Akashi-san, On Fri, May 12, 2023 at 09:05:05AM +0900, AKASHI Takahiro wrote: > Hi Ilias, > > On Thu, May 11, 2023 at 08:00:32PM +0300, Ilias Apalodimas wrote: > > 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]; > > I thought that you have agreed with my comment, saying keep "efi_guid_t" here. > https://lists.denx.de/pipermail/u-boot/2023-April/515831.html
I changed my mind since then since keeping efi_guid_t is indeed a problem, so i won't silence that. The compiler might emit code with memory instructions that don't tolerate misalignment What we could do if we get more than one structs is add a efi_guid_ua_t which wont have the alignment requirements and use that. Regards /Ilias > > -Takahiro Akashi > > > > > > 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]>
