garbage colleciton crash

["Brett Bibby" <research@...>]

Hello,
We have been chasing a really bizarre bug all day. Undoubtedly it is in our code and not Lua, but I''m hoping someone familiar with the Lua garbage collector could help me understand the likely cause so I can try and find the bug in our code. We crash in either one of two places (lua 5).

call to lua_setgcthreshold(L,0)
Crash A call stack:
>luaC_collectgarbage
>luaC_sweep
>sweeplist
>freeobj
>luaH_free
>luaM_realloc
>free (crashes in here in the pool manager of MSL by Metrowerks)

call to lua_setgcthreshold(L,0)
Crash B call stack:
>luaC_collectgarbage
>mark
>propagatemarks
>traversetable (crashes on line 181: if(!ttisnil(gval(n))) and n is NULL after working down from index 510 to 0)

Here is the funny thing. I can get rid of the bug by slowly eliminating lines of lua source code until I can get it down to a single ascii character is the reason for the crash. For example, I can find the spot where:

test = 1 -- this will crash

I remove _one_ single ascii character from _anywhere_ in the file so the file is simply one byte shorter...

tes = 1 -- this won't crash
tst = 1 -- this won't crash either
tsts = 1 -- now it crashes again

I checked the chunk reader and everything and it works fine with hundreds of lines of scripts, functions, tables, etc.  I also have many MB of free RAM available and I tried malloc'ing a huge block after the non-crash one and that works fine too.  Is there any tips on debugging the gc anybody could share?

Thanks,
Brett