Over at https://github.com/python-pillow/Pillow, we switched from zlib to zlib-ng in the wheels of our latest release. Since then, a macOS 10.14 user has reported a segmentation fault in python-pillow/Pillow#8750, and it appears that zlib-ng is the key difference.

I’ve created a branch at https://github.com/radarhere/Pillow/tree/zlib_demo. radarhere/Pillow@1a38c92 removes almost all Pillow code to set up a simplified reproduction. With that,

1. I build the wheel using GitHub Actions - https://github.com/radarhere/Pillow/actions/runs/13469046394
2. I download the wheel on a macOS 10.14.6 x86_64 machine and install it with python3.11 -m pip install pillow-11.1.0-cp311-cp311-macosx_10_10_x86_64.whl
3. I run the Python code from PIL import _imaging to trigger the C code

The relevant C code in src/_imaging.c is

z_stream z_stream;
z_stream.zalloc = (alloc_func)NULL;
z_stream.zfree = (free_func)NULL;
z_stream.opaque = (voidpf)NULL;

By itself, that does not produce a problem. When I add in radarhere/Pillow@753d484

inflateInit(&z_stream);

at the end then https://github.com/radarhere/Pillow/actions/runs/13469051411 creates another wheel, and there is a segfault - report.txt

If I change the wheel process to target macOS 11 and build on arm64, and then run the resulting wheel on macOS 15, there is no problem.

Thanks for any help.