Upgrade interpreter to match JIT in handling of nested pattern recursions

Author: PhilipHazel

ChangeLog

@@ -172,8 +172,12 @@ undefined behaviour.
 
 47. Refactor the handling of whole-pattern recursion (?0) in pcre2_match() so
 that its end is handled similarly to other recursions. This has altered the
-behaviour of   /|(?0)./endanchored   which was previously not right. However,
-it still differs from JIT.
+behaviour of   /|(?0)./endanchored   which was previously not right.
+
+48. Improved the test for looping recursion by checking the last referenced 
+character as well as the current character. This allows some patterns that 
+previously triggered the check to run to completion instead of giving the loop 
+error. 
 
 
 Version 10.42 11-December-2022

doc/html/pcre2compat.html

@@ -246,6 +246,12 @@ <h1>pcre2compat man page</h1>
 PCRE2_UTF and PCRE2_UCP will use similar rules to Perl's "/u"; something closer
 to "/a" could be selected by adding other PCRE2_EXTRA_ASCII* options on top.
 </P>
+<P>
+22. Some recursive patterns that Perl diagnoses as infinite recursions can be
+handled by PCRE2, either by the interpreter or the JIT. An example is
+/(?:|(?0)abcd)(?(R)|\z)/, which matches a sequence of any number of repeated
+"abcd" substrings at the end of the subject.
+</P>
 <br><b>
 AUTHOR
 </b><br>
@@ -261,7 +267,7 @@ <h1>pcre2compat man page</h1>
 REVISION
 </b><br>
 <P>
-Last updated: 12 October 2023
+Last updated: 30 November 2023
 <br>
 Copyright &copy; 1997-2023 University of Cambridge.
 <br>

doc/pcre2.txt

@@ -5256,6 +5256,11 @@ DIFFERENCES BETWEEN PCRE2 AND PERL
        to  Perl's  "/u";  something closer to "/a" could be selected by adding
        other PCRE2_EXTRA_ASCII* options on top.
 
+       22. Some recursive patterns that Perl diagnoses as infinite  recursions
+       can be handled by PCRE2, either by the interpreter or the JIT. An exam-
+       ple is /(?:|(?0)abcd)(?(R)|\z)/, which matches a sequence of any number
+       of repeated "abcd" substrings at the end of the subject.
+
 
 AUTHOR
 
@@ -5266,11 +5271,11 @@ AUTHOR
 
 REVISION
 
-       Last updated: 12 October 2023
+       Last updated: 30 November 2023
        Copyright (c) 1997-2023 University of Cambridge.
 
 
-PCRE2 10.43                    19 September 2023                PCRE2COMPAT(3)
+PCRE2 10.43                    30 November 2023                 PCRE2COMPAT(3)
 ------------------------------------------------------------------------------
 
 

doc/pcre2compat.3

@@ -1,4 +1,4 @@
-.TH PCRE2COMPAT 3 "19 September 2023" "PCRE2 10.43"
+.TH PCRE2COMPAT 3 "30 November 2023" "PCRE2 10.43"
 .SH NAME
 PCRE2 - Perl-compatible regular expressions (revised API)
 .SH "DIFFERENCES BETWEEN PCRE2 AND PERL"
@@ -210,6 +210,11 @@ fall into any stack-overflow limit. PCRE2 made a similar change at release
 to set characters by context just like Perl's "/d". A regular expression using
 PCRE2_UTF and PCRE2_UCP will use similar rules to Perl's "/u"; something closer
 to "/a" could be selected by adding other PCRE2_EXTRA_ASCII* options on top.
+.P
+22. Some recursive patterns that Perl diagnoses as infinite recursions can be
+handled by PCRE2, either by the interpreter or the JIT. An example is
+/(?:|(?0)abcd)(?(R)|\ez)/, which matches a sequence of any number of repeated
+"abcd" substrings at the end of the subject.
 .
 .
 .SH AUTHOR
@@ -226,6 +231,6 @@ Cambridge, England.
 .rs
 .sp
 .nf
-Last updated: 12 October 2023
+Last updated: 30 November 2023
 Copyright (c) 1997-2023 University of Cambridge.
 .fi

