Unmaintained GCC/gfortran version is shipped

[fxcoudert]

On macOS, this repo currently ships gfortran and its libraries based on a modified version 11.3.0 https://github.com/isuruf/gcc/releases/tag/gcc-11.3.0-2

GCC 11 has reached EOL 6 months ago, so it seems like a good plan to upgrade to a newer version. I would be willing to help, if someone can clarify what the expectations are (I am a Homebrew and GCC maintainer).

[mattip]

We are working towards eliminating the use of the modified gfortran. So far we have refactored to use the native gfortran supplied with the github runner images, see #211. Unfortunately the move to the macos-15 image seems to have broken the build, see #219 and #223 to try to fix it. If you have any ideas why the build there is failing, we are all ears.

[mattip]

Is there a way to tell macOS to use a different compiler? I am not sure what we were using on the macos-13 builds before #211 ...

[fxcoudert]

“the native gfortran supplied with the github runner images” is gfortran/GCC provided by Homebrew. Several versions are available, see for example https://github.com/actions/runner-images/blob/main/images/macos/macos-15-arm64-Readme.md

I'm not sure that's suitable for your needs, but I may be misunderstanding the goal of this repo. Homebrew ships software built on every macOS major version, targeting this same macOS version. These versions are not suitable to deploy to earlier macOS versions. For example, on my laptop runnning macOS 26:

$ otool -l /opt/homebrew/opt/gcc/lib/gcc/current/libgfortran.5.dylib
[…]
Load command 10
      cmd LC_BUILD_VERSION
  cmdsize 32
 platform 1
    minos 26.0
      sdk 26.0
   ntools 1
     tool 3
  version 1221.4

means that this shared library can only run on 26 and later (that's the minos field). So that makes it unsuitable (I think) to distribute in wheels, which should run on a large variety of macOS versions.

The version provided for example in conda-forge is built specially for that purpose. See:

$ otool -l /Users/fx/miniforge3/pkgs/libgfortran5-15.2.0-h742603c_1/lib/libgfortran.5.dylib
[…]
Load command 9
      cmd LC_BUILD_VERSION
  cmdsize 32
 platform 1
    minos 11.0
      sdk 11.0
   ntools 1
     tool 3
  version 951.9

Now we have minos 11.0 which is the earliest macOS version that supports Apple Silicon, meaning essentially all macOS versions are supported. On x86_64, I think the conda-forge build targets 10.12.

It takes a different approach to building GCC to achieve that, see in what is done in conda-forge/gfortran_impl_osx-64-feedstock#94 for example.

---

I don't know the policy and relationships of the different python projects, but I feel you have two options at this stage:

• use an existing build of gcc/gfortran that is widely compatible, such as conda-forge's
• build your own version

[mattip]

The goal here is to build OpenBLAS to run on macos-10.9 and up for x86_64 and macos-11 and up for arm64, so it can be used by NumPy and SciPy for their wheels.

I guess we should explore using miniforge compilers