Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals delivered to 64-bit programs

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Fri, Mar 20, 2015 at 02:56:22PM +0300, Cyrill Gorcunov wrote:
> > >
> > > fwiw currently we're passing zero in this __pad0 (replying to your
> > > previous email, so we can workaround in the kernel assuming zero
> > > as a special case, not that good but better than nothing).
> > 
> > Special-casing zero sounds not that bad to me.
> > It can be removed after a few years - just don't forget
> > to document it in a good comment: why we have special
> > case? What software required it?
> > In which version of that software the need to have this hack
> > was eliminated?
> 
> To be fair, such special case would be ideal for us, so that
> if noone object against such hack, i would cook a patch.

Denys, note though that Andy pointed a downside for such approach as well:

 | The only real down side I can see to special casing zero is that it
 | really is possible to end up with zero in there.  For example, the
 | SIGSEGV you get do to the failed sigreturn probably has sigcontext->ss
 | == 0 :)

which I don't know how to resolve.