On Thu, 20 Apr 2023 at 10:16, AKASHI Takahiro takahiro.akashi@linaro.org wrote:
On Thu, Apr 20, 2023 at 09:35:42AM +0300, Ilias Apalodimas wrote:
Akashi-san
On Fri, 7 Apr 2023 at 10:33, Ilias Apalodimas ilias.apalodimas@linaro.org wrote:
On Fri, 7 Apr 2023 at 04:46, AKASHI Takahiro takahiro.akashi@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.
My concern is that we use char[] in one place and efi_guid_t elsewhere. It sounds arbitrary without any clear explanation.
I can send a v2 adding a comment, but I changed my mind as well. I think explicitly disabling the warning in such places (as Tom did on his original patch) is a better solution. We still have to add a comment about why, but I'd prefer keeping a consistent efi_guid_t as well
Regards /Ilias
-Takahiro Akashi
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 trini@konsulko.com Suggested-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com Signed-off-by: Ilias Apalodimas ilias.apalodimas@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