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SUSPEND/GC bug: OPSYFT
- To: BUG-LISP at MIT-MC
- Subject: SUSPEND/GC bug: OPSYFT
- From: Jonathan A. Rees <JAR at MIT-MC>
- Date: Fri, 16 Oct 81 02:31:00 GMT
- Original-date: 15 October 1981 22:31-EDT
The location OPSYFT in list space is clobberred by the startup code
that gets run after a suspend happens. However, that list cell is
subject to garbage collection; if it can
get on the freelist (it can; don't ask me how - all I
know is that in Lisp 2088, on a Tops-20 at Yale, it has happened), the cell can get allocated for another use
before the SUSPEND, and clobberred after.
In our case it was the value word for a SUBR property in a PLIST;
the symptom was UNBOUND PC WITH ILLEGAL OPCODE or something of
Look at the code near TNXSET and the comments before and after TNXSET.