linux-kernel - Re: [PATCH] LoongArch: Drop -ffreestanding from CFLAGS

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Message-ID: <CAAhV-H5g-jmeQMhicrqhpStV9n0Z-EZ1dZAsuT2hmOaHki4ucg@mail.gmail.com>
Date:   Fri, 4 Aug 2023 23:25:50 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     WANG Xuerui <kernel@...0n.name>
Cc:     Nathan Chancellor <nathan@...nel.org>, loongarch@...ts.linux.dev,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        WANG Xuerui <git@...0n.name>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] LoongArch: Drop -ffreestanding from CFLAGS

Hi, Xuerui,

On Fri, Aug 4, 2023 at 8:56 PM WANG Xuerui <kernel@...0n.name> wrote:
>
> From: WANG Xuerui <git@...0n.name>
>
> As explained by Nick in the original issue: the kernel usually does a
> good job of providing library helpers that have similar semantics as
> their ordinary userspace libc equivalents, but -ffreestanding disables
> such libcall optimization and other related features in the compiler,
> which can lead to unexpected things such as CONFIG_FORTIFY_SOURCE not
> working (!).
>
> As it turns out to be the case, removing the flag does not impact the
> LoongArch kernel's normal operation at all; so just remove it to
> restore expected libcall semantics globally on this architecture.
>
Not all processors support unaligned access, so we need the
alternative mechanism to select memset/memcpy/memmove implementations.
If remove -ffreestanding, the builtin implementation cannot be used on
all hardware.

Huacai

> Closes: https://github.com/ClangBuiltLinux/linux/issues/1897
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: WANG Xuerui <git@...0n.name>
> ---
>  arch/loongarch/Makefile | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index b1e5db51b61c..db0d7210272d 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -83,7 +83,6 @@ KBUILD_CFLAGS_KERNEL          += -fPIE
>  LDFLAGS_vmlinux                        += -static -pie --no-dynamic-linker -z notext
>  endif
>
> -cflags-y += -ffreestanding
>  cflags-y += $(call cc-option, -mno-check-zero-division)
>
>  load-y         = 0x9000000000200000
> --
> 2.40.0
>