Re: [Xen-devel] [PATCH v4 1/9] livepatch: Clear .bss when payload is reverted

[Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>]

On 09/09/2016 02:50 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 09, 2016 at 02:33:18PM +0100, Ross Lagerwall wrote:
> > On 08/24/2016 03:22 AM, Konrad Rzeszutek Wilk wrote:
> > > So that when we apply the patch again the .bss is cleared.
> > > Otherwise we may find some variables containing old values.
> > >
> > > The payloads may contain various .bss - especially if -fdata-sections
> > > is used which can create .bss.<name> sections.
> > After having thought about this again, I'm not sure it makes much sense. Any
> > data sections in the payload are not reset to their initial values, so
> > resetting the bss only may result in an unexpected combination of new & old
> > data/bss.
> Regardless of that I think clearing the .bss upon applying the livepatch is
> still the right thing to do.
>
> Regarding of the .data - we could have a copy of the .data the first time
> we load - and then during application copy over it from the original one?.
>
> > Perhaps it just needs to be documented that a payload's bss/data is
> > untouched across revert/apply?
> It really cuts down on bugs if we clear the .bss. It is kind of ingrained in 
> every
> developer that the .bss is zero-ed out at startup.
> >
Sure.

IMO clearing one but not resetting the other is even more unexpected. 
However, if we agree that it is desirable to do both, then this patch is 
acceptable as a step in the right direction.
--
Ross Lagerwall

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