Handling of a stack overflow during GC?

Hi,

I am currently working on improving the code handling call stack overflow
in my Common Lisp environment MKCL (http://common-lisp.net/project/mkcl/).
MKCL uses a somewhat older (7.2a4) version of the Boehm conservative GC.

I would like to know what would happen if a stack overflow were to occur during
a GC call/collection? The GC code seems to replace the SIGSEGV handler at
some point, will this new SIGSEGV handler still use the alternate signal
stack that MKCL has setup?

Also, as a side question, do you have an estimate of the stack depth
requirements of the GC?  It seems to be at least twice the usual
value of PTHREAD_STACK_MIN (which happens to be 16k on Linux).

Thanks for your help,

Jean-Claude Beaudoin