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efi_loader: Fix warnings for unaligned accesses

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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>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
This commit is contained in:
Ilias Apalodimas 2023-05-11 19:40:35 +03:00 committed by Heinrich Schuchardt
parent 227d3b3e0a
commit 7dfab39855
1 changed files with 27 additions and 1 deletions
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28
include/efi_api.h
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@ -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 */