From: Paul Eggert <eggert@cs.ucla.edu>
To: Eli Zaretskii <eliz@gnu.org>
Cc: m43cap@yandex.com, herbert@mailbox.org, emacs-devel@gnu.org
Subject: Re: USE_LSB_TAG not supported on this platform
Date: Tue, 9 Feb 2016 09:37:15 -0800 [thread overview]
Message-ID: <56BA23CB.4070001@cs.ucla.edu> (raw)
In-Reply-To: <83bn7pddlu.fsf@gnu.org>
On 02/09/2016 08:59 AM, Eli Zaretskii wrote:
> Thanks. Out of curiosity: which hosts can behave like that?
16-bit PDP-11s running 7th Edition Unix. malloc returned only a multiple
of 2 there. :-)
I think there were 32-bit platforms where malloc returned only a
multiple of 4, but can't find any offhand now. For what it's worth,
glibc documents a minimum of 8, for all glibc platforms.
> Also, why are we sure that the loops will end at some point on those
> hosts? Shouldn't we perhaps set a limit to the loop iterations, to be
> sure we don't infloop there?
We're not absolutely sure. Certainly the C standard doesn't guarantee
it; malloc can return a pointer that is always odd, on weird platforms
where alignof always returns 1. I view this as almost purely theoretical
though, due to the practical performance benefit of alignment to at
least sizeof(double). It's conceivable (though very unlikely) that Emacs
will infloop on some truly oddball platform that does not care about
performance; but if that happens it'll be OK, as the infloop would
almost surely happen during a build and the builder would then send us a
bug report and we can deal with it then. I think adding a counter would
complicate the code (and possibly introduce bugs, in code that's never
really exercised) for not enough benefit.
next prev parent reply other threads:[~2016-02-09 17:37 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 8:32 USE_LSB_TAG not supported on this platform C. Baxter
2016-02-04 13:24 ` Stefan Monnier
2016-02-04 15:51 ` Paul Eggert
2016-02-04 22:29 ` Herbert J. Skuhra
2016-02-05 1:22 ` Paul Eggert
2016-02-05 9:45 ` Colin Baxter
2016-02-06 10:55 ` Herbert J. Skuhra
2016-02-06 16:04 ` Herbert J. Skuhra
2016-02-07 15:11 ` Wolfgang Jenkner
2016-02-07 19:14 ` Herbert J. Skuhra
2016-02-07 21:35 ` Herbert J. Skuhra
2016-02-08 19:45 ` Paul Eggert
2016-02-08 20:14 ` Eli Zaretskii
2016-02-09 8:39 ` Paul Eggert
2016-02-09 16:59 ` Eli Zaretskii
2016-02-09 17:37 ` Paul Eggert [this message]
2016-02-09 18:02 ` Eli Zaretskii
2016-02-10 19:29 ` Colin Baxter
2016-02-08 23:01 ` Herbert J. Skuhra
2016-02-09 1:10 ` Paul Eggert
2016-02-09 11:12 ` Herbert J. Skuhra
2016-02-09 23:37 ` Paul Eggert
2016-02-09 15:53 ` Wolfgang Jenkner
2016-02-09 23:33 ` Paul Eggert
2016-02-06 20:34 ` Paul Eggert
2016-02-07 16:52 ` Herbert J. Skuhra
2016-02-07 21:34 ` Paul Eggert
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