[CRIU] [PATCH] rst alloc: align on reporting cpos too

[Tycho Andersen]

On Wed, Feb 10, 2016 at 04:37:59PM +0300, Pavel Emelyanov wrote:
> On 02/09/2016 08:38 PM, Tycho Andersen wrote:
> > Since we align in rst_mem_alloc, we should also align when reporting the
> > current position; if we don't and things get unlucky, we report a different
> > position than where the pointer is actually allocated, which fucks things
> > up quite bad :)
> 
> Applied, thanks.
> 
> However, if I do this:
> 
> x = rst_mem_cpos()
> x2 = rst_mem_alloc_cont()
> 
> then x will not correspond to x2 since the latter doesn't align what
> it allocates.

Oh, yep :(.

> I've proposed to introduce a call rst_mem_alogn() that would just
> shift the "free" pointer up to the nearest aligned value. With this
> any combination would work.

Not sure I understand the call pattern you're proposing here. Can you
elaborate? IIUC, the only way to fix this is to add a
rst_mem_cpos_cont() call that is used with rst_mem_alloc_cont(), and
then go fix each call site. Maybe that's what you were suggesting and
I misunderstood :)

Tycho

> -- Pavel
> 
> > Closes #111
> > 
> > Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
> > ---
> >  rst-malloc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/rst-malloc.c b/rst-malloc.c
> > index 3556980..8e17255 100644
> > --- a/rst-malloc.c
> > +++ b/rst-malloc.c
> > @@ -128,7 +128,7 @@ unsigned long rst_mem_cpos(int type)
> >  {
> >  	struct rst_mem_type_s *t = &rst_mems[type];
> >  	BUG_ON(!t->remapable || !t->enabled);
> > -	return t->free_mem - t->buf;
> > +	return ((void*) round_up((unsigned long)t->free_mem, sizeof(void *))) - t->buf;
> >  }
> >  
> >  void *rst_mem_remap_ptr(unsigned long pos, int type)
> > 
>