[PATCH v2] efi_loader: Fix warnings for unaligned accesses
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
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.
Commit messages should preferably limited to 75 characters per line, see scripts/checkpatch.pl. No need to resubmit.
Reviewed-by: Heinrich Schuchardt xypron.glpk@gmx.de
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
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 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];
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
-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 xypron.glpk@gmx.de
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 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];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 xypron.glpk@gmx.de
participants (3)
-
AKASHI Takahiro -
Heinrich Schuchardt -
Ilias Apalodimas