doc/pcre2demo.3

@@ -1,4 +1,4 @@
-.TH PCRE2DEMO 3 "24 November 2023" "PCRE2 10.43-DEV"
+.TH PCRE2DEMO 3 "30 November 2023" "PCRE2 10.43-DEV"
 .\"AUTOMATICALLY GENERATED BY PrepareRelease - do not EDIT!
 .SH NAME
 // - A demonstration C program for PCRE2 - //

maint/README

@@ -448,12 +448,9 @@ years.
   gigabyte memory, but perhaps another implementation might be considered.
   Needs coordination between the interpreters and JIT.
 
-. There are regular requests for variable-length lookbehinds. An implementation
-  exists but is missing JIT support.
-
 . See also any suggestions in the GitHub issues.
 
 Philip Hazel
 Email local part: Philip.Hazel
 Email domain: gmail.com
-Last updated: 30 September 2023
+Last updated: 30 November 2023

src/pcre2_dfa_match.c

@@ -2913,7 +2913,6 @@ for (;;)
         int *local_workspace;
         PCRE2_SIZE *local_offsets;
         RWS_anchor *rws = (RWS_anchor *)RWS;
-        dfa_recursion_info *ri;
         PCRE2_SPTR callpat = start_code + GET(code, 1);
         uint32_t recno = (callpat == mb->start_code)? 0 :
           GET2(callpat, 1 + LINK_SIZE);
@@ -2930,18 +2929,24 @@ for (;;)
         rws->free -= RWS_RSIZE + RWS_OVEC_RSIZE;
 
         /* Check for repeating a recursion without advancing the subject
-        pointer. This should catch convoluted mutual recursions. (Some simple
-        cases are caught at compile time.) */
+        pointer or last used character. This should catch convoluted mutual
+        recursions. (Some simple cases are caught at compile time.) */
 
-        for (ri = mb->recursive; ri != NULL; ri = ri->prevrec)
-          if (recno == ri->group_num && ptr == ri->subject_position)
+        for (dfa_recursion_info *ri = mb->recursive;
+             ri != NULL;
+             ri = ri->prevrec)
+          {
+          if (recno == ri->group_num && ptr == ri->subject_position &&
+              mb->last_used_ptr == ri->last_used_ptr)
             return PCRE2_ERROR_RECURSELOOP;
+          }
 
         /* Remember this recursion and where we started it so as to
         catch infinite loops. */
 
         new_recursive.group_num = recno;
         new_recursive.subject_position = ptr;
+        new_recursive.last_used_ptr = mb->last_used_ptr;
         new_recursive.prevrec = mb->recursive;
         mb->recursive = &new_recursive;
 
@@ -4015,7 +4020,7 @@ for (;;)
       }
     match_data->subject_length = length;
     match_data->leftchar = (PCRE2_SIZE)(mb->start_used_ptr - subject);
-    match_data->rightchar = (PCRE2_SIZE)( mb->last_used_ptr - subject);
+    match_data->rightchar = (PCRE2_SIZE)(mb->last_used_ptr - subject);
     match_data->startchar = (PCRE2_SIZE)(start_match - subject);
     match_data->rc = rc;
 

src/pcre2_intmodedep.h

@@ -677,8 +677,8 @@ typedef struct pcre2_real_match_data {
 
 #ifndef PCRE2_PCRE2TEST
 
-/* Structures for checking for mutual recursion when scanning compiled or
-parsed code. */
+/* Structures for checking for mutual function recursion when scanning compiled
+or parsed code. */
 
 typedef struct recurse_check {
   struct recurse_check *prev;
@@ -690,7 +690,7 @@ typedef struct parsed_recurse_check {
   uint32_t *groupptr;
 } parsed_recurse_check;
 
