bug#62009: 29.0.60; Emacs crashes on setf symbol-name

[Eli Zaretskii]

> Date: Fri, 10 Mar 2023 12:36:17 +0100
> Cc: Gregory Heytings <gregory@heytings.org>,
>  Philip Kaludercic <philipk@posteo.net>, michael_heerdegen@web.de,
>  monnier@iro.umontreal.ca, 62009@debbugs.gnu.org, Eli Zaretskii
>  <eliz@gnu.org>, Augusto Stoffel <arstoffel@gmail.com>
> From: Daniel Mendler <mail@daniel-mendler.de>
> 
> >       /* Number of characters in string; MSB is used as the mark bit.  */
> >       ptrdiff_t size;
> >       /* If nonnegative, number of bytes in the string (which is multibyte).
> >      If negative, the string is unibyte:
> >      -1 for data normally allocated
> >      -2 for data in rodata (C string constants)
> >      -3 for data that must be immovable (used for bytecode)  */
> >       ptrdiff_t size_byte;
> 
> Thanks! That's good. Given that a read only flag already exists, it is
> easy to fix the issue. We just have to make sure that the size is
> negative for the symbol names and add a check in `aset`.

Let's not do that!