linux-kernel - Re: [PATCH v6 3/6] LoongArch: Use model("extreme") attribute for per-CPU variables in module if CONFIG_AS_HAS_EXPLICIT

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Date:   Mon, 29 Aug 2022 23:06:58 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Xi Ruoyao <xry111@...111.site>
Cc:     loongarch@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Youling Tang <tangyouling@...ngson.cn>,
        Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH v6 3/6] LoongArch: Use model("extreme") attribute for
 per-CPU variables in module if CONFIG_AS_HAS_EXPLICIT_RELOCS

Hi, Ruoyao,

On Mon, Aug 29, 2022 at 11:02 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> 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                       += -G0 -static -n -nostdlib
> >  # combination of a "new" assembler and "old" compiler is not supported.  Either
> >  # upgrade the compiler or downgrade the assembler.
> >  ifdef 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 relocs")
> > +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=attributes" is better, but is it OK to add a -Werror=
> option for entire Linux tree?
I think we can remove it entirely, and then this patch seems can be
squashed into patch 2.

Huacai
>
> >  cflags-y                       += -mexplicit-relocs
> >  else
> >  cflags-y                       += $(call cc-option,-mno-explicit-relocs)
>
> --
> Xi Ruoyao <xry111@...111.site>
> School of Aerospace Science and Technology, Xidian University
>