-/* Structure for building a cache when filling in recursion offsets. */
+/* Structure for building a cache when filling in pattern recursion offsets. */
 
 typedef struct recurse_cache {
   PCRE2_SPTR group;
@@ -757,7 +757,7 @@ typedef struct compile_block {
   int  max_lookbehind;             /* Maximum lookbehind encountered (characters) */
   BOOL had_accept;                 /* (*ACCEPT) encountered */
   BOOL had_pruneorskip;            /* (*PRUNE) or (*SKIP) encountered */
-  BOOL had_recurse;                /* Had a recursion or subroutine call */
+  BOOL had_recurse;                /* Had a pattern recursion or subroutine call */
   BOOL dupnames;                   /* Duplicate names exist */
 } compile_block;
 
@@ -775,6 +775,7 @@ call within the pattern when running pcre2_dfa_match(). */
 typedef struct dfa_recursion_info {
   struct dfa_recursion_info *prevrec;
   PCRE2_SPTR subject_position;
+  PCRE2_SPTR last_used_ptr;
   uint32_t group_num;
 } dfa_recursion_info;
 
@@ -795,7 +796,7 @@ typedef struct heapframe {
   PCRE2_SIZE length;         /* Used for character, string, or code lengths */
   PCRE2_SIZE back_frame;     /* Amount to subtract on RRETURN */
   PCRE2_SIZE temp_size;      /* Used for short-term PCRE2_SIZE values */
-  uint32_t rdepth;           /* "Recursion" depth */
+  uint32_t rdepth;           /* Function "recursion" depth within pcre2_match() */
   uint32_t group_frame_type; /* Type information for group frames */
   uint32_t temp_32[4];       /* Used for short-term 32-bit or BOOL values */
   uint8_t return_id;         /* Where to go on in internal "return" */
@@ -828,14 +829,15 @@ typedef struct heapframe {
   allows for exactly the right size ovector for the number of capturing
   parentheses. (See also the comment for pcre2_real_match_data above.) */
 
-  PCRE2_SPTR eptr;           /* MUST BE FIRST */
-  PCRE2_SPTR start_match;    /* Can be adjusted by \K */
-  PCRE2_SPTR mark;           /* Most recent mark on the success path */
-  uint32_t current_recurse;  /* Current (deepest) recursion number */
-  uint32_t capture_last;     /* Most recent capture */
-  PCRE2_SIZE last_group_offset;  /* Saved offset to most recent group frame */
-  PCRE2_SIZE offset_top;     /* Offset after highest capture */
-  PCRE2_SIZE ovector[131072]; /* Must be last in the structure */
+  PCRE2_SPTR eptr;              /* MUST BE FIRST */
+  PCRE2_SPTR start_match;       /* Can be adjusted by \K */
+  PCRE2_SPTR mark;              /* Most recent mark on the success path */
+  PCRE2_SPTR recurse_last_used; /* Last character used at time of pattern recursion */
+  uint32_t current_recurse;     /* Group number of current (deepest) pattern recursion */
+  uint32_t capture_last;        /* Most recent capture */
+  PCRE2_SIZE last_group_offset; /* Saved offset to most recent group frame */
+  PCRE2_SIZE offset_top;        /* Offset after highest capture */
+  PCRE2_SIZE ovector[131072];   /* Must be last in the structure */
 } heapframe;
 
