Re: cxx-mem-model merge [6 of 9] - libstdc++-v3

[Hans-Peter Nilsson <hans-peter.nilsson@axis.com>]

> From: "Joseph S. Myers" <joseph@codesourcery.com>
> Date: Mon, 7 Nov 2011 17:24:04 +0100

> On Mon, 7 Nov 2011, Andrew MacLeod wrote:
> 
> > Actually, this target has no lock free support whatsoever?  ie, no
> > compare_and_swap instruction, nor an implementation of sync_lock_test_and_set
> > and sync_lock_release?
> > 
> > I think the libstdc++ standard now requires the class atomic_flag to be lock
> > free in order to conform (n3242 29.7.2)
> > 
> > So I guess this is the situation which all the atomic tests are not even
> > suppose to be run since they aren't supported.  My guess is that in the
> > previous releases the c++ header files probably provided a locked
> > implementation of test_and_set, and so the tests would run.
> 
> For bare-metal targets there should maybe be an option to presume there is 
> just one thread and map all atomic operations to dumb non-atomic versions, 
> which is perfectly valid in such a case.  But that's a new feature; we 
> didn't have it for __sync_* either.

It'd not be a new feature, that's apparently how it worked until
it broke now ...unless you mean something different.

brgds, H-P