[dpdk-dev] ABI versioning in Windows

[Thomas Monjalon]

27/05/2020 22:35, Neil Horman:
> On Wed, May 27, 2020 at 02:50:07PM +0200, Thomas Monjalon wrote:
> > +Cc more people
> > 
> > 27/05/2020 12:41, Fady Bader:
> > > What should we do with the ABI versioning in Windows ?
> > 
> > I think there are 2 questions here:
> > 
> > 1/ Do we want to maintain ABI compatibility on Windows like we do for Linux and FreeBSD?
> > The decision must be clearly documented.
> > 
> My first notion, without any greater thought is "why wouldn't we".  ABI
> stability is OS agnostic.  If a symbol is considered stable, theres no reason
> that I can think of that it wouldn't be stable for each OS.

Technical reason + no need so far.


> > 2/ How do we implement the macros in rte_function_versioning.h for Windows?
> > Something needs to be done, otherwise we cannot compile libraries having some function versioning.
> > 
> Can you elaborate on what exactly the issue is here?  I presume by your comment
> above that visual studio either doesn't support symbol level versioning or
> doesn't support versioning at all?

I don't know how to implement the macros in rte_function_versioning.h for Windows.


> If thats the case, and there is a commitment to make dpdk buildable on windows,
> I suppose the only choice is to make a ifdef WINDOWS section of the
> rte_function_versioning.h file, and effectively turn all the macros into no-ops.

Yes that's the idea.
But we still need to implement either BIND_DEFAULT_SYMBOL or MAP_STATIC_SYMBOL
to alias the latest function version to the actual function symbol.

> The BIND_DEFAULT_SYMBOL macro looks like it could still work, as MSVC has an
> alias linker command thats implementable via __pragma, but thats probably all we
> can do, unless there is some more robust versioning support that I can't find.

What is this pragma?


> Note we will also likely need to agument the makefiles/meson files so that the
> link stage doesn't pass the version script to the linker

Why not using the version script for exported symbols?
We are already doing it (.def file generated from .map).