CBFS: Automate ROM image layout and remove hardcoded offsets

Non-x86 boards currently need to hardcode the position of their CBFS
master header in a Kconfig. This is very brittle because it is usually
put in between the bootblock and the first CBFS entry, without any
checks to guarantee that it won't overlap either of those. It is not fun
to debug random failures that move and disappear with tiny alignment
changes because someone decided to write "ORBC1112" over some part of
your data section (in a way that is not visible in the symbolized .elf
binaries, only in the final image). This patch seeks to prevent those
issues and reduce the need for manual configuration by making the image
layout a completely automated part of cbfstool.

Since automated placement of the CBFS header means we can no longer
hardcode its position into coreboot, this patch takes the existing x86
solution of placing a pointer to the header at the very end of the
CBFS-managed section of the ROM and generalizes it to all architectures.
This is now even possible with the read-only/read-write split in
ChromeOS, since coreboot knows how large that section is from the
CBFS_SIZE Kconfig (which is by default equal to ROM_SIZE, but can be
changed on systems that place other data next to coreboot/CBFS in ROM).

Also adds a feature to cbfstool that makes the -B (bootblock file name)
argument on image creation optional, since we have recently found valid
use cases for CBFS images that are not the first boot medium of the
device (instead opened by an earlier bootloader that can already
interpret CBFS) and therefore don't really need a bootblock.

BRANCH=None
BUG=None
TEST=Built and booted on Veyron_Pinky, Nyan_Blaze and Falco.

Change-Id: Ib715bb8db258e602991b34f994750a2d3e2d5adf
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: e9879c0fbd57f105254c54bacb3e592acdcad35c
Original-Change-Id: Ifcc755326832755cfbccd6f0a12104cba28a20af
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/229975
Reviewed-on: http://review.coreboot.org/9620
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

3 files changed, 18 insertions, 29 deletions

diff --git a/payloads/libpayload/include/cbfs_core.h b/payloads/libpayload/include/cbfs_core.h
index 42f2dc849f..4599524664 100644
--- a/payloads/libpayload/include/cbfs_core.h
+++ b/payloads/libpayload/include/cbfs_core.h
@@ -85,10 +85,9 @@
 
 #define CBFS_HEADER_INVALID_ADDRESS	((void*)(0xffffffff))
 
-/** this is the master cbfs header - it needs to be located somewhere available
-    to bootblock (to load romstage).  Where it actually lives is up to coreboot.
-    On x86, a pointer to this header will live at 0xFFFFFFFC.
-    For other platforms, you need to define CONFIG_LP_CBFS_HEADER_ROM_OFFSET */
+/* this is the master cbfs header - it must be located somewhere available
+ * to bootblock (to load romstage). The last 4 bytes in the image contain its
+ * relative offset from the end of the image (as a 32-bit signed integer). */
 
 struct cbfs_header {
 	uint32_t magic;
diff --git a/payloads/libpayload/libcbfs/cbfs.c b/payloads/libpayload/libcbfs/cbfs.c
index 5ab7ffa04a..b2b9d61608 100644
--- a/payloads/libpayload/libcbfs/cbfs.c
+++ b/payloads/libpayload/libcbfs/cbfs.c
@@ -62,19 +62,6 @@
 # endif
 #endif
 
-#if defined(CONFIG_LP_CBFS_HEADER_ROM_OFFSET) && (CONFIG_LP_CBFS_HEADER_ROM_OFFSET)
-# define CBFS_HEADER_ROM_ADDRESS (CONFIG_LP_CBFS_HEADER_ROM_OFFSET)
-#else
-/* ugly hack: this assumes that "media" exists
-              in the scope where the macro is used. */
-static uint32_t fetch_x86_header(struct cbfs_media *media)
-{
-	uint32_t *header_ptr = media->map(media, 0xfffffffc, 4);
-	return *header_ptr;
-}
-# define CBFS_HEADER_ROM_ADDRESS fetch_x86_header(media)
-#endif
-
 #include "cbfs_core.c"
 
 #ifndef __SMM__
diff --git a/payloads/libpayload/libcbfs/cbfs_core.c b/payloads/libpayload/libcbfs/cbfs_core.c
index fb15744fe0..eb07e2d292 100644
--- a/payloads/libpayload/libcbfs/cbfs_core.c
+++ b/payloads/libpayload/libcbfs/cbfs_core.c
@@ -34,10 +34,6 @@
  * CBFS_CORE_WITH_LZMA (must be #define)
  *      if defined, ulzma() must exist for decompression of data streams
  *
- * CBFS_HEADER_ROM_ADDRESS
- *	ROM address (offset) of CBFS header. Underlying CBFS media may interpret
- *	it in other way so we call this "address".
- *
  * ERROR(x...)
  *      print an error message x (in printf format)
  *
@@ -56,6 +52,7 @@
  *  on failure */
 const struct cbfs_header *cbfs_get_header(struct cbfs_media *media)
 {
+	int32_t rel_offset;
 	const struct cbfs_header *header;
 	struct cbfs_media default_media;
 
@@ -66,22 +63,28 @@ const struct cbfs_header *cbfs_get_header(struct cbfs_media *media)
 			return CBFS_HEADER_INVALID_ADDRESS;
 		}
 	}
-
 	media->open(media);
-	DEBUG("CBFS_HEADER_ROM_ADDRESS: 0x%x/0x%x\n", CBFS_HEADER_ROM_ADDRESS,
-	      CONFIG_LP_ROM_SIZE);
-	header = media->map(media, CBFS_HEADER_ROM_ADDRESS, sizeof(*header));
+
+	if (!media->read(media, &rel_offset, (size_t)(0 - sizeof(int32_t)),
+			 sizeof(int32_t))) {
+		ERROR("Could not read CBFS master header offset!\n");
+		return CBFS_HEADER_INVALID_ADDRESS;
+	}
+	header = media->map(media, (size_t)rel_offset, sizeof(*header));
+	DEBUG("CBFS header at %#zx (-%#zx from end of image).\n",
+		(size_t)rel_offset, (size_t)-rel_offset);
 	media->close(media);
 
 	if (header == CBFS_MEDIA_INVALID_MAP_ADDRESS) {
-		ERROR("Failed to load CBFS header from 0x%x\n",
-		      CBFS_HEADER_ROM_ADDRESS);
+		ERROR("Failed to load CBFS header from %#zx(-%#zx)\n",
+			(size_t)rel_offset, (size_t)-rel_offset);
 		return CBFS_HEADER_INVALID_ADDRESS;
 	}
 
 	if (CBFS_HEADER_MAGIC != ntohl(header->magic)) {
-		ERROR("Could not find valid CBFS master header at %x: "
-		      "%x vs %x.\n", CBFS_HEADER_ROM_ADDRESS, CBFS_HEADER_MAGIC,
+		ERROR("Could not find valid CBFS master header at %#zx(-%#zx): "
+		      "magic %#.8x vs %#.8x.\n", (size_t)rel_offset,
+		      (size_t)-rel_offset, CBFS_HEADER_MAGIC,
 		      ntohl(header->magic));
 		if (header->magic == 0xffffffff) {
 			ERROR("Maybe ROM is not mapped properly?\n");