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

[Andrew Cooper <andrew.cooper3@citrix.com>]

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.  Also,
it doesn't help the compilation error if someone ends up disabling
assert() by playing with NDEBUG.

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

---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.  Initialise the parameters to safe defaults.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>