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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 6 Mar 2025, Stefano Stabellini wrote:
> 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')

One more comment. If the DT doesn't have any reserved memory regions:

Error at '/reserved-memory': FDT_ERR_NOTFOUND
Error at '/reserved-memory': FDT_ERR_NOTFOUND
Error at '/reserved-memory': FDT_ERR_NOTFOUND

It would be best to silence these errors


> 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
> > 
>