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

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 
developer that the .bss is zero-ed out at startup.
> -- 
> Ross Lagerwall

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