Revert "boot - don't interpet end of image as trailer."
This reverts commit 920fc16b8968c580c1d0ab438d08296bdb2d3b9c.
The boot loader records its current state in the form of a pair of image
trailers, each located at the end of the corresponding image slot. If
an image is so big that it extends into the trailer space of a slot, the
boot loader would read the end of the image and interpet it as the start
of a trailer. The fix was to determine the size of each image upfront
by reading their headers, and only attempt to read an image's trailer if
the image is small enough that it doesn't extend into the trailer space.
If an image is too big to allow for a trailer, the boot loader fails
over to its "rescue mode": just boot into whatever is in slot 0.
The problem arises when the boot loader reads the image headers. There
are certain points during a swap when an image header is not in the
expected location. That is, if the device reboots at the wrong time
during an image swap, the boot loader will fail to read the image
headers when it comes up.
The image sectors are swapped in reverse order. When a swap is
performed, the final sectors of each slot are swapped first, and the
first sectors (containing the image headers) get swapped last. During
the final swap operation, there are two points at which the image
headers are not in the expected place:
1. slot 1 erased; header 1 in scratch area.
2. slot 0 erased; header 0 in scratch area.
In each case, the image header is not actually missing. Rather, the
boot loader is just looking in the wrong place. It should be looking in
the scratch area, not the start of the image slot.
The fix is to revert the original commit. Now, the boot loader won't
fail when an image header read fails. It is the user's responsibility
to ensure an image isn't too big.
5 files changed