ABI limitation on the size of a class

[Christian BRUEL]

I'm trying to understand the rational for the 1.2 Limit section in the 
itanium C++ ABI (http://www.codesourcery.com/cxx-abi/abi.html#limits)

The section says that this limitation is due to RTTI implementation. Is 
it because of the field to the beginning of the complete type in the 
typeinfos ?
in the libstdc++ sources (gcc 3.3.3) this field ("whole_object" field) 
has type ptrdiff_t so the only limitation I can find in the size of an 
object is 2**31 bytes for a 32 bit machine.

The raisons should hide elsewhere, but I really don't see...

thank you,

  Christian