Hi Heinrich,
On Thu, 11 May 2023 at 19:56, Heinrich Schuchardt xypron.glpk@gmx.de 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 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
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 xypron.glpk@gmx.de