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

[Daniel Mendler]

On 3/10/23 13:13, Eli Zaretskii wrote:
>> 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!

Why not? There won't be a performance cost.