Include 0xea byte as the last byte in RO/RW images

This is better than having the 0xea byte only appended in ec.bin,
since now the byte is present in ec.RW.flat and ec.RO.flat.  Needed
for EC software sync.

BUG=chrome-os-partner:12412
BRANCH=link,snow
CQ-DEPEND=30305
TEST=manual

1. xxd ec.RW.bin | tail; should end with 0xea
2. xxd -g4 build/link/ec.bin | grep -C3 454e44ea

That word should be the last one before a bunch of 0xfffffff bytes.
There should be 2 matches (since there's RO and RW firmware)

Change-Id: I0de5cc78083f1a9b49202fbe2305a3101f401db3
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/30303
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

2 files changed, 17 insertions, 6 deletions

diff --git a/common/system_common.c b/common/system_common.c
index 00b754c037..e2dcddc342 100644
--- a/common/system_common.c
+++ b/common/system_common.c
@@ -245,15 +245,15 @@ int system_get_image_used(enum system_image_copy_t copy)
 	if (size <= 0)
 		return 0;
 
-	/* If the last byte isn't 0xff, the image is completely full */
-	if (image[size - 1] != 0xff)
-		return size;
-
-	/* Scan backwards looking for 0xea byte */
+	/*
+	 * Scan backwards looking for 0xea byte, which is by definition the
+	 * last byte of the image.  See ec.lds.S for how this is inserted at
+	 * the end of the image.
+	 */
 	for (size--; size > 0 && image[size] != 0xea; size--)
 		;
 
-	return size;
+	return size ? size + 1 : 0;  /* 0xea byte IS part of the image */
 }
 
 /* Returns true if the given range is overlapped with the active image.
diff --git a/core/cortex-m/ec.lds.S b/core/cortex-m/ec.lds.S
index 53c5960045..393c6c4bc6 100644
--- a/core/cortex-m/ec.lds.S
+++ b/core/cortex-m/ec.lds.S
@@ -136,7 +136,18 @@ SECTIONS
 	/* Shared memory buffer must be at the end of preallocated RAM, so it
 	 * can expand to use all the remaining RAM. */
 	__shared_mem_buf = .;
+
+	/* Tag at end of firmware image so that we can find the image size.
+	 * This may be overwritten by the shared memory buffer; that's ok
+	 * because we only use it to find the image size in flash. */
+        . = ALIGN(4);
+        BYTE(0x45);
+        BYTE(0x4e);
+        BYTE(0x44);
+        BYTE(0xea);
+	/* NOTHING MAY GO AFTER THIS! */
     } > IRAM
+
     /* The linker won't notice if the .data section is too big to fit,
      * apparently because we're sending it into IRAM, not FLASH. The following
      * symbol isn't used by the code, but running "objdump -t *.elf | grep hey"