On 09/14/2015 08:29 AM, Florian Weimer wrote: > On 09/11/2015 04:34 PM, Carlos O'Donell wrote: > >>> How do you propose to resolve symbol conflicts if both the system >>> library and the bundled library are loaded into the same process? The >>> current ELF linking scheme lacks good support for bundling libraries >>> whose exported symbols have not been mangled in some way. > >> If you need different versions of the same shared libraries in the same >> process then you must use dlmopen to load the conflicting set into a >> distinct load namespace. >> >> At present dlmopen is not functional for this purpose in upstream >> glibc master. It is something that I'm working on fixing [1]. > > I looked at the Solaris documentation, and I'm not sure if it's the > right use-case. This seems to provide complete isolation, and would > break things like SQLite (at least older versions without file-private > locks) which need process-global state. Correct, with dlmopen you have complete isolation, but I don't understand the SQLite issue, so if you could expand on the requirement I'm happy to listen. > I think the real issue here is the ELF model with backwards/forwards > linking and symbol interposition. Ideally, we should load each DSO > exactly once, resolve object symbols only against explicit DT_NEEDED > dependencies (not indirect dependencies), and make most symbols > non-interposable by default. At least this is my gut feeling. This is > a very difficult problem, especially at distribution scale. I'm not sure how difficult this would be because I'm not sure how many symbols rely upon indirect dependencies. I think it would be a worthwhile cleanup to turn on something like you suggest, and attempt to bootstrap the OS using Fedora Bootstrap [1]. > We currently do not perform proper symbol namespace management in Fedora > (as we discussed before). Perhaps we should try to track DSO symbol > namespaces first, and use that data to guide further evolution of > dynamic linking. Agreed. We do indeed need some infrastructure in tools to extract all symbols out of the entire distribution and review them. Cheers, Carlos. [1] http://fedora-bootstrap.osop.rhcloud.com/ (currently down?) -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct
