My understanding is that the TLS model is entirely a performance optimisation; it does not change the symbol's visibility. Now, as per the only non-source documentation of the Linux ELF TLS ABI I can find¹, the all the thread-local symbols using the initial-exec model are required to be known at initial execution, as they're allocated in a static area that's only set up at initial load by the dynamic loader. This obviously doesn't work if you try to dlopen a binary containing symbols with the initial-exec TLS model.
Of course, this documentation is out of date, and libc has long had support for loading some initial-exec TLS symbols after initial program load - precisely for libGL, which wants both minimum overhead and a small number of TLS symbols. We had problems with this in Natty, where Mesa gained a dependency on libstdc++, which also has some TLS symbols, and was causing crashes with anything that tried to dlopen libGL and didn't already have a copy of libstdc++ in the program image. (That was bug 259219). Now, this was allegedly an underlying libc bug that's been fixed; I was under the impression that we'd dropped the tls patch when updating to mesa 8.0 in Precise. I'm now investigating whether we still need it. I don't believe that the TLS patch is to blame for JOGL's issues; I think it's more likely that it's exposing a race somewhere - a global- dynamic symbol requires a couple more instructions (and potentially extra memory accesses) to access, which would change the timing. ¹: http://www.akkadia.org/drepper/tls.pdf -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to mesa in Ubuntu. https://bugs.launchpad.net/bugs/965798 Title: Multithreaded tls_model("global-dynamic") glXMakeContextCurrent ___tls_get_addr () freeze/deadlock To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/mesa/+bug/965798/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp
