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SubjectRe: [PATCH] x86/Kconfig: Fix CONFIG_CC_HAS_SANE_STACKPROTECTOR when cross compiling with clang
Gentle ping for review.

On Fri, Jun 17, 2022 at 11:08:46AM -0700, Nathan Chancellor wrote:
> Chimera Linux notes that CONFIG_CC_HAS_SANE_STACKPROTECTOR cannot be
> enabled when cross compiling an x86_64 kernel with clang, even though it
> does work when natively compiling.
>
> When building on aarch64:
>
> $ make -sj"$(nproc)" ARCH=x86_64 LLVM=1 defconfig
>
> $ grep STACKPROTECTOR .config
>
> When building on x86_64:
>
> $ make -sj"$(nproc)" ARCH=x86_64 LLVM=1 defconfig
>
> $ grep STACKPROTECTOR .config
> CONFIG_CC_HAS_SANE_STACKPROTECTOR=y
> CONFIG_HAVE_STACKPROTECTOR=y
> CONFIG_STACKPROTECTOR=y
> CONFIG_STACKPROTECTOR_STRONG=y
>
> When clang is invoked without a '--target' flag, code is generated for
> the default target, which is usually the host (it is configurable via
> cmake). As a result, the has-stack-protector scripts will generate code
> for the default target but check for x86 specific segment registers,
> which cannot succeed if the default target is not x86.
>
> $(CLANG_FLAGS) contains an explicit '--target' flag so pass that
> variable along to the has-stack-protector scripts so that the stack
> protector can be enabled when cross compiling with clang. The 32-bit
> stack protector cannot currently be enabled with clang, as it does not
> support '-mstack-protector-guard-symbol', so this results in no
> functional change for ARCH=i386 when cross compiling.
>
> Link: https://github.com/chimera-linux/cports/commit/0fb7e506d5f83fdf2104feb22cdac34934561226
> Link: https://github.com/llvm/llvm-project/issues/48553
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>
> Fixes: 2a61f4747eea ("stack-protector: test compiler capability in Kconfig and drop AUTO mode")
>
> might be appropriate; I am conflicted on fixes tags for problems that
> that arise due to use cases that were not considered at the time of a
> change, as it feels wrong to blame the commit for not looking far enough
> into the future where it might be common for people to have workstations
> running another architecture other than x86_64.
>
> Chimera appears to use a 5.15 kernel so a
>
> Cc: stable@vger.kernel.org
>
> might be nice but some maintainers are picky about that so I leave it up
> to you all.
>
> arch/x86/Kconfig | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index be0b95e51df6..076adde7ead9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -391,8 +391,8 @@ config PGTABLE_LEVELS
>
> config CC_HAS_SANE_STACKPROTECTOR
> bool
> - default $(success,$(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC)) if 64BIT
> - default $(success,$(srctree)/scripts/gcc-x86_32-has-stack-protector.sh $(CC))
> + default $(success,$(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC) $(CLANG_FLAGS)) if 64BIT
> + default $(success,$(srctree)/scripts/gcc-x86_32-has-stack-protector.sh $(CC) $(CLANG_FLAGS))
> help
> We have to make sure stack protector is unconditionally disabled if
> the compiler produces broken code or if it does not let us control
>
> base-commit: b13baccc3850ca8b8cccbf8ed9912dbaa0fdf7f3
> --
> 2.36.1
>
>

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