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

Cyrill Gorcunov
2015-03-20T12:04:25Z

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.