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Message-ID: <5f9d3aa5fad957dae2f14e483b3b79dbcf9e794d.camel@xry111.site>
Subject: Re: [PATCH v6 3/6] LoongArch: Use model("extreme") attribute for
 per-CPU variables in module if CONFIG_AS_HAS_EXPLICIT_RELOCS
From:   Xi Ruoyao <xry111@xry111.site>
To:     loongarch@lists.linux.dev
Cc:     linux-kernel@vger.kernel.org, WANG Xuerui <kernel@xen0n.name>,
        Huacai Chen <chenhuacai@kernel.org>,
        Youling Tang <tangyouling@loongson.cn>,
        Jinyang He <hejinyang@loongson.cn>
Date:   Mon, 29 Aug 2022 23:02:40 +0800
In-Reply-To: <20220829133146.15236-4-xry111@xry111.site>
References: <20220829133146.15236-1-xry111@xry111.site>
         <20220829133146.15236-4-xry111@xry111.site>
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On Mon, 2022-08-29 at 21:31 +0800, Xi Ruoyao wrote:
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 1563747c4fa8..593818a61741 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -53,6 +53,9 @@ LDFLAGS_vmlinux=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0+=3D -G0 -static -n -nostdlib
> =C2=A0# combination of a "new" assembler and "old" compiler is not suppor=
ted.=C2=A0 Either
> =C2=A0# upgrade the compiler or downgrade the assembler.
> =C2=A0ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS
> +ifeq ($(shell echo '__has_attribute(model)' | $(CC) -E -P - 2> /dev/null=
), 0)
> +$(error "C compiler must support model attribute if using explicit reloc=
s")
> +endif

Self review:

I'm wondering if we really need this thing...  There won't be a GCC
version released with explicit relocation but without model attribute
(GCC 13 starts to support them both).

But without a check, if someone uses an early GCC 13 snapshot and
ignores the -Wattributes warning, the system will suddenly blow up
loading a module with per-CPU variable defined.

Maybe "-Werror=3Dattributes" is better, but is it OK to add a -Werror=3D
option for entire Linux tree?

> =C2=A0cflags-y=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0+=3D -mexplicit-relocs
> =C2=A0else
> =C2=A0cflags-y=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0+=3D $(call cc-option,-mno-explicit-relocs)

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University