Re: [Xen-devel] [PATCH for-4.12] dt: fix integer check in dt_device_is_compatible

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 13 Dec 2018, Julien Grall wrote:
> Hi Stefano,
> 
> On 12/12/18 11:53 PM, Stefano Stabellini wrote:
> > On Wed, 12 Dec 2018, Julien Grall wrote:
> > > Hi Stefano,
> > > 
> > > On 11/12/2018 18:46, Stefano Stabellini wrote:
> > > > cplen is unsigned, thus, it can never be < 0. Use a signed integer local
> > > > variable instead.
> > > 
> > > The current code checks > 0. Looking at the code I don't think it can ever
> > > be
> > > negative. So can you details what is the problem you are trying to
> > > resolve?
> > 
> > Yes, it can be "negative" (not actually negative because it is defined
> > as unsigned), in fact it happens with the nodes added dynamically by grub
> > at boot. This patches fixes booting from grub.
> > 
> > Specifically ilen is initialed to 16, but strlen+1 is 17, so length
> > becomes -1. The length of the property generated by grub seems to be
> > short by 1.
> Such explanation should have been in the commit message, it helps to
> diagnostics where the problem is coming from.
> 
> Looking at the specification [1] section 2.3.1, a compatible property is a
> concatenated list of null terminated strings. So the current code is actually
> correct and there is a bug in GRUB.
> 
> This bug was actually fixed by commit ae5817f1d "arm64/xen_boot: Fix Xen boot
> using GRUB2 on AARCH64".
> 
> I assume you are using Grub 2.02 which does not contain the full support for
> Xen. So I would not even consider to work-around it in Xen.
> 
> Instead, I would recommend you to upgrade to a more recent GRUB. It would be
> more likely staging as there are no new GRUB version.
> 
> Another solution is to use chainloading.

it is true that it was a "temporary" bug in grub

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