GNU bug report logs - #30855
25.3; temacs fails with bus error during garbage collection

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Message #34 received at 30855-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Ulrich Mueller <ulm <at> gentoo.org>, Eli Zaretskii <eliz <at> gnu.org>
Cc: schwab <at> suse.de, gentoo-bug <at> opensource.sf-tec.de, 30855-done <at> debbugs.gnu.org
Subject: Re: bug#30855: 25.3; temacs fails with bus error during garbage
 collection
Date: Tue, 20 Mar 2018 14:42:15 -0700

On 03/20/2018 02:19 PM, Ulrich Mueller wrote:
> Also, doesn't this bug affect other architectures too, and at least
> cause a performance penalty for unaligned access?

It might cause crashes on other (presumably less-common) architectures, 
which is worrisome.

The performance penalty is not something we'd want to worry about in the 
emacs-26 branch, since we don't want to assume that the compiler is 
storing Lisp words on fast-aligned boundaries; this is why we're using 
alignof instead of __alignof__. So the patch does not address the issue 
of optimizing for compilers that use only fast-aligned Lisp words (and I 
doubt whether it's worth worrying about, even in the master branch).

Although 32-bit sparc64 is rare compared to x86-64, I wouldn't consider 
it to be "extremely rare" in an absolute sense (at least, not for the 
next several years; ask me again after 2038 :-). Perhaps I'm biased by 
the fact that one of our department's production servers is still 
regularly used that way, but whatever. I backported the patch to the 
emacs-26 branch and am closing Bug#30855.

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