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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