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bug#23760: 25.0.95; emacs 25.0.95 doesn't build with glibc-2.23.90

From: Florian Weimer
Subject: bug#23760: 25.0.95; emacs 25.0.95 doesn't build with glibc-2.23.90
Date: Mon, 20 Jun 2016 10:48:19 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1

On 06/19/2016 05:02 AM, Paul Eggert wrote:
If I understand things correctly, the Emacs 'configure' script
discovered that the test glibc version did not declare and define a
symbol __malloc_initialize_hook, and so Emacs supplied its own
implementation of malloc, complete with __malloc_initialize_hook. Since
__malloc_initialize_hook was poisoned, this didn't work.

Yes, that's right. I didn't account for the possibility that Emacs would use symbols in the implementation namespace for implementing its own malloc.

I suppose Emacs could work around the problem by using
__malloc_initialize_hook when linked against an old glibc, and by using
a new symbol emacs_malloc_initialize_hook when linked against its
substitute implementation. Although this would insulate distant-future
versions of Emacs against the poisoning, it wouldn't work for Emacs 25
(the next Emacs version) and earlier; these systems would be unbuildable
with a glibc that poisons __malloc_initialize_hook. So as a practical
matter, aren't we better off having glibc simply not declare

You mean, not declare it in <malloc.h>?  I already posted a patch for that:


I'm more worried about the other __ variables in the Emacs malloc. Their in Emacs definition does not even match the one in glibc. The difference is probably harmless, but it is fairly close to be being broken.


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