log: Preserve Kukui EC reset logs across every EC reboot on SRAM.

On Kukui, we need to put console logs and reset reasons at fixed
addresses on SRAM to save the information across each EC resets.
Otherwise, EC will lose console logs and reset reasons after resetting
EC.

This CL ensures that the contents of reset and console logs will not be
clobbered or cleared by putting mandatory symbols at a fixed location on
SRAM. The values will only be reset when checksum or sanity check fails.

BUG=b:133795403
TEST=1. On Kukui, shutdown AP, reboot AP, or sysjump, and see
	the previous logs before reboot will be kept
        on /var/log/croc_ec.log
     2. Reset reasons can be viewed with ectool uptimeinfo
BRANCH=master

Change-Id: I19db49101fda1675dc2fdc047b7f14af77cdb6e6
Signed-off-by: Shannon Chen <shannc@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1716671
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Yilun Lin <yllin@chromium.org>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
Commit-Queue: Shannon Chen <shannc@chromium.org>
Tested-by: Shannon Chen <shannc@chromium.org>

1 files changed, 24 insertions, 4 deletions

diff --git a/core/cortex-m0/ec.lds.S b/core/cortex-m0/ec.lds.S
index 42e0b2e034..953433459a 100644
--- a/core/cortex-m0/ec.lds.S
+++ b/core/cortex-m0/ec.lds.S
@@ -191,16 +191,36 @@ SECTIONS
         . = ALIGN(4);
     } > FLASH
     __data_lma_start = . ;
-
-    .bss : {
+    .vtable : {
 	/*
-	 * Vector table must be at the beginning of bss section. The vector
+	 * Vector table must be at the base of SRAM. The vector
 	 * table section contains a RAM copy of the vector table used on
 	 * STM chips for relocating the vector table.
 	 */
 	. = ALIGN(8);
-	__bss_start = .;
 	*(.bss.vector_table)
+	. = ALIGN(8);
+    } > IRAM
+
+#ifdef CONFIG_PRESERVE_LOGS
+    .preserve_logs(NOLOAD) : {
+	/*
+	 * The size of the vector table is fixed. Thus, the address of
+	 * the preserved logs is also fixed.
+	 */
+	. = ALIGN(8);
+	*(SORT(.preserved_logs.*))
+	. = ALIGN(8);
+	__preserved_logs_end = .;
+    } > IRAM
+
+    ASSERT((SIZEOF(.vtable) + SIZEOF(.preserve_logs) + CONFIG_RAM_BASE) ==
+	__preserved_logs_end, "preserve_logs must be right after vtable")
+#endif
+
+    .bss : {
+	. = ALIGN(8);
+	__bss_start = .;
 	/* Stacks must be 64-bit aligned */
         . = ALIGN(8);
         *(.bss.system_stack)