Comment by rcxdude

3 days ago

>glibc has an unstable ABI, making back-portability impossible

Of all the libraries to call out for this, glibc is not the one. It's basically the only library on linux that actually has a strong commitment to providing a stable ABI, with its own symbol versioning system to allow it. It is a bit of a PITA to compile for an older version of that ABI, but it's very possible to be compatible with glibc across a wide range of versions and distributions (I don't know why there isn't a flag to do it: the most widely supported option is compiling on a system with the oldest glibc you want to support, and there's some header hacks which claim to be able to avoid that).

It's everything else necessary to interact with the system (especially anything desktop/multimedia) that's wildly unstable.

7 comments

rcxdude

delta_p_delta_x 3 days ago

Fair response.

I singled it out because I've been badly burnt by it in the past, and I dislike how it works compared to Win32. Back-targeting old glibc from newer (a very common case because developers tend to have newer distros than their users), requires either changes in source code (not build code, which is where it ought to be) to explicitly pin versions, or the ridiculousness of firing up an entire Docker container just for old glibc. It has regularly caused issues for things like Steam on Linux.

LtWorf 3 days ago
If you build on random developer's machines rather than a unified build environment you've already failed at so many things that the glibc problem is certainly not your biggest concern.
- rcxdude 3 days ago
  
  Regardless it's still a PITA to maintain an ancient distro as a build environment and the alternatives are hacky. It might be the best of the linux libraries but it's still not good.
  
  1 reply →

M95D 3 days ago

All I can say is that Gentoo specifically forbids downgrading glibc. I think it's the only package where they did this. [1] The .ebuild is full of patches and workarounds.

[1] See line 873. https://github.com/gentoo/gentoo/blob/master/sys-libs/glibc/...

rcxdude 3 days ago

Yeah, that's forwards-compatibility, which is different. Something built targeting a newer version of glibc is unlikely to work with an older one. (and gentoo will by default build against the latest you have installed, so yeah, downgrading has a good chance of breaking near everything).

simoncion 3 days ago

> All I can say is that Gentoo specifically forbids downgrading glibc.

Nope. You're protected from accidentally doing it, not forbidden. Look:

  # I_ALLOW_TO_BREAK_MY_SYSTEM=yes emerge -1v =sys-libs/glibc-2.43-r4
  These are the packages that would be merged, in order:
  <snip>
  [ebuild     UD ] sys-libs/glibc-2.43-r4:2.2::gentoo [2.44-r3:2.2::gentoo] <snip>

  Total: 1 package (1 downgrade), Size of downloads: 0 KiB

  >>> Verifying ebuild manifests
  
  >>> Running pre-merge checks for sys-libs/glibc-2.43-r4
  
  >>> Emerging (1 of 1) sys-libs/glibc-2.43-r4::gentoo
   * glibc-2.43.tar.xz BLAKE2B SHA512 size ;-) ...           [ ok ]
   * glibc-2.43-patches-5.tar.xz BLAKE2B SHA512 size ;-) ... [ ok ]
   * Checking whether python3_14 is suitable ...
   *   dev-lang/python:3.14 ...                              [ ok ]
   * Using python3.14 to build (via PYTHON_COMPAT iteration)
  >>> Unpacking source...
   * Checking general environment sanity.
   * Sanity check to keep you from breaking your system:
   *  Downgrading glibc is not supported and a sure way to destruction.
   * Performing simple compile test for ABI=amd64 ...
   <snip>

If you don't set that environment variable, the downgrade blows up at the "Sanity check to keep you from breaking your system:" step with a message that includes a call stack that pretty much tells you how to override the safety check:

  * Call stack:
  *     ebuild.sh, line  143:  Called src_unpack
  *   environment, line 3570:  Called sanity_prechecks
  *   environment, line 3199:  Called die
  * The specific snippet of code:
  *               [[ ${I_ALLOW_TO_BREAK_MY_SYSTEM} = yes ]] || die "Aborting to save your system.";