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



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



 


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