[U-Boot] Size of FDT image

[Yousf Ateya]

Dears,

I am calculating images check-sum in common/bootm.c (in function
do_bootm_states
<https://git.denx.de/?p=u-boot.git;a=blob;f=common/bootm.c;h=9493a306cd038d86b08575dba7cf97a1238933f6;hb=c253573f3e269fd9a24ee6684d87dd91106018a5#l603>)
for security reasons. I am using contents of images structure to do so.
Code is similar to this:

int os_cs = checksum(images.os.image_start, images.os.image_len); //Always
> consistent
> int initrd_cs = checksum(images.initrd_start, images.initrd_end -
> images.initrd_start); //Always consistent
> int ft_cs = checksum(images.ft_addr, images.ft_len); //Changes after power
> reset
>
> printf("Checksums: OS %d, initrd %d, FTD %d\n", os_cs, initrd_cs, ft_cs);
>


Both OS, and initrd images are working perfectly. FDT image checksum is the
same through software reboots, but it changes after power reset (fully
remove power, and connect power again); Which makes me suspect garbage data
at end of images.ft_addr.

I tried to do partial checksum for FTD image (only 80% of its size)

int ft_cs = checksum(images.ft_addr, images.ft_len * 0.8); //Always
> consistent
>

Then checksum worked perfectly through power resets. But it is not good
idea to check-sum part of image only.

I think there is unused area at the end of image length that changes in
power resets.

Is there a way to get actual FDT image length?

Using version v2017.11
<https://git.denx.de/?p=u-boot.git;a=shortlog;h=refs/tags/v2017.11>

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