Akashi-san On Fri, 7 Apr 2023 at 10:33, Ilias Apalodimas <ilias.apalodi...@linaro.org> wrote: > > On Fri, 7 Apr 2023 at 04:46, AKASHI Takahiro <takahiro.aka...@linaro.org> > wrote: > > > > 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. > > I assumed that all other definitions are aligned regardless of packed, > i.e they are defined right after a u32, u64, 2xu16 etc, but I'll have > a closer look
So I did look closer and my assumption was indeed correct. IOW the warning is the only place in the struct definition where efi_guid_t happens to be be aligned. Tom would you like me to send a v2 on this? I think what happens here is that struct efi_hii_keyboard_layout is defined as packed, and efi_guid_t is aligned(4). So clang is trying to tell us: I will generate safe code for unaligned accesses, but one of the struct members requires specific alignment. Regards /Ilias > > > > > > 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.) > > commit 1dd705cf9903 ("efi: use 32-bit alignment for efi_guid_t") > explains why, but it's a bit orthogonal to this commit. In any case > I'll include it in v2 > > Thanks > /Ilias > > > > -Takahiro Akashi > > > > > > > > So convert the efi_guid_t -> u8 b[16] here and skip the alignment > > > requirements. > > > > > > Reported-by: Tom Rini <tr...@konsulko.com> > > > Suggested-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com> > > > Signed-off-by: Ilias Apalodimas <ilias.apalodi...@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 > > >