Re: [Xen-devel] [PATCH] tools/libxc: Initialise parameters in map_p2m_list() for error paths

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2016-01-07 at 15:24 +0000, Andrew Cooper wrote:
> On 07/01/16 15:06, Ian Campbell wrote:
> > On Thu, 2016-01-07 at 14:55 +0000, Andrew Cooper wrote:
> > > c/s 7bf7458 "libxc: support of linear p2m list for migration of
> > > pv-domains" breaks compilation on CentOS 7 because of 'ptes' being
> > > possibly uninitialised after the 'err:' label.
> > > 
> > > The migration will fail early for conditions which would cause the
> > > for()
> > > loop not to run, but the compiler doesn't know this.
> > Isn't the issue the malloc goto err path before the loop? Looks like
> > that
> > should have the error behaviour from the earlier half of the function
> > rather than the latter.
> 
> So it is - I missed that one when looking the options.
> 
> > 
> > There might also be a path if ctx->x86_pv.levels == 0, in which case
> > the
> > loop will never run, that's the sort of thing which could be checked
> > (or
> > even perhaps asserted) on entry to the function.
> 
> I don't think asserting details like this is a scalable options.ÂÂAlso,
> it doesn't help the compilation error if someone ends up disabling
> assert() by playing with NDEBUG.

It could be an error return instead (which is what I meant to suggest
without the parenthetical).

> All that is needed is an adjustment to the commit message IMO:

I can live with this.

> 
> ---8<---
> tools/libxc: Initialise parameters in map_p2m_list() for error paths
> 
> c/s 7bf7458 "libxc: support of linear p2m list for migration of
> pv-domains" breaks compilation on CentOS 7 because of 'ptes' being
> possibly uninitialised after the 'err:' label.
> 
> Indeed, the malloc() failure path would end using 'ptes' while
> uninitialised.ÂÂInitialise the parameters to safe defaults.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 

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