Re: [dpdk-dev] ABI versioning in Windows

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, May 27, 2020 at 11:43:49PM +0200, Thomas Monjalon wrote:
> 27/05/2020 23:27, 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.
> 
> I've just found a tip in https://sourceware.org/binutils/docs/ld/WIN32.html
> It suggests to create a weak symbol:
> void foo() __attribute__((weak, alias ("foo_latestversion")));
> 
Ahh, you're using mingw, which appears to support versioning.  If the windows
equivalent of ld.so honors those versions, I would think the versioning bits
should almost just work (assuming that mingw supports all the used
__attirbutes__)

Neil

> 
> > > 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).
> 
> 
> 
>