[PATCH 02/18] efi: define efi_guid_t as 32-bit aligned guid_t

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Let's sync definition with Linux, so we are able to pass efi_guid_t
types to function accepting guid_t. This has the added benefit of us
starting to observe alignment, which may become relevant with barebox
EFI on non-x86.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 include/efi.h | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/efi.h b/include/efi.h
index 3595cf05ccb7..1904caf3a4b6 100644
--- a/include/efi.h
+++ b/include/efi.h
@@ -14,6 +14,7 @@
  */
 #include <linux/string.h>
 #include <linux/types.h>
+#include <linux/uuid.h>
 
 #ifdef CONFIG_EFI_BOOTUP
 #define EFIAPI __attribute__((ms_abi))
@@ -66,10 +67,20 @@ typedef u16 efi_char16_t;		/* UNICODE character */
 typedef u64 efi_physical_addr_t;
 typedef void *efi_handle_t;
 
-
-typedef struct {
-	u8 b[16];
-} efi_guid_t;
+/*
+ * The UEFI spec and EDK2 reference implementation both define EFI_GUID as
+ * struct { u32 a; u16; b; u16 c; u8 d[8]; }; and so the implied alignment
+ * is 32 bits not 8 bits like our guid_t. In some cases (i.e., on 32-bit ARM),
+ * this means that firmware services invoked by the kernel may assume that
+ * efi_guid_t* arguments are 32-bit aligned, and use memory accessors that
+ * do not tolerate misalignment. So let's set the minimum alignment to 32 bits.
+ *
+ * Note that the UEFI spec as well as some comments in the EDK2 code base
+ * suggest that EFI_GUID should be 64-bit aligned, but this appears to be
+ * a mistake, given that no code seems to exist that actually enforces that
+ * or relies on it.
+ */
+typedef guid_t efi_guid_t __aligned(__alignof__(u32));
 
 #define EFI_GUID(a, b, c, d0, d1, d2, d3, d4, d5, d6, d7) \
 ((efi_guid_t) \
-- 
2.39.2