[U-Boot] [PATCH v0 21/20] efi_loader: hack for archs that cannot do unaligned accesses

[Rob Clark]

Some arch's have trouble with unaligned accesses.  Technically
EFI device-path structs should be byte aligned, and the next node
in the path starts immediately after the previous.  Meaning that
a pointer to an 'struct efi_device_path' is not necessarily word
aligned.  See section 10.3.1 in v2.7 of UEFI spec.

This causes problems not just for u-boot, but also most/all EFI
payloads loaded by u-boot on these archs.  Fortunately the common
practice for traversing a device path is to rely on the length
field in the header, rather than the specified length of the
particular device path type+subtype.  So the EFI_DP_PAD() macro
will add the specified number of bytes to the tail of device path
structs to pad them to word alignment.

Technically this is non-compliant, BROKEN_UNALIGNED should *only*
be defined on archs that cannot do unaligned accesses.

Signed-off-by: Rob Clark <robdclark at gmail.com>
---
I'm not sure if there are other arch's that need -DBROKEN_UNALIGNED

Mark, this is untested but I think it should solve your crash on the
Banana Pi.  Could you give it a try when you get a chance?

 arch/arm/config.mk               |  2 +-
 include/efi_api.h                | 30 ++++++++++++++++++++++++++++++
 lib/efi_loader/efi_device_path.c |  3 +++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index 1a77779db4..067dc93a9d 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -28,7 +28,7 @@ LLVMS_RELFLAGS		:= $(call cc-option,-mllvm,) \
 			$(call cc-option,-arm-use-movt=0,)
 PLATFORM_RELFLAGS	+= $(LLVM_RELFLAGS)
 
-PLATFORM_CPPFLAGS += -D__ARM__
+PLATFORM_CPPFLAGS += -D__ARM__ -DBROKEN_UNALIGNED
 
 ifdef CONFIG_ARM64
 PLATFORM_ELFFLAGS += -B aarch64 -O elf64-littleaarch64
diff --git a/include/efi_api.h b/include/efi_api.h
index ef91e34c7b..ddd1e6100a 100644
--- a/include/efi_api.h
+++ b/include/efi_api.h
@@ -284,6 +284,31 @@ struct efi_loaded_image {
 #define DEVICE_PATH_TYPE_END			0x7f
 #  define DEVICE_PATH_SUB_TYPE_END		0xff
 
+/*
+ * Some arch's have trouble with unaligned accesses.  Technically
+ * EFI device-path structs should be byte aligned, and the next node
+ * in the path starts immediately after the previous.  Meaning that
+ * a pointer to an 'struct efi_device_path' is not necessarily word
+ * aligned.  See section 10.3.1 in v2.7 of UEFI spec.
+ *
+ * This causes problems not just for u-boot, but also most/all EFI
+ * payloads loaded by u-boot on these archs.  Fortunately the common
+ * practice for traversing a device path is to rely on the length
+ * field in the header, rather than the specified length of the
+ * particular device path type+subtype.  So the EFI_DP_PAD() macro
+ * will add the specified number of bytes to the tail of device path
+ * structs to pad them to word alignment.
+ *
+ * Technically this is non-compliant, BROKEN_UNALIGNED should *only*
+ * be defined on archs that cannot do unaligned accesses.
+ */
+
+#ifdef BROKEN_UNALIGNED
+#  define EFI_DP_PAD(n)  u8 __pad[n]
+#else
+#  define EFI_DP_PAD(n)
+#endif
+
 struct efi_device_path {
 	u8 type;
 	u8 sub_type;
@@ -318,12 +343,14 @@ struct efi_device_path_usb {
 	struct efi_device_path dp;
 	u8 parent_port_number;
 	u8 usb_interface;
+	EFI_DP_PAD(2);
 } __packed;
 
 struct efi_device_path_mac_addr {
 	struct efi_device_path dp;
 	struct efi_mac_addr mac;
 	u8 if_type;
+	EFI_DP_PAD(3);
 } __packed;
 
 struct efi_device_path_usb_class {
@@ -333,11 +360,13 @@ struct efi_device_path_usb_class {
 	u8 device_class;
 	u8 device_subclass;
 	u8 device_protocol;
+	EFI_DP_PAD(1);
 } __packed;
 
 struct efi_device_path_sd_mmc_path {
 	struct efi_device_path dp;
 	u8 slot_number;
+	EFI_DP_PAD(3);
 } __packed;
 
 #define DEVICE_PATH_TYPE_MEDIA_DEVICE		0x04
@@ -353,6 +382,7 @@ struct efi_device_path_hard_drive_path {
 	u8 partition_signature[16];
 	u8 partmap_type;
 	u8 signature_type;
+	EFI_DP_PAD(1);
 } __packed;
 
 struct efi_device_path_cdrom_path {
diff --git a/lib/efi_loader/efi_device_path.c b/lib/efi_loader/efi_device_path.c
index b5acf73f98..515a1f4737 100644
--- a/lib/efi_loader/efi_device_path.c
+++ b/lib/efi_loader/efi_device_path.c
@@ -402,6 +402,9 @@ struct efi_device_path *efi_dp_from_file(struct blk_desc *desc, int part,
 
 	// TODO efi_device_path_file_path should be variable length:
 	fpsize = sizeof(struct efi_device_path) + 2 * (strlen(path) + 1);
+#ifdef BROKEN_UNALIGNED
+	fpsize = ALIGN(fpsize, 4);
+#endif
 	dpsize += fpsize;
 
 	start = buf = calloc(1, dpsize + sizeof(END));
-- 
2.13.0