[3.12] gh-126554: ctypes: Correctly handle NULL dlsym values (GH-126555)

[picnixz]

For dlsym(), a return value of NULL does not necessarily indicate
an error 1.

Therefore, to avoid using stale (or NULL) dlerror() values, we must:

1. clear the previous error state by calling dlerror()
2. call dlsym()
3. call dlerror()

If the return value of dlerror() is not NULL, an error occured.

In ctypes we choose to treat a NULL return value from dlsym()
as a "not found" error. This is the same as the fallback
message we use on Windows, Cygwin or when getting/formatting
the error reason fails.

(cherry picked from commit 8717f79)

Co-authored-by: George Alexopoulos [email protected]
Signed-off-by: Georgios Alexopoulos [email protected]
Signed-off-by: Georgios Alexopoulos [email protected]
Co-authored-by: Peter Bierma [email protected]
Co-authored-by: Bénédikt Tran [email protected]
Co-authored-by: Petr Viktorin [email protected]

• Issue: ctypes: We do not correctly handle NULL dlsym() return values #126554

[picnixz]

I've opened the backport PR so that we are consistent with backporting. But the diff is quite non-trivial since the backport was not automatic. So if you don't want to lose time, we can just say "let's not backport 3.12" (even though you said that you didn't care).

I'm marking the PR as a draft so that we don't merge by mistake.

EDIT 1: Ok I think I messed up the backport.
EDIT 2: I won't be able to check this for the rest of the week.

[serhiy-storchaka]

Thanks, @picnixz.