The kernel internally makes no promises about ABI even in C, why would that change for Rust?
For userspace, Rust doesn't export anything new to userspace. The kernel APIs remain as they were, and Linus has the same view as ever about whether it's OK to break userspace.
I mean how do they plan to interop between C and Rust code. Either in the same library or across shared libraries (if written in Rust, what does it export on the API surface such that C code can call into it)?
> The kernel internally makes no promises about ABI even in C
There might be two different definitions of “ABI” in this thread.
The kernel indeed makes no promises regarding e.g. the order in which structure members are declared or the stability of that order from version to version.
It probably can be said, though, to promise (through its interaction with the C compiler) that if you take a structure declaration as it appears in the source code, then in a normally-compiled kernel that structure will be laid out in a manner that’s predictable and most probably even described in a human-readable document. Those rules usually have not changed for decades (even if I sometimes wish they were different).
As far as I know, unless you ask for that specifically, the Rust compiler does not promise any of that, the only documentation for what it will do by default is the source code, and it is free to change the rules from version to version with no notice.
