[CRIU] [PATCH 7/8] restore: Add restoration of alternative signal stack

[Cyrill Gorcunov]

On Tue, Jun 18, 2013 at 05:43:21PM +0400, Andrew Vagin wrote:
> > task, iow simultaneously with setting up new cs:ip. So I don't get how
> > it's related to nested signal handlers.
> 
> It was off topic question.

ok

> > own signal handler, no?
> yes. But when I wrote this message I did not know that altstack is used
> only for SA_ONSTACK, so we can restore sas here.

ok, thanks!

> > In turn former blocked signals mask is restored
> > sigreturn too, thus (if only I've not missed something obvious) -- we're
> > allowed to restore sas with sigreturn help insted of explicit calling
> > for sigaltstack() system routine.
> 
> So why do we call sigaltstack?

We call sigaltstack in only one case -- on dump, to fetch the value(s)
dumpee has. On restore we have 2 ways

 - either call for sigaltstack explicitly in restorer.c right before
   we call for sigreturn

 - either pass stack value to sigreturn call and allow the kernel to
   restore stack for us

I chose second way and simply tune up sigframe. Sounds reasonable?