bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Paul Eggert]

On 5/29/20 10:54 PM, Eli Zaretskii wrote:
> >    (USE_LSB_TAG
> >     ? (uintptr_t) word % GCALIGNMENT == Lisp_Symbol
> >     : (uintptr_t) word % alignof (struct Lisp_Symbol) == 0)
> I don't understand how this will work, given that Lisp object on the
> stack can be pushed as 2 non-contiguous 32-bit words.  Can you
> explain?

On a --with-wide-int host where !USE_LSB_TAG, the above test will work 
correctly on the low-order word of a Lisp object that is a symbol, 
because ((uintptr_t) word % alignof (struct Lisp_Symbol) == 0) must be 
true on such a word.

The test is only for symbols; it's not for other Lisp objects.