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List:       fedora-devel-list
Subject:    Re: Fedora 32 System-Wide Change proposal: Build Python 3 to statically link with libpython3.8.a for
From:       Miro_Hrončok <mhroncok () redhat ! com>
Date:       2019-11-15 13:18:40
Message-ID: 978a31b1-1ada-4e29-3284-5481aa2069f1 () redhat ! com
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On 15. 11. 19 13:24, Aleksandra Fedorova wrote:
> Hi
> 
> On Fri, Nov 15, 2019 at 10:22 AM Victor Stinner <vstinner@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.

Already working on it.

> 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.

Yes indeed.

-- 
Miro Hrončok
--
Phone: +420777974800
IRC: mhroncok
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