Hi Heinrich, On Thu, 11 May 2023 at 19:56, Heinrich Schuchardt <[email protected]> wrote: > > On 5/11/23 18:40, 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 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 <[email protected]> > > Reported-by: Tom Rini <[email protected]> > > Signed-off-by: Ilias Apalodimas <[email protected]> > > --- > > 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 > > > > Thank you for investigating this in depth.
yw :) > > Commit messages should preferably limited to 75 characters per line, see > scripts/checkpatch.pl. No need to resubmit. Yea I know, I just prefered to keep the clang warning intact in the commit message Thanks /Ilias > > Reviewed-by: Heinrich Schuchardt <[email protected]>
