Re: [PATCH qemu] ppc/vof: Fix Coverity issues

[David Gibson]

On Mon, Jul 19, 2021 at 06:25:53PM +1000, Alexey Kardashevskiy wrote:
> 
> 
> On 7/19/21 13:57, David Gibson wrote:
> > On Tue, Jul 13, 2021 at 11:46:38PM +1000, Alexey Kardashevskiy wrote:
> > > This fixes NEGATIVE_RETURNS, OVERRUN issues reported by the Coverity.
> > > 
> > > This adds a comment about the return parameters number in the VOF hcall.
> > > The reason for such counting is to keep the numbers look the same in
> > > vof_client_handle() and the Linux (an OF client).
> > > 
> > > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > > ---
> > > 
> > > Will this make COverity happy? What is the canonical way of fixing these
> > > uint32_t vs. int? Thanks,
> > 
> > It might make Coverity happy, but I think it's an ugly approach.
> > 
> > > 
> > > ---
> > >   hw/ppc/vof.c | 12 ++++++++----
> > >   1 file changed, 8 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c
> > > index 81f65962156c..872f671babbe 100644
> > > --- a/hw/ppc/vof.c
> > > +++ b/hw/ppc/vof.c
> > > @@ -517,7 +517,7 @@ static uint32_t vof_instance_to_package(Vof *vof, 
> > > uint32_t ihandle)
> > >   static uint32_t vof_package_to_path(const void *fdt, uint32_t phandle,
> > >                                       uint32_t buf, uint32_t len)
> > >   {
> > > -    uint32_t ret = -1;
> > > +    int ret = -1;
> > 
> > I don't think you want to try to use the same variable for the value
> > from phandle_to_path() and the return value from this function -
> > they're different types, with different encodings.  The inner value
> > should remain int (that's the libfdt convention).
> > 
> > The outer one is explicltly unsigned.  You're not really looking for
> > negative error values, but specifically for -1U == ~0U as the single
> > error value.  So re-introduce your PROM_ERROR valued, defined as ~0U,
> > so that it's clearly unsigned, and use that and unsigned logic for all
> > manipulation of the outer value.
> 
> 
> Fair enough. One question. Linux defines it as
> 
> #define PROM_ERROR (-1u)
> 
> Do you still vote for "~0U"?

I don't really mind.  I think (-1U) might cause some more Coverity
confusion that ~0U, based on experience with Coverity scans of dtc &
libfdt.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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