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Message-ID: <20170104105108.GD6695@port70.net>
Date: Wed, 4 Jan 2017 11:51:09 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: Reviving planned ldso changes
* Rich Felker <dalias@...c.org> [2017-01-03 00:43:51 -0500]:
> One item that's been on the agenda for a long time (maybe 1.5 years
> now?) is planned dynamic linker improvements. The thread "Further
> dynamic linker optimizations" from summer 2015 covered parts but maybe
> not all of what I had in mind.
>
> - Instead of a global flag for each library, have a separate linked
> list for globally visible libraries. This will speed up symbol
> lookup (by skipping non-global ones, and skipping checking the
> global flag) and also makes it so that load order searching can be
> done based on the order in which the libraries became global, rather
> than their original load order when they might have been non-global.
>
> - Dependency-order ctor execution. I think the walk order looks
> something like, starting at a given node (initially the main app or
> new library being loaded dynamically), traversing to its first
> deps[] entry that hasn't been constructed, or, if none remain,
> executing its ctors then traversing back to its needed_by. This
> process avoids the need for any call recursion and should be
> near-optimal (if not optimal) provided the position in a dso's
> deps[] list is saved in the dso struct.
>
> - Recursive dlopen improvements. The thread "dlopen deadlock" from
> January 2016 covers some of the issues. I don't think we reached a
> complete conclusion/solution, but for reasonable cases where it's
> clear that dlopen *should* work without deadlock, I think we have a
> proposed design that works.
>
> - Possibly other optimizations I've left out...
- symbol lookup logic is duplicated between do_dlsym and find_sym,
it would be nice to do that with common code path if possible.
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