Hi On Fri, Nov 15, 2019 at 10:22 AM Victor Stinner <vstin...@redhat.com> wrote: > > Hi Jan, > > With the helper of Florian Weimer and Charalampos Stratakis, we also agreed > to test this flag in priority. I understood that it disables the LD_PRELOAD > feature: it's no longer possible to override symbols in libpython with > LD_PRELOAD. Thanks to that, the compiler can avoid PLT indirection for > function calls and can inline more function functions in libpython. I'm > talking about a function call from libpython to libpython: something which is > very common in python. Basically, almost all function calls are calls from > libpython to libpython. > > I'm impressed. Thanks to -fno-semantic-interposition, I get the same speedup > on a dynamically linked Python (libpython) compared to statically linked > Python! > > Yesterday, I tried on a vanilla Python compiled manually: > > ./configure --enable-optimizations --with-lto --enable-shared > CFLAGS="-fno-semantic-interposition" LDFLAGS="-fno-semantic-interposition" > > I saw the same speed up than avoiding --enable-shared. Today I validated this > result using the RPM generated by Charalampos's PR: > https://src.fedoraproject.org/rpms/python38/pull-request/53 > > In short, https://fedoraproject.org/wiki/Changes/PythonStaticSpeedup is > useless: there is no need to modify Python to statically link it to > libpython. We can keep the dynamically library libpython and keep Python > dynamically linked to it. We only need to pass -fno-semantic-interposition to > compiler and linker flags when building Python! > > I'm not sure if we need a Fedora change just for a compiler flag. Again, the > only drawback is that we will no longer be able to override a symbol using > LD_PRELOAD. Honestly, I never did that. I don't see any use case for that. > But I used LD_PRELOAD on the libc multiple times to mock the system clock for > example.
Please do file a Change. It works not only as a coordination tracker, but also as a tool to inform everyone about changes happening in Fedora. The discussion on the topic has been very interesting, as well as the outcome. I think it would be nice to see the summary with the estimated impact and highlight it via Release Notes. > If someone really needs LD_PRELOAD, it's quite easy to build a custom Python > without -fno-semantic-interposition. > > Victor > _______________________________________________ > devel mailing list -- devel@lists.fedoraproject.org > To unsubscribe send an email to devel-le...@lists.fedoraproject.org > Fedora Code of Conduct: > https://docs.fedoraproject.org/en-US/project/code-of-conduct/ > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines > List Archives: > https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org -- Aleksandra Fedorova bookwar _______________________________________________ devel mailing list -- devel@lists.fedoraproject.org To unsubscribe send an email to devel-le...@lists.fedoraproject.org Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org
