From: Nathan Chancellor <nathan@kernel.org>
To: Kees Cook <kees@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"Mike Rapoport (Microsoft)" <rppt@kernel.org>,
Pratyush Yadav <ptyadav@amazon.de>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Coiby Xu <coxu@redhat.com>, Josh Poimboeuf <jpoimboe@kernel.org>,
Alexander Graf <graf@amazon.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH] kstack_erase: Add -mgeneral-regs-only to silence Clang warnings
Date: Sun, 27 Jul 2025 08:51:08 -0700 [thread overview]
Message-ID: <20250727155108.GB1183915@ax162> (raw)
In-Reply-To: <20250726212615.work.800-kees@kernel.org>
On Sat, Jul 26, 2025 at 02:26:19PM -0700, Kees Cook wrote:
> Once CONFIG_KSTACK_ERASE is enabled with Clang on i386, the build warns:
>
> kernel/kstack_erase.c:168:2: warning: function with attribute 'no_caller_saved_registers' should only call a function with attribute 'no_caller_saved_registers' or be compiled with '-mgeneral-regs-only' [-Wexcessive-regsave]
>
> Add -mgeneral-regs-only for the kstack_erase handler, to make Clang feel
> better (it is effectively a no-op flag for the kernel). No binary
> changes encountered.
>
> Build & boot tested with Clang 21 on x86_64, and i386.
> Build tested with GCC 14.2.0 on x86_64, i386, arm64, and arm.
>
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Closes: https://lore.kernel.org/all/20250726004313.GA3650901@ax162
> Signed-off-by: Kees Cook <kees@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
> ---
> kernel/Makefile | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/Makefile b/kernel/Makefile
> index e4f01f1d4d0c..0ee9afd8b7cf 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -140,6 +140,7 @@ obj-$(CONFIG_RESOURCE_KUNIT_TEST) += resource_kunit.o
> obj-$(CONFIG_SYSCTL_KUNIT_TEST) += sysctl-test.o
>
> CFLAGS_kstack_erase.o += $(DISABLE_KSTACK_ERASE)
> +CFLAGS_kstack_erase.o += $(call cc-option,-mgeneral-regs-only)
> obj-$(CONFIG_KSTACK_ERASE) += kstack_erase.o
> KASAN_SANITIZE_kstack_erase.o := n
> KCSAN_SANITIZE_kstack_erase.o := n
> --
> 2.34.1
>
prev parent reply other threads:[~2025-07-27 15:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-26 21:26 Kees Cook
2025-07-27 15:51 ` Nathan Chancellor [this message]
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