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

From: Eli Zaretskii <[email-masked]>
Date: Tue, 07 Mar 2023 19:39:51 +0200

> Cc: Stefan Monnier <[email-masked]>, [email-masked]
> Date: Tue, 7 Mar 2023 18:08:43 +0100
> From: Daniel Mendler <[email-masked]>
> 
> On 3/7/23 16:45, Michael Heerdegen wrote:
> > Daniel Mendler <[email-masked]> writes:
> > 
> >> Execute the following in the scratch buffer:
> >>
> >> (setf (aref (symbol-name 'car) 1) ?o)
> >>
> >> Emacs crashes with a segmentation fault. Is this a well-known issue? I
> >> could reproduce the problem on Emacs 27 and 29. Should there be some
> >> mechanism to protect the strings of symbols?
> >
> > Maybe the outcome was something like that we can't protect everybody in
> > every case from shooting in the own foot, I don't recall.
> 
> Maybe it would be possible to introduce a flag which marks strings as
> "frozen"? Then we could ensure that no mutations of such frozen string
> happen.

AFAICT, they _are_ frozen.  These names are in read-only memory, where
you cannot write.  That's why Emacs crashes, AFAIU: the code is trying
to write to protected memory.

Just don't do that, cause it's gonna hurt...