x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI_STUB

[PATCH] x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI_STUB

Posted by Nathan Chancellor 3 years, 2 months ago

A recent change in LLVM made CONFIG_EFI_STUB unselectable because it no
longer pretends to support '-mabi=ms', breaking the dependency in
Kconfig. Lack of CONFIG_EFI_STUB can prevent kernels from booting via
EFI in certain circumstances.

This check was added by commit 8f24f8c2fc82 ("efi/libstub: Annotate
firmware routines as __efiapi") to ensure that '__attribute__((ms_abi))'
was available, as '-mabi=ms' is not actually used in any cflags.
According to the GCC documentation, this attribute has been supported
since GCC 4.4.7. The kernel currently requires GCC 5.1 so this check is
not necessary; even when that change landed in 5.6, the kernel required
GCC 4.9 so it was unnecessary then as well.  Clang supports
'__attribute__((ms_abi))' for all versions that are supported for
building the kernel so no additional check is needed. Remove the
'depends on' line altogether to allow CONFIG_EFI_STUB to be selected
when CONFIG_EFI is enabled, regardless of compiler.

Cc: stable@vger.kernel.org
Fixes: 8f24f8c2fc82 ("efi/libstub: Annotate firmware routines as __efiapi")
Link: https://github.com/ClangBuiltLinux/linux/issues/1725
Link: https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Function-Attributes.html
Link: https://github.com/llvm/llvm-project/commit/d1ad006a8f64bdc17f618deffa9e7c91d82c444d
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/x86/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f9920f1341c8..81012154d9ed 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1956,7 +1956,6 @@ config EFI
 config EFI_STUB
 	bool "EFI stub support"
 	depends on EFI
-	depends on $(cc-option,-mabi=ms) || X86_32
 	select RELOCATABLE
 	help
 	  This kernel feature allows a bzImage to be loaded directly

base-commit: f76349cf41451c5c42a99f18a9163377e4b364ff
-- 
2.37.3

Re: [PATCH] x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI_STUB

Posted by Ard Biesheuvel 3 years, 1 month ago

On Thu, 29 Sept 2022 at 17:20, Nathan Chancellor <nathan@kernel.org> wrote:
>
> A recent change in LLVM made CONFIG_EFI_STUB unselectable because it no
> longer pretends to support '-mabi=ms', breaking the dependency in
> Kconfig. Lack of CONFIG_EFI_STUB can prevent kernels from booting via
> EFI in certain circumstances.
>
> This check was added by commit 8f24f8c2fc82 ("efi/libstub: Annotate
> firmware routines as __efiapi") to ensure that '__attribute__((ms_abi))'
> was available, as '-mabi=ms' is not actually used in any cflags.
> According to the GCC documentation, this attribute has been supported
> since GCC 4.4.7. The kernel currently requires GCC 5.1 so this check is
> not necessary; even when that change landed in 5.6, the kernel required
> GCC 4.9 so it was unnecessary then as well.  Clang supports
> '__attribute__((ms_abi))' for all versions that are supported for
> building the kernel so no additional check is needed. Remove the
> 'depends on' line altogether to allow CONFIG_EFI_STUB to be selected
> when CONFIG_EFI is enabled, regardless of compiler.
>
> Cc: stable@vger.kernel.org
> Fixes: 8f24f8c2fc82 ("efi/libstub: Annotate firmware routines as __efiapi")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1725
> Link: https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Function-Attributes.html
> Link: https://github.com/llvm/llvm-project/commit/d1ad006a8f64bdc17f618deffa9e7c91d82c444d
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Acked-by: Ard Biesheuvel <ardb@kernel.org>

I can take this as a EFI fix as well.

> ---
>  arch/x86/Kconfig | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..81012154d9ed 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1956,7 +1956,6 @@ config EFI
>  config EFI_STUB
>         bool "EFI stub support"
>         depends on EFI
> -       depends on $(cc-option,-mabi=ms) || X86_32
>         select RELOCATABLE
>         help
>           This kernel feature allows a bzImage to be loaded directly
>
> base-commit: f76349cf41451c5c42a99f18a9163377e4b364ff
> --
> 2.37.3
>

Re: [PATCH] x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI_STUB

Posted by Nathan Chancellor 3 years, 1 month ago

Hi x86 folks,

Would it be possible to pick this up for 6.1 so it can start filtering
into the stable trees? I know it came down towards the beginning of the
merge window so I understand the silence but I have had a couple of
people independently report this problem when they used a newer snapshot
of LLVM. This problem is not immediately obvious if you do not have a
previous configuration to diff against.

