From: Arnd Bergmann <arnd@kernel.org>
To: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
clang-built-linux <llvm@lists.linux.dev>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Tom Rix <trix@redhat.com>
Subject: Re: [RESEND PATCH v1] x86/build: add -fno-builtin flag to prevent shadowing
Date: Sun, 8 May 2022 12:27:49 +0200 [thread overview]
Message-ID: <CAK8P3a3Fw2T0WSkxv4DiTG2wGkKcs24StPx-BG_vi=ffa9OLVA@mail.gmail.com> (raw)
In-Reply-To: <20220508100907.61231-1-mailhol.vincent@wanadoo.fr>
On Sun, May 8, 2022 at 12:09 PM Vincent Mailhol
<mailhol.vincent@wanadoo.fr> wrote:
>
> Aside of the __builtin_foo() ones, x86 does not directly rely on any
> builtin functions.
>
> However, such builtin functions are not explicitly deactivated,
> creating some collisions, concrete example being ffs() from bitops.h,
> c.f.:
>
> | ./arch/x86/include/asm/bitops.h:283:28: warning: declaration of 'ffs' shadows a built-in function [-Wshadow]
> | 283 | static __always_inline int ffs(int x)
>
> This patch adds -fno-builtin to KBUILD_CFLAGS for the x86
> architectures in order to prevent shadowing of builtin functions.
>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> ---
> FYI, I tested this patch on a "make allyesconfig" for both x86_32 and
> x86_64.
>
> This is a resend. Only difference is that I dropped the RFC flag and
> added Arnd in CC because he did a similar patch to fix ffs shadow
> warnings in the past:
>
> https://lore.kernel.org/all/20201026160006.3704027-1-arnd@kernel.org/
I think this is a correct change, but unfortunately it exposes a clang bug
with -mregparm=3. Nick should be able to provide more details, I think
he has a plan.
> ---
> arch/x86/Makefile | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index e84cdd409b64..5ff7b6571dd2 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -53,6 +53,8 @@ export REALMODE_CFLAGS
> # e.g.: obj-y += foo_$(BITS).o
> export BITS
>
> +KBUILD_CFLAGS += -fno-builtin
> +
> #
> # Prevent GCC from generating any FP code by mistake.
> #
> --
> 2.34.1
>
next prev parent reply other threads:[~2022-05-08 10:28 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-06 17:10 [RFC PATCH v1] x86/build: add -fno-builtin flag to prevent shadowing Vincent Mailhol
2022-05-08 10:09 ` [RESEND " Vincent Mailhol
2022-05-08 10:27 ` Arnd Bergmann [this message]
2022-05-08 12:37 ` Vincent MAILHOL
2022-05-08 23:51 ` Nathan Chancellor
2022-05-09 15:00 ` Vincent MAILHOL
2022-05-09 19:50 ` Nick Desaulniers
2022-05-09 23:12 ` Vincent MAILHOL
2022-05-09 23:26 ` Nick Desaulniers
2022-05-10 1:10 ` Vincent MAILHOL
2022-05-10 14:33 ` Vincent MAILHOL
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