From: Paul Eggert <eggert@cs.ucla.edu>
To: Stefan Monnier <monnier@iro.umontreal.ca>, emacs-devel@gnu.org
Subject: Re: Stack allocation of Lisp objects
Date: Thu, 09 Oct 2014 00:09:37 -0700 [thread overview]
Message-ID: <543634B1.7000601@cs.ucla.edu> (raw)
In-Reply-To: <jwvzjd6eyco.fsf-monnier+emacs@gnu.org>
Stefan Monnier wrote:
> Apparently there's an AUTO_STRING somewhere which we stick into a heap
> allocated cons cell.
A plausible scenario is that you got bitten by a GCC bug, where GCC ignores
___attribute__ ((aligned (8))) on your platform. At least, that's how I
reproduced the problem on x86. I filed a GCC bug report
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63495>.
If I'm right, the GCC bug cascaded into an Emacs portability bug: Emacs should
use stack-based strings only if stack-base cons also works, as otherwise
STACK_CONS could create a heap-based cons cell that points to a stack-based
string, the symptom you observed. I fixed that bug in Emacs trunk bzr 118080.
Because of this fix, Emacs no longer uses stack-based allocation on x86 + recent
GCC, which is a bit of a downer. It should still work with older GCC though,
and I expect the GCC folks will fix the bug in newer GCC at some point.
prev parent reply other threads:[~2014-10-09 7:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-09 3:11 Stack allocation of Lisp objects Stefan Monnier
2014-10-09 7:09 ` Paul Eggert [this message]
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