It was never valid taking in a generic shared interface to libc, but a staticall...

sherincall · on May 2, 2021

C language makes a difference between Undefined Behavior and Implementation Defined Behavior. In this case it's the former (n1570 section 7.24.2.1).

Any code that invokes UB is not a valid C program, regardless of implemention.

More practically, ignoring the bug that did happen, libc also has multiple implementations of these functions and picks one based on HW it is running on. So even a statically linked glibc could behave differently on different HW. Always read the docs, this is well defined in the standard.

dooglius · on May 2, 2021

The source code may have had UB, but the compiled program could nevertheless have been bug-free.

> Any code that invokes UB is not a valid C program, regardless of implemention.

I disagree. UB is defined (3.4.3) merely as behavior the standard imposes no requirements upon. The definition does not preclude an implementation from having reasonable behavior for situations the standard considers undefined.

This nuance is very important for the topic at had because many programs are written for specific implementations, not specs, and doing this is completely reasonable.