segmation fault occurs when many groups are used

[k-takata]

see: https://bugs.ruby-lang.org/issues/8716

WindowsとOS Xで検証しました。

• 再現手順 ruby 2.0.0p247 (2013-06-27) [x64-mingw32]

a="()"
(32767.times{a<<'()'}
eval "/#{a}/=~''"

• 再現手順 ruby 2.0.0p0 (2013-02-24 revision 39474) [x86_64-darwin12.2.1]

a="()"
(1<<21).times{a<<'()'}
eval "/#{a}/=~''"

regexec.c:match_at()で呼ばれるSTACK_INITがサイズを考慮せずにxallocaしているため、スタックオーバーフローしています。

[k-takata]

It seems that b9fba1d causes random crashes with multithread settings.

[k-takata]

Oops, still SEGV occurs.
There were two causes with this issue.

1. Using alloca() may cause stack overflow when allocating very large area. (Already fixed.)
2. Group number is managed by MemNumType which is short int. Thus, the number become negative if the number of group exceeds 32767. It may cause access errors. (Not fixed yet.)

Should Onigmo support more than 32767 groups?

[k-takata]

Now the maximum number of capture groups is explicitly limited to 32767 (ONIG_MAX_CAPTURE_GROUP_NUM).