Re: [XEN v5 02/10] xen/arm: Typecast the DT values into paddr_t

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 19/04/2023 15:58, Ayan Kumar Halder wrote:
> On 19/04/2023 14:54, Michal Orzel wrote:
> > On 19/04/2023 15:19, Michal Orzel wrote:
> > > Hi Ayan,
> > >
> > > On 13/04/2023 19:37, Ayan Kumar Halder wrote:
> > > > The DT functions (dt_read_number(), device_tree_get_reg(), 
> > > > fdt_get_mem_rsv())
> > > > currently accept or return 64-bit values.
> > > >
> > > > In future when we support 32-bit physical address, these DT 
> > > > functions are
> > > > expected to accept/return 32-bit or 64-bit values (depending on the 
> > > > width of
> > > > physical address). Also, we wish to detect if any truncation has 
> > > > occurred
> > > > (i.e. while parsing 32-bit physical addresses from 64-bit values 
> > > > read from DT).
> > > > device_tree_get_reg() should now be able to return paddr_t. This is 
> > > > invoked by
> > > > various callers to get DT address and size.
> > > >
> > > > For fdt_get_mem_rsv(), we have introduced a wrapper named
> > > > fdt_get_mem_rsv_paddr() which will invoke fdt_get_mem_rsv() and 
> > > > translate
> > > > uint64_t to paddr_t. The reason being we cannot modify 
> > > > fdt_get_mem_rsv() as it
> > > > has been imported from external source.
> > > >
> > > > For dt_read_number(), we have also introduced a wrapper named 
> > > > dt_read_paddr()
> > > > dt_read_paddr() to read physical addresses. We chose not to modify 
> > > > the original
> > > > function as it is used in places where it needs to specifically read 
> > > > 64-bit
> > > > values from dt (For e.g. dt_property_read_u64()).
> > > >
> > > > Xen prints warning when it detects truncation in cases where it is 
> > > > not able to
> > > > return error.
> > > >
> > > > Also, replaced u32/u64 with uint32_t/uint64_t in the functions touched
> > > > by the code changes.
> > > >
> > > > Also, initialized variables to fix the warning 
> > > > "-Werror=maybe-uninitialized".
> > > I can see that now you explicitly set to 0 variables passed to 
> > > fdt_get_mem_rsv_paddr()
> > > which haven't been initialized before being passed to 
> > > fdt_get_mem_rsv(). Is this what
> > > you are reffering to? I cannot reproduce it, hence my question.
> > I can see why did you get this error.
> > Before your change, we always checked for an error from 
> > fdt_get_mem_rsv() by checking if < 0.
> > In your wrapper fdt_get_mem_rsv_paddr(), you switched (not sure why) 
> > to checking if not zero.
> > Becasue of this, you got an error and tried to fix it by initializing 
> > the variables to 0.
> I actually wanted to return the error code obtained from 
> fdt_get_mem_rsv() to the caller.
> In this case, it returns a single error code.
I would rather not rely on this.

> So does this look sane to 
> you ?
> diff --git a/xen/include/xen/libfdt/libfdt-xen.h 
> b/xen/include/xen/libfdt/libfdt-xen.h
> index 3296a368a6..1da87d6668 100644
> --- a/xen/include/xen/libfdt/libfdt-xen.h
> +++ b/xen/include/xen/libfdt/libfdt-xen.h
> @@ -22,9 +22,8 @@ static inline int fdt_get_mem_rsv_paddr(const void 
> *fdt, int n,
>       uint64_t dt_size;
>       int ret = 0;
>
> -    ret = fdt_get_mem_rsv(fdt, n, &dt_addr, &dt_size);
> -    if ( ret )
> -        return ret;
> +    if ( fdt_get_mem_rsv(fdt, n, &dt_addr, &dt_size) < 0 )
> +        return -FDT_ERR_BADOFFSET;
So the problem if you check for ret to be non-zero. But the caller of 
fdt_get_mem_rsv_paddr() check for < 0.
Given that fdt_get_mem_rsv() is not inline, the compiler doesn't know 
that it will not return a positive value (other than 0). Hence why I 
think you get an unitialize value.
The snippet below should work:

if ( ret < 0 )
  return ret;

Cheers,

--
Julien Grall