[simonask]

> In the C ecosystem, the compiler gets to define what UB means.

It really doesn't though. The current revision of the ISO/IEC 9899 standards document gets to define it, nobody else.

[hedora]

No; that says what things have undefined behavior in the language spec.

The compiler / os / hw platform are free to define the behavior of those things. Leaving them undefined at the language spec is the mechanism that allows them to be defined by the underlying system. C has worked this way since its initial release.