From: ts <decoux@...>
Date: 2004-08-31T23:59:11+09:00
Subject: Re: (Revised) [PATCH] Subtle bug in bignum.c

>>>>> "M" == Markus  <markus@reality.com> writes:

M> I've always thought (but remember, I don't really know C) that volatile
M> was a hint to the compiler that code that _used_ something should _not_
M> hold it in a register, because something else might modify it at any
M> time (e.g. the system clock).  So I am not sure why it would help.

 Yes, you are right.

 Now `x' and `y' will not be in a register, and ruby will find it on the
 stack if the GC is called in bignew() *even* if a new Bignum is created by
 rb_big_clone() and stored at this address.

 The initial problem is that the new Bignum (created by rb_big_clone()) was
 stored in a register (because `x' was in a register), then the content of
 the register was replaced with another variable (RBIGNUM(y)->digits) when
 the gc was called and this is why ruby was unable to mark the Bignum


Guy Decoux