Re: [PATCH] [RFC] Emulate "lwsync" to run standard user land on e500 cores

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2013-10-25 at 10:58 +0100, David Laight wrote:
> > This is not a distro issue. It's a libstdc++ portability issue. libstdc++
> > hardcodes lwsync unless __NO_LWSYNC__ is explicitly defined,
> > which you only get with -mcpu=8540/-mcpu=8548.  When compiled
> > for any powerpc target other than -mcpu=8540/-mcpu=8548, including
> > the default -mcpu=common,  libstdc++ will end up containing lwsync.
> > There is no way to explicitly request libstdc++ to be built without lwsync
> > with an -mcpu target other than 8540/8548.
> > 
> > The issue is easily demonstrated by running a program that throws a
> > C++ exception: __cxa_throw() is called, which has an lwsync.  This
> > results in an illegal instruction exception when run on an e500v1/e500v2.
> 
> Perhaps libstc++ should be working out at run time whether lwsync is valid?

Do we have enough coats of paint on this bike shed yet ? :-)

I'm personally tempted to take Scott's approach since that's what we do
for other things as well, it just works and is simple.

Cheers,
Ben.