Provide brief documentation about the ChromiumOS kernel layout.
Signed-off-by: Simon Glass <s...@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 */
--
2.41.0.487.g6d72f3e995-goog
