bpo-41100: ctypes: check _dyld_shared_cache_contains_path in find_library by lawrence-danna-apple · Pull Request #21241 · python/cpython

the-knights-who-say-ni

System libraries in Mac OS 11 may be present only in the shared cache,
with the actual mach-o file not present in the corresponding location
on the filesystem. ctypes.util.find_library should check the
shared cache in order to behave consistently across Mac OS 10.15
and earlier and Mac OS 11.0 and later.

https://bugs.python.org/issue41100

Is it necessary to add _dyld_shared_cache_contains_path, or is safe to assume libraries in /usr/lib and /lib are in the cache?

In PyObjC similar code to find_library assumes that a library is in the shared cache if (a) the library path starts with "/usr/lib" or "/lib" and (b) there is a symbolic link (such as /usr/lib/libSystem.dylib).

I'm not too happy about using a private symbol, that tends to be fragile.

"I'm not too happy about using a private symbol, that tends to be fragile"

I just spoke to dyld engineers, _dyld_shared_cache_contains_path will be made a public API in Mac OS 11 Seed 3

I was thinking we'd add it as a private symbol now, and then update it to including dyld.h when Seed 3 is out.

"Is it necessary to add _dyld_shared_cache_contains_path, or is safe to assume libraries in /usr/lib and /lib are in the cache?"

I think it is necessary, because if we just assumed any name under /lib was in the cache, then it would think literally anything you ask for is in the cache. find_library("FOO") would return /lib/libFOO.dylib, which is not what we want.

System libraries in Mac OS 11 may be present only in the shared cache,
with the actual mach-o file not present in the corresponding location
on the filesystem.   ctypes.util.find_library should check the
shared cache in order to behave consistently across Mac OS 10.15
and earlier and Mac OS 11.0 and later.