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Trying to modify RKM V5 boot/root filesystem

PostPosted: Tue Nov 10, 2015 5:53 pm
by joshs
I wanted to make a modification to my RKM V5 boot/root partition, but found something that I don't understand.

The RKM V5 "boot" partition (/dev/mmcblk0p5) includes unexpected compressed data after the initramfs image. That partition begins with a signed gzipped cpio boot filesystem as expected. But then after 0x190 bytes of 0 padding, ending on a 0x200 boundary, I find another equally large chunk of compressed data.

I claim that the data is compressed because when I try compressing it, I only get a 0.125% reduction in size. The 'file' command doesn't recognize the data, and I see no evidence of embedded header information, which leaves me puzzled. I tried treating it as raw gzipped data without a header (c.f. http://unix.stackexchange.com/a/49066), but gunzip complained of a stream error, so I doubt it was gzipped as its cpio counterpart was. In case anyone is wondering, this partition is not a zImage.

Does anyone know what is going on in this partition? Or alternatively, can anyone suggest another way to modify the boot filesystem other than rebuilding the kernel?