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http://bugs.exim.org/show_bug.cgi?id=1467
--- Comment #3 from Graycode <xgcode@???> 2014-04-16 19:09:12 ---
There is something more happening here beyond just honoring the
match_limit. The impact is an unbounded loop vs. just an
exponential search.
Consider the folling variants of the original expression:
\x22[a-z0-9$#^'\x22!?,(.|\n);:\s-]{20,80}\x22(.|\n){996,3000}$
\x22[a-z0-9'@#\s]{20,80}\x22(.|\n){996,3100}
\x22[a-z8-9@@@'####\s]{20,80}\x22(.|\n){996,997}
\x22[a-y8-9@@@'####\s]{20,80}\x22(.|\n){996,997}
\x22[a-z8-9@@@'####\s]{20,31}\x22(.|\n){996,997}
\w[a-z8-9@@@'####\s]{20,31}\x22(.|\w){996,997}
\x20[a-z8-9@@@'####\s]{20,31}\x22(.|\n){996,997}
\x20[a-y3-4@@@'####\s]{20,31}\x22(.|\n){996,997}
JIT appears to loop infinitely when used on the test data that was
provided (on my x86 PC).
Now change the 996 to any lesser value, such as 995, and those
expressions are then able to execute (and do so quickly).
Triggering the condition does seem to depend upon what is specified
in the [class] as well as other factors.
The issue appears to be more global than JIT. With the interpreter
Exec(), the above expressions reach even a 999 million match_limit
after about 1 minute crunching. But using a repetition of {995,997}
or {800,3000} or {995,} they execute properly in a few milliseconds.
Older PCRE versions also exhibit this same behavior, the oldest I
tried was 8.20.
Below is a DIFF of the output of "pcretest -d" (that shows PCRE's
internal compiled code) for these 2 expressions:
/\x20[a-y3-4@@@'####\s]{20,31}\x22(.|\n){995,997}/is
/\x20[a-y3-4@@@'####\s]{20,31}\x22(.|\n){996,997}/is
Again, the 995 runs fine but the 996 seems to loop unbounded.
I do not profess to understand it. It might be helpful to Philip or
Zoltan in case the compilation is different in their environments.
Highlight the 995 has codes that the 996 does not:
13975 Brazero
13976 32 Bra
And the 995 has an extra '32 Ket' to match the above '32 Bra'.
*** code_995.x Wed Apr 16 11:27:40 2014
--- code_996.x Wed Apr 16 11:28:12 2014
***************
*** 1,10 ****
PCRE version 8.35 2014-04-04
re> ------------------------------------------------------------------
! 0 14011 Bra
3 /i
5 [\x09-\x0d #'34@-Ya-y]{20,31}+
43 /i "
45 6 CBra 1
50 AllAny
51 5 Alt
--- 1,10 ----
PCRE version 8.35 2014-04-04
re> ------------------------------------------------------------------
! 0 14004 Bra
3 /i
5 [\x09-\x0d #'34@-Ya-y]{20,31}+
43 /i "
45 6 CBra 1
50 AllAny
51 5 Alt
***************
*** 4977,5004 ****
13958 11 Ket
13961 6 CBra 1
13966 AllAny
13967 5 Alt
13970 /i \x0a
13972 11 Ket
! 13975 Brazero
! 13976 32 Bra
! 13979 6 CBra 1
! 13984 AllAny
! 13985 5 Alt
! 13988 /i \x0a
! 13990 11 Ket
! 13993 Brazero
! 13994 6 CBra 1
! 13999 AllAny
! 14000 5 Alt
! 14003 /i \x0a
! 14005 11 Ket
! 14008 32 Ket
! 14011 14011 Ket
! 14014 End
------------------------------------------------------------------
Capturing subpattern count = 1
Contains explicit CR or LF match
Options: caseless dotall
First char = ' '
Need char = '"'
--- 4977,5001 ----
13958 11 Ket
13961 6 CBra 1
13966 AllAny
13967 5 Alt
13970 /i \x0a
13972 11 Ket
! 13975 6 CBra 1
! 13980 AllAny
! 13981 5 Alt
! 13984 /i \x0a
! 13986 11 Ket
! 13989 Brazero
! 13990 6 CBra 1
! 13995 AllAny
! 13996 5 Alt
! 13999 /i \x0a
! 14001 11 Ket
! 14004 14004 Ket
! 14007 End
------------------------------------------------------------------
Capturing subpattern count = 1
Contains explicit CR or LF match
Options: caseless dotall
First char = ' '
Need char = '"'
Regards,
Graycode
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