Provide brief documentation about the ChromiumOS kernel layout.
Signed-off-by: Simon Glass sjg@chromium.org ---
boot/bootmeth_cros.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+)
diff --git a/boot/bootmeth_cros.c b/boot/bootmeth_cros.c index 3b9e75540aa8..a551d43701d8 100644 --- a/boot/bootmeth_cros.c +++ b/boot/bootmeth_cros.c @@ -22,6 +22,35 @@ #include <linux/sizes.h> #include "bootmeth_cros.h"
+/* + * Layout of the ChromeOS kernel + * + * Partitions 2 and 4 contain kernels + * + * Contents are: + * + * Offset Contents + * 0 struct vb2_keyblock + * m struct vb2_kernel_preamble + * m + n kernel buffer + * + * m is keyblock->keyblock_size + * n is preamble->preamble_size + * + * The kernel buffer itself consists of various parts: + * + * Offset Contents + * m + n kernel image (Flat vmlinux binary or FIT) + * b - 8KB Command line text + * b - 4KB X86 setup block (struct boot_params, extends for about 16KB) + * b X86 bootloader (continuation of setup block) + * b + 16KB X86 setup block (copy, used for hold data pointed to) + * + * b is m + n + preamble->bootloader_address - preamble->body_load_address + * + * Useful metadata extends from b - 8KB through to b + 32 KB + */ + enum { PROBE_SIZE = SZ_4K, /* initial bytes read from partition */