[ft-devel] endless loops in bytecode (Re: Freetype-devel Digest, Vol 140, Issue 6)

[Hin-Tak Leung]

 Date: Sat, 10 Sep 2016 19:38:39 +0200 (CEST)
 From: Werner LEMBERG <address@hidden>
 To: address@hidden
 Subject: [ft-devel] endless loops in bytecode

> My only idea up to date is to count JMPR, JROT, and JROF
 separately,
 using a threshold of, say, 10000.  Those instructions
 are very rare in
 normal bytecode, and having so much jumps within a single
 function is
 extremely unlikely.
 
 
What about recording the offset of the last or last few jumps? That has the 
same-ish overhead as counting; and doesn't catch specially crafted fonts which 
jumps between #locations more than you record, but may be slightly better than 
just counting? i.e. if your last jump is from the same location, but you are 
not in an explicit loop like LOOPCALL ?