[PATCH 2/2] efi_loader: Fix warnings on unaligned accesses
AKASHI Takahiro
takahiro.akashi at linaro.org
Fri Apr 7 03:46:08 CEST 2023
Hi Ilias,
On Thu, Apr 06, 2023 at 10:37:07PM +0300, Ilias Apalodimas wrote:
> 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 while efi_guid_t is 32bit aligned.
There are a couple of 'struct' definitions which are *packed*
and contain an 'efi_guid_t' member in efi_api.h.
If 'efi_hii_keyboard_layout' is the only place that causes a clang warning,
we need a more specific explanation to clarify the problem.
> However the EFI spec describes the EFI_GUID as
> "128-bit buffer containing a unique identifier value.
> Unless otherwise specified aligned on a 64-bit boundary"
That's right, but this text in this context may sound misleading.
(It doesn't explain why 'efi_guid_t' is 32-bit aligned.)
-Takahiro Akashi
>
> So convert the efi_guid_t -> u8 b[16] here and skip the alignment
> requirements.
>
> Reported-by: Tom Rini <trini at konsulko.com>
> Suggested-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> ---
> include/efi_api.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/efi_api.h b/include/efi_api.h
> index 2fd0221c1c77..b84b577bd7b5 100644
> --- a/include/efi_api.h
> +++ b/include/efi_api.h
> @@ -1170,7 +1170,7 @@ struct efi_key_descriptor {
>
> struct efi_hii_keyboard_layout {
> u16 layout_length;
> - efi_guid_t guid;
> + u8 guid[16];
> u32 layout_descriptor_string_offset;
> u8 descriptor_count;
> /* struct efi_key_descriptor descriptors[]; follows here */
> --
> 2.39.2
>
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