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Re: Alignment of Lisp_Subr

From: Gaute B Strokkenes
Subject: Re: Alignment of Lisp_Subr
Date: Sun, 16 Nov 2003 11:25:13 +0100
User-agent: Gnus/5.1003 (Gnus v5.10.3) Emacs/21.3.50 (gnu/linux)

On 14 nov 2003, address@hidden wrote:

>>>>>> "Gaute" == Gaute B Strokkenes <Gaute> writes:
> Gaute> On 13 nov 2003, address@hidden wrote:
>>> There may be issues with Lisp objects with tagbits at the
>>> bottom.  I know XEmacs had some problems on recent glibc, which
>>> were never properly diagnosed.  It's probable that this was due
>>> to excessive cleverness in optimizing space use of malloc
>>> blocks, but if you do run into weirdness (we were crashing)
>>> feel free to ping me and I'll dig up the thread.
> Gaute> Are you saying that glibc malloc does not return blocks
> Gaute> that are sufficiently aligned?  My copy of the glibc manual
> Gaute> says:
> No, I'm saying that XEmacs (which has had tagbits in the lower bits
> for a couple of years now) was crashing for unknown reasons.
> Wolfram Gloger thought it might have to do with tagbits in Lisp
> objects, but the bug was never identified.

Ah, sorry.  I read you as saying that glibc was "excessively clever"
with the way it managed memory, but on a second reading that's not
what you were saying at all.

As an aside, putting tagbits in the lowest order bits ought to make
it easier to use emacs with the Boehm GC (though I'm not sure that is
necessarily a great idea.)

Gaute Strokkenes                        http://www.srcf.ucam.org/~gs234/
I know how to do SPECIAL EFFECTS!!

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