BADOPTION if a matching mode (partial 457or complete) is requested that was not compiled. 458</P> 459<P> 460When you call <b>pcre2_match()</b>, as well as testing for invalid options, a 461number of other sanity checks are performed on the arguments. For example, if 462the subject pointer is NULL but the length is non-zero, an immediate error is 463given. Also, unless PCRE2_NO_UTF_CHECK is set, a UTF subject string is tested 464for validity. In the interests of speed, these checks do not happen on the JIT 465fast path. If invalid UTF data is passed when PCRE2_MATCH_INVALID_UTF was not 466set for <b>pcre2_compile()</b>, the result is undefined. The program may crash 467or loop or give wrong results. In the absence of PCRE2_MATCH_INVALID_UTF you 468should call <b>pcre2_jit_match()</b> in UTF mode only if you are sure the 469subject is valid. 470</P> 471<P> 472Bypassing the sanity checks and the <b>pcre2_match()</b> wrapping can give 473speedups of more than 10%. 474</P> 475<br><a name="SEC12" href="#TOC1">SEE ALSO</a><br> 476<P> 477<b>pcre2api</b>(3), <b>pcre2unicode</b>(3) 478</P> 479<br><a name="SEC13" href="#TOC1">AUTHOR</a><br> 480<P> 481Philip Hazel (FAQ by Zoltan Herczeg) 482<br> 483Retired from University Computing Service 484<br> 485Cambridge, England. 486<br> 487</P> 488<br><a name="SEC14" href="#TOC1">REVISION</a><br> 489<P> 490Last updated: 21 February 2024 491<br> 492Copyright © 1997-2024 University of Cambridge. 493<br> 494<p> 495Return to the <a href="index.html">PCRE2 index page</a>. 496</p> 497