Cheers,
Nathan

On Thu, Sep 29, 2022 at 08:20:10AM -0700, Nathan Chancellor wrote:
> A recent change in LLVM made CONFIG_EFI_STUB unselectable because it no
> longer pretends to support '-mabi=ms', breaking the dependency in
> Kconfig. Lack of CONFIG_EFI_STUB can prevent kernels from booting via
> EFI in certain circumstances.
> 
> This check was added by commit 8f24f8c2fc82 ("efi/libstub: Annotate
> firmware routines as __efiapi") to ensure that '__attribute__((ms_abi))'
> was available, as '-mabi=ms' is not actually used in any cflags.
> According to the GCC documentation, this attribute has been supported
> since GCC 4.4.7. The kernel currently requires GCC 5.1 so this check is
> not necessary; even when that change landed in 5.6, the kernel required
> GCC 4.9 so it was unnecessary then as well.  Clang supports
> '__attribute__((ms_abi))' for all versions that are supported for
> building the kernel so no additional check is needed. Remove the
> 'depends on' line altogether to allow CONFIG_EFI_STUB to be selected
> when CONFIG_EFI is enabled, regardless of compiler.
> 
> Cc: stable@vger.kernel.org
> Fixes: 8f24f8c2fc82 ("efi/libstub: Annotate firmware routines as __efiapi")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1725
> Link: https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Function-Attributes.html
> Link: https://github.com/llvm/llvm-project/commit/d1ad006a8f64bdc17f618deffa9e7c91d82c444d
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  arch/x86/Kconfig | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..81012154d9ed 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1956,7 +1956,6 @@ config EFI
>  config EFI_STUB
>  	bool "EFI stub support"
>  	depends on EFI
> -	depends on $(cc-option,-mabi=ms) || X86_32
>  	select RELOCATABLE
>  	help
>  	  This kernel feature allows a bzImage to be loaded directly
> 
> base-commit: f76349cf41451c5c42a99f18a9163377e4b364ff
> -- 
> 2.37.3
> 
>

Re: [PATCH] x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI_STUB

Posted by Nick Desaulniers 3 years, 2 months ago

On Thu, Sep 29, 2022 at 8:20 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> A recent change in LLVM made CONFIG_EFI_STUB unselectable because it no
> longer pretends to support '-mabi=ms', breaking the dependency in
> Kconfig. Lack of CONFIG_EFI_STUB can prevent kernels from booting via
> EFI in certain circumstances.
>
> This check was added by commit 8f24f8c2fc82 ("efi/libstub: Annotate
> firmware routines as __efiapi") to ensure that '__attribute__((ms_abi))'
> was available, as '-mabi=ms' is not actually used in any cflags.
> According to the GCC documentation, this attribute has been supported
> since GCC 4.4.7. The kernel currently requires GCC 5.1 so this check is
> not necessary; even when that change landed in 5.6, the kernel required
> GCC 4.9 so it was unnecessary then as well.  Clang supports
> '__attribute__((ms_abi))' for all versions that are supported for
> building the kernel so no additional check is needed. Remove the
> 'depends on' line altogether to allow CONFIG_EFI_STUB to be selected
> when CONFIG_EFI is enabled, regardless of compiler.
>
> Cc: stable@vger.kernel.org
> Fixes: 8f24f8c2fc82 ("efi/libstub: Annotate firmware routines as __efiapi")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1725
> Link: https://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Function-Attributes.html
> Link: https://github.com/llvm/llvm-project/commit/d1ad006a8f64bdc17f618deffa9e7c91d82c444d
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/x86/Kconfig | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f9920f1341c8..81012154d9ed 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1956,7 +1956,6 @@ config EFI
>  config EFI_STUB
>         bool "EFI stub support"
>         depends on EFI
> -       depends on $(cc-option,-mabi=ms) || X86_32
>         select RELOCATABLE
>         help
>           This kernel feature allows a bzImage to be loaded directly
>
> base-commit: f76349cf41451c5c42a99f18a9163377e4b364ff
> --
> 2.37.3
>


-- 
Thanks,
~Nick Desaulniers