linux-kernel - [PATCH] x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI

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Message-Id: <20220929152010.835906-1-nathan@kernel.org>
Date:   Thu, 29 Sep 2022 08:20:10 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev,
        Nathan Chancellor <nathan@...nel.org>, stable@...r.kernel.org
Subject: [PATCH] x86/Kconfig: Drop check for '-mabi=ms' for CONFIG_EFI_STUB

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@...r.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@...nel.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