I'll betray my lack of understanding of how ABIs work: PEP 571 (manylinux2010) defines a set of libraries besides libc which compatible wheels can safely link against, such as glib and libXrender. Most of these are only versioned by the filename suffix (like .so.6), while glibc and a few presumably related pieces (CXXABI, GLIBCXX, GCC) are defined with specific versions (which are the maximum versions for compatible wheels, and the minimum for compatible platforms). If we move to manylinux tags based purely on the glibc version, what happens to the versions of all the other symbols and libraries? Do we just continue to build on some old version of CentOS and presume that it will work for any reasonably recent Linux distro? Are the other ABI symbol versions tied to the glibc version somehow? When, if ever, does auditwheel update its list of permissible libraries to link against? Do we lose the ability for a system to explicitly declare that it is or isn't compatible with a given manylinux variant (via the _manylinux? Presumably it would still require a new PEP, and changes to various tools, to allow manylinux wheels based around an alternative libc implementation? Is it worth naming these tags like manylinux_glibc_2_12, to anticipate that possibility? Or is that unnecessary verbosity? +1 to the overall idea of making it easier to move to new manylinux tags in the future, assuming we can do that without causing lots of compatibility problems. Thomas On Fri, Nov 30, 2018, at 8:09 AM, Nathaniel Smith wrote:
Hi all,
The manylinux1 -> manylinux2010 transition has turned out to be very difficult. Timeline so far:> March 2017: CentOS 5 went EOL April 2018: PEP 517 accepted May 2018: support for manylinux2010 lands in warehouse November 2018: support lands in auditwheel, and pip master December 2018: 21 months after CentOS 5 EOL, wwee still don't have an official build environment, or support in a pip release> We'll get through this, but it's been super painful and maybe we can change things somehow so it will suck less next time.> We don't have anything like this pain on Windows or macOS. We never have to update pip, warehouse, etc., after those OSes hit EOLs. Why not?> On Windows, we have just two tags: "win32" and "win_amd64". These are defined to mean something like "this wheel will run on any recent-ish Windows system". So the meaning of the tag actually changes over time: it used to be that if a wheel said it ran on win32, then that meant it would work on winxp, but since winxp hit EOL people started uploading "win32" wheels that don't work on winxp, and that's worked fine.> On macOS, the tags look like "macosx_10_9_x86_64". So here we have the OS version embedded in the tag. This means that we do occasionally switch which tags we're using, kind of like how manylinux1 -> manylinux2010 is intended to work. But, unlike for the manylinux tags, defining a new macosx tag is totally trivial: every time a new OS version is released, the tag springs into existence without any human intervention. Warehouse already accepts uploads with this tag; pip already knows which systems can install wheels with this tag, etc.> Can we take any inspiration from this for manylinux?
We could do the Windows thing, and have a plain "manylinux" tag that means "any recent-ish glibc-based Linux". Today it would be defined to be "any distro newer than CentOS 6". When CentOS 6 goes out of service, we could tweak the definition to be "any distro newer than CentOS 7". Most parts of the toolchain wouldn't need to be updated, though, because the tag wouldn't change, and by assumption, enforcement wouldn't really be needed, because the only people who could break would be ones running on unsupported platforms. Just like happens on Windows.> We could do the macOS thing, and have a "manylinux_${glibc version}" tag that means "this package works on any Linux using glibc newer than ${glibc version}". We're already using this as our heuristic to handle the current manylinux profiles, so e.g. manylinux1 is effectively equivalent to manylinux_2_5, and manylinux2010 will be equivalent to manylinux_2_12. That way we'd define the manylinux tags once, get support into pip and warehouse and auditwheel once, and then in the future the only thing that would have to change to support new distro releases or new architectures would be to set up a proper build environment.> What do y'all think?
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