CPython records and propagates several compilation-related flags from the time CPython is built, which in turn are used by distutils and setuptools to pass them to extension modules.

Unfortunately after pypa/distutils#228, distutils now introduced a new LDCXXSHARED, and are using that in preference to LDSHARED when linking C++ code. We do set LDCXXSHARED but we don't propagate LDFLAGS to that variable if the user has set in the environment.

This is a problem because many distributions use the old variable LDFLAGS to propagate linker flags to extension modules (such as hardening and configuration flags) and now these are silently failing for C++ extension modules.

Linked PRs

• gh-123297: Propagate LD_FLAGS to LDCXXSHARED in sysconfig #123298
• [3.13] gh-123297: Propagate LD_FLAGS to LDCXXSHARED in sysconfig (GH-123298) #123319
• [3.12] gh-123297: Propagate LD_FLAGS to LDCXXSHARED in sysconfig (GH-123298) #123320