Re: [ImageBuilder] uboot-script-gen: handle reserved memory regions

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 28 Feb 2025, Luca Miccio wrote:
> Currently, the uboot-script-gen does not account for reserved memory
> regions in the device tree. This oversight can lead to scenarios where
> one or more boot modules overlap with a reserved region. As a result,
> Xen will always crash upon detecting this overlap. However, the crash
> will be silent (without output) if earlyprintk is not enabled, which is
> the default setting at the moment.
> 
> To address this issue, add a function that iterates over the
> reserved-memory nodes and populates an array. This array will be used
> later to calculate the load address for any given file.
> 
> Signed-off-by: Luca Miccio <luca.miccio@xxxxxxx>

Hi Luca,

Thanks for the nice patch! I was waiting for the 4.21 development window
to open.


> ---
>  scripts/uboot-script-gen | 59 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 56 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/uboot-script-gen b/scripts/uboot-script-gen
> index db2c011..cd0d202 100755
> --- a/scripts/uboot-script-gen
> +++ b/scripts/uboot-script-gen
> @@ -468,6 +468,42 @@ function device_tree_editing()
>      fi
>  }
>  
> +function fill_reserved_spaces_from_dtb()
> +{
> +    if [ ! -f $DEVICE_TREE ]
> +    then
> +        echo "File $DEVICE_TREE doesn't exist, exiting";
> +        cleanup_and_return_err
> +    fi
> +
> +    addr_cells=$(fdtget -t x $DEVICE_TREE /reserved-memory '#address-cells')
> +    size_cells=$(fdtget -t x $DEVICE_TREE /reserved-memory '#size-cells')

missing "local" for both variables


> +    for node in $(fdtget -l $DEVICE_TREE /reserved-memory); do
> +        reg_values=($(fdtget -t x $DEVICE_TREE /reserved-memory/$node reg))

missing "local"


> +        for ((i=0; i<${#reg_values[@]}; i+=addr_cells+size_cells)); do
> +            addr=0
> +            size=0

missing "local" for addr and size, and also i and j


> +            for ((j=0; j<addr_cells; j++)); do
> +                addr=$((addr << 32 | 0x${reg_values[i+j]}))
> +            done
> +            
> +            for ((j=0; j<size_cells; j++)); do
> +                size=$((size << 32 | 0x${reg_values[i+addr_cells+j]}))
> +            done
> +            
> +            addr=$(printf "0x%X" $addr)
> +            size=$(printf "0x%X" $size)
> +        done
> +
> +        # Add the reserved space to the list and avoid duplicates
> +        if [[ ! " ${RESERVED_MEM_SPACES[@]} " =~ " ${addr},${size} " ]]; then

I think this is too imprecise as a check because it would match with a
similar element of the array with a higher number of zeros. If I read
this right:

0x1000,0x1000 would match 0x1000,0x10000

I would either remove this check, as it might be OK to have duplicates,
or I would turn it into a proper numeric check, one item at a time in
the list.


> +            RESERVED_MEM_SPACES+=("${addr},${size}")
> +        fi
> +    done
> +}
> +
>  # Read effective image size from a header, which may be larger than the 
> filesize
>  # due to noload sections, e.g. bss.
>  function get_image_size()
> @@ -505,9 +541,24 @@ function add_size()
>          size=${image_size}
>      fi
>  
> -    memaddr=$(( $memaddr + $size + $offset - 1))
> -    memaddr=$(( $memaddr & ~($offset - 1) ))
> -    memaddr=`printf "0x%X\n" $memaddr`
> +    # Try to place the file at the first available space...
> +    local new_memaddr=$(( (memaddr + size + offset - 1) & ~(offset - 1) ))
> +
> +    # ...then check if it overlaps with any reserved space
> +    for reserved_space in "${RESERVED_MEM_SPACES[@]}"; do
> +        local reserved_start=${reserved_space%,*}
> +        local reserved_size=${reserved_space#*,}
> +        local reserved_end=$((reserved_start + reserved_size))
> +
> +        if [[ $new_memaddr -le $reserved_end ]] && \
> +           [[ $((new_memaddr + size)) -ge $reserved_start ]]; then
> +            # In that case, place the file at the next available space
> +            # after the reserved one
> +            new_memaddr=$(( (reserved_end + offset) & ~(offset - 1) ))
> +        fi
> +    done
> +
> +    memaddr=$(printf "0x%X\n" $new_memaddr)
>      filesize=$size
>  }
>  
> @@ -1373,6 +1424,8 @@ uboot_addr=$memaddr
>  memaddr=$(( $memaddr + $offset ))
>  memaddr=`printf "0x%X\n" $memaddr`
>  
> +fill_reserved_spaces_from_dtb
> +
>  if test "$os" = "xen"
>  then
>      xen_file_loading
> -- 
> 2.25.1
>