Annotation of embedaddon/pcre/doc/html/pcrejit.html, revision 1.1.1.4
1.1 misho 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>
1.1.1.4 ! misho 17: <li><a name="TOC2" href="#SEC2">8-BIT, 16-BIT AND 32-BIT SUPPORT</a>
1.1.1.2 misho 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>
1.1.1.4 ! misho 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>
1.1 misho 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
1.1.1.2 misho 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>
1.1.1.4 ! misho 47: <br><a name="SEC2" href="#TOC1">8-BIT, 16-BIT AND 32-BIT SUPPORT</a><br>
1.1.1.2 misho 48: <P>
1.1.1.4 ! misho 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>).
1.1 misho 56: </P>
1.1.1.2 misho 57: <br><a name="SEC3" href="#TOC1">AVAILABILITY OF JIT SUPPORT</a><br>
1.1 misho 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
1.1.1.2 misho 66: Power PC 32-bit and 64-bit
1.1.1.4 ! misho 67: SPARC 32-bit (experimental)
1.1 misho 68: </pre>
1.1.1.3 misho 69: If --enable-jit is set on an unsupported platform, compilation fails.
1.1 misho 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
1.1.1.4 ! misho 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.
1.1 misho 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>
1.1.1.2 misho 86: <br><a name="SEC4" href="#TOC1">SIMPLE USE OF JIT</a><br>
1.1 misho 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
1.1.1.4 ! misho 95: no longer needed, instead of just freeing it yourself. This ensures that
! 96: any JIT data is also freed.
1.1 misho 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>
1.1.1.3 misho 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>
1.1 misho 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>
1.1.1.3 misho 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.
1.1 misho 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
1.1.1.3 misho 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.
1.1 misho 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
1.1.1.3 misho 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.
1.1 misho 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>
1.1.1.2 misho 167: <br><a name="SEC5" href="#TOC1">UNSUPPORTED OPTIONS AND PATTERN ITEMS</a><br>
1.1 misho 168: <P>
169: The only <b>pcre_exec()</b> options that are supported for JIT execution are
1.1.1.4 ! misho 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.
1.1 misho 173: </P>
174: <P>
1.1.1.4 ! misho 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.
1.1 misho 178: </P>
1.1.1.2 misho 179: <br><a name="SEC6" href="#TOC1">RETURN VALUES FROM JIT EXECUTION</a><br>
1.1 misho 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>
1.1.1.2 misho 197: <br><a name="SEC7" href="#TOC1">SAVING AND RESTORING COMPILED PATTERNS</a><br>
1.1 misho 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>
1.1.1.2 misho 210: <br><a name="SEC8" href="#TOC1">CONTROLLING THE JIT STACK</a><br>
1.1 misho 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
1.1.1.3 misho 243: PCRE_STUDY_JIT_COMPILE etc. There are three cases for the values of the other
244: two options:
1.1 misho 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:
1.1.1.3 misho 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>.
1.1 misho 258: </pre>
1.1.1.3 misho 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.
1.1 misho 272: </P>
273: <P>
1.1.1.3 misho 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
1.1 misho 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
1.1.1.3 misho 278: stack is available for use. However, this is an inefficient solution, and not
279: recommended.
1.1 misho 280: </P>
281: <P>
1.1.1.3 misho 282: This is a suggestion for how a multithreaded program that needs to set up
283: non-default JIT stacks might operate:
1.1 misho 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
1.1.1.3 misho 297: successful study with PCRE_STUDY_JIT_COMPILE etc.
1.1 misho 298: <a name="stackfaq"></a></P>
1.1.1.2 misho 299: <br><a name="SEC9" href="#TOC1">JIT STACK FAQ</a><br>
1.1 misho 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
1.1.1.4 ! misho 354: say two minutes. The JIT callback can help to achieve this without keeping a
1.1 misho 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>
1.1.1.3 misho 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.
1.1 misho 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>
1.1.1.2 misho 377: <br><a name="SEC10" href="#TOC1">EXAMPLE CODE</a><br>
1.1 misho 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>
1.1.1.4 ! misho 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>
1.1 misho 432: <P>
433: <b>pcreapi</b>(3)
434: </P>
1.1.1.4 ! misho 435: <br><a name="SEC13" href="#TOC1">AUTHOR</a><br>
1.1 misho 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>
1.1.1.4 ! misho 444: <br><a name="SEC14" href="#TOC1">REVISION</a><br>
1.1 misho 445: <P>
1.1.1.4 ! misho 446: Last updated: 17 March 2013
1.1 misho 447: <br>
1.1.1.4 ! misho 448: Copyright © 1997-2013 University of Cambridge.
1.1 misho 449: <br>
450: <p>
451: Return to the <a href="index.html">PCRE index page</a>.
452: </p>
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