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 --- Changes since v1: - Adjust the commit message and add a comment on why this happens
include/efi_api.h | 28 +++++++++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/include/efi_api.h b/include/efi_api.h index 2fd0221c1c77..55a4c989fc7c 100644 --- 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 */ -- 2.39.2