efi_loader: Fix warnings for unaligned accesses

Tom reports that when building with clang we see this warning:
field guid within 'struct efi_hii_keyboard_layout' is less aligned than 'efi_guid_t' and is usually due to 'struct efi_hii_keyboard_layout' being packed, which can lead to unaligned accesses [-Wunaligned-access]

This happens because 'struct efi_hii_keyboard_layout' is defined as
packed and thus has 1-byte alignment but efi_guid_t is a type that
requires greater alignment than that.

However the EFI spec describes the EFI_GUID as
"128-bit buffer containing a unique identifier value.
Unless otherwise specified"

So convert the efi_guid_t -> u8 b[16] here and skip the alignment
requirements.  Since the struct is packed to begin with, it makes no
difference on the final memory layout.

Suggested-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reported-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

diff --git a/include/efi_api.h b/include/efi_api.h
index 2fd0221c1c77b8da58d8e49cbee6888af215bf32..55a4c989fc7c4b04e8415eb2db578c8a888e789c 100644 (file)
--- a/include/efi_api.h
+++ b/include/efi_api.h
@@ -1170,7 +1170,33 @@ struct efi_key_descriptor {
 
 struct efi_hii_keyboard_layout {
        u16 layout_length;
-       efi_guid_t guid;
+       /*
+        * The EFI spec defines this as efi_guid_t.
+        * clang and gcc both report alignment problems here.
+        * clang with -Wunaligned-access
+        * warning: field guid within 'struct efi_hii_keyboard_layout' is less
+        * aligned than 'efi_guid_t' and is usually due to
+        * 'struct efi_hii_keyboard_layout' being packed, which can lead to
+        * unaligned accesses
+        *
+        * GCC with -Wpacked-not-aligned -Waddress-of-packed-member
+        * 'efi_guid_t' offset 2 in 'struct efi_hii_keyboard_layout'
+        * isn't aligned to 4
+        *
+        * Removing the alignment from efi_guid_t is not an option, since
+        * it is also used in non-packed structs and that would break
+        * calculations with offsetof
+        *
+        * This is the only place we get a report for. That happens because
+        * all other declarations of efi_guid_t within a packed struct happens
+        * to be 4-byte aligned.  i.e a u32, a u64 a 2 * u16 or any combination
+        * that ends up landing efi_guid_t on a 4byte boundary precedes.
+        *
+        * Replace this with a 1-byte aligned counterpart of b[16].  This is a
+        * packed struct so the memory  placement of efi_guid_t should not change
+        *
+        */
+       u8 guid[16];
        u32 layout_descriptor_string_offset;
        u8 descriptor_count;
        /* struct efi_key_descriptor descriptors[]; follows here */