Re: ABI guarantees

On Fri, Aug 15, 2025 at 8:26 AM Konstantin Belousov <kostikbel@gmail.com> wrote:
>
> I think that now is the time to discuss the project ABI stability guarantees
> that we provide for the system as the whole.  My personal opinion always is
> that FreeBSD should aim at providing the perfect compatibility.  This can
> be formulated at two levels:
> - from high level view, an app depending on the base library or kernel
>   feature, should never break.
> - a view from the low side would list the technical aspects of things,
>   that allows to provide the guarantee of the high level view.
>
> We have a lot of facilities to allow the base system evolution while still
> having the stability of interfaces.  I might try to enumerate all that
> features, below is incomplete but representative list of examples:
> - versioning of dsos, both as dso version, and fine-grained symbol versions
> - definition of boundaries, where we provide the binary consumers a view
>   on implementation  (e.g. syscall interfaces, kernel compat syscalls).
> - rtld tricks to provide expected execution environments from older
>   releases on modern systems.
> - kernel support for old binaries formats, older p_osrel, ELF notes to
>   record compilation environment of the binary, etc.
> But the complete list of low level features to handle ABI stability while
> evolving, is not the point.  The users really only care about the high
> level view, they need ability to run the old binaries on their modern
> systems.
>
> So, do we as the project strive to fullfill this goal?  Note that ABI compat
> is not a grading scale: if system fail running some binary, then the compat
> failed.  This is why the feature is hard, in addition to the lot of subtle
> technical details to care about, there needs to be a constistent efforts
> to properly maintain it.
>
> I am asking about the project goal because the common theme of several
> recent commits or, put it differently, breakage from them, were ABI
> breakage.  If we care, then we need to care more.  If not, then the
> policy should be clearly formulated and the burden ease on the developers.
>
> I do hope that we would continue care about ABI. Of course with our resources
> we cannot be perfect at level of Windows, but we can do much better than
> we do now.
>
> The stability (as in ABI stability) was one of the features of FreeBSD
> that was the reason to use and care about it as the main personal
> computing platform. I expect that a lot of users also depend on this
> aspect, judging by the reaction to the broken stuff (and some non-public
> feedback on things like iBCS2 compat removal etc).

+1 :-)

-- 
CeDeROM, SQ7MHZ, http://www.tomek.cedro.info