 /* This typedef is a check that the size of the heapframe structure is a
@@ -877,7 +879,7 @@ typedef struct match_block {
   uint16_t name_count;            /* Number of names in name table */
   uint16_t name_entry_size;       /* Size of entry in names table */
   PCRE2_SPTR name_table;          /* Table of group names */
-  PCRE2_SPTR start_code;          /* For use when recursing */
+  PCRE2_SPTR start_code;          /* For use in pattern recursion */
   PCRE2_SPTR start_subject;       /* Start of the subject string */
   PCRE2_SPTR check_subject;       /* Where UTF-checked from */
   PCRE2_SPTR end_subject;         /* Usable end of the subject string */
@@ -889,7 +891,7 @@ typedef struct match_block {
   PCRE2_SPTR nomatch_mark;        /* Mark pointer to pass back on failure */
   PCRE2_SPTR verb_ecode_ptr;      /* For passing back info */
   PCRE2_SPTR verb_skip_ptr;       /* For passing back a (*SKIP) name */
-  uint32_t verb_current_recurse;  /* Current recurse when (*VERB) happens */
+  uint32_t verb_current_recurse;  /* Current recursion group when (*VERB) happens */
   uint32_t moptions;              /* Match options */
   uint32_t poptions;              /* Pattern options */
   uint32_t skip_arg_count;        /* For counting SKIP_ARGs */
@@ -929,7 +931,7 @@ typedef struct dfa_match_block {
   pcre2_callout_block *cb;        /* Points to a callout block */
   void *callout_data;             /* To pass back to callouts */
   int (*callout)(pcre2_callout_block *,void *);  /* Callout function or NULL */
-  dfa_recursion_info *recursive;  /* Linked list of recursion data */
+  dfa_recursion_info *recursive;  /* Linked list of pattern recursion data */
 } dfa_match_block;
 
 #endif  /* PCRE2_PCRE2TEST */

src/pcre2_match.c

@@ -5383,9 +5383,11 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
 
 
     /* ===================================================================== */
-    /* Recursion either matches the current regex, or some subexpression. The
-    offset data is the offset to the starting bracket from the start of the
-    whole pattern. (This is so that it works from duplicated subpatterns.) */
+    /* Pattern recursion either matches the current regex, or some
+    subexpression. The offset data is the offset to the starting bracket from
+    the start of the whole pattern. This is so that it works from duplicated
+    subpatterns. For a whole-pattern recursion, we have to infer the number
+    zero. */
 
 #define Lframe_type F->temp_32[0]
 #define Lstart_branch F->temp_sptr[0]
@@ -5394,9 +5396,10 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
     bracode = mb->start_code + GET(Fecode, 1);
     number = (bracode == mb->start_code)? 0 : GET2(bracode, 1 + LINK_SIZE);
 
-    /* If we are already in a recursion, check for repeating the same one
-    without advancing the subject pointer. This should catch convoluted mutual
-    recursions. (Some simple cases are caught at compile time.) */
+    /* If we are already in a pattern recursion, check for repeating the same
+    one without changing the subject pointer or the last referenced character
+    in the subject. This should catch convoluted mutual recursions. (Some
+    simple cases are caught at compile time.) */
 
     if (Fcurrent_recurse != RECURSE_UNSET)
       {
@@ -5407,15 +5410,18 @@ fprintf(stderr, "++ %2ld op=%3d %s\n", Fecode - mb->start_code, *Fecode,
         P = (heapframe *)((char *)N - frame_size);
         if (N->group_frame_type == (GF_RECURSE | number))
           {
-          if (Feptr == P->eptr) return PCRE2_ERROR_RECURSELOOP;
+          if (Feptr == P->eptr && mb->last_used_ptr == P->recurse_last_used)
+            return PCRE2_ERROR_RECURSELOOP;
           break;
           }
         offset = P->last_group_offset;
         }
       }
 
-    /* Now run the recursion, branch by branch. */
+    /* Remember the current last referenced character and then run the
+    recursion branch by branch. */
 
+    F->recurse_last_used = mb->last_used_ptr;
     Lstart_branch = bracode;
     Lframe_type = GF_RECURSE | number;
 

testdata/testinput1

@@ -6648,4 +6648,7 @@ $/x
     a[]b
     (a)(?(1)a|b|c)
 
+/^..A(*SKIP)B|C/
+    12ADC
+
 # End of testinput1