linux-kernel - Re: [PATCH V4 19/22] LoongArch: Add VDSO and VSYSCALL support

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Date:   Sat, 2 Oct 2021 20:44:16 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     Xi Ruoyao <xry111@...gyan1223.wang>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Airlie <airlied@...ux.ie>,
        Jonathan Corbet <corbet@....net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Yanteng Si <siyanteng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V4 19/22] LoongArch: Add VDSO and VSYSCALL support

Hi, Ruoyao,

On Sat, Oct 2, 2021 at 8:14 PM Xi Ruoyao <xry111@...gyan1223.wang> wrote:
>
> On Sat, 2021-10-02 at 18:53 +0800, Huacai Chen wrote:
> > Hi, Ruoyao,
> >
> > On Thu, Sep 30, 2021 at 11:43 PM Xi Ruoyao <xry111@...gyan1223.wang>
> > wrote:
> > >
> > > On Mon, 2021-09-27 at 14:42 +0800, Huacai Chen wrote:
> > > > diff --git a/arch/loongarch/vdso/gen_vdso_offsets.sh
> > > > b/arch/loongarch/vdso/gen_vdso_offsets.sh
> > > > new file mode 100755
> > > > index 000000000000..7da255fea213
> > > > --- /dev/null
> > > > +++ b/arch/loongarch/vdso/gen_vdso_offsets.sh
> > > > @@ -0,0 +1,14 @@
> > > > +#!/bin/sh
> > > > +# SPDX-License-Identifier: GPL-2.0
> > > > +
> > > > +#
> > > > +# Derived from RISC-V and ARM64:
> > > > +# Author: Will Deacon <will.deacon@....com>
> > > > +#
> > > > +# Match symbols in the DSO that look like VDSO_*; produce a
> > > > header
> > > > file
> > > > +# of constant offsets into the shared object.
> > > > +#
> > > > +
> > > > +LC_ALL=C
> > >
> > > I'm wondering whether this line is really useful... There is no
> > > "export"
> > > here so the variable won't be passed to the environment of the sed
> > > command below.
> > Have you encountered some problems with this? It just works for me,
> > and both ARM64 and RISCV are the same.
>
> No problems, and I also seen those in ARM64 & RISCV.  But AFAIK this
> line really does nothing and can be removed.
>
> If LC_ALL=C is really necessary for the sed to operate correctly, it
> should be "exported" as
>
> LC_ALL=C
> export LC_ALL
>
> ("export LC_ALL=C" will work under bash, but it's not POSIX.)
>
> Or, explicitly pass LC_ALL to sed with:
>
> LC_ALL=C sed ...
OK, I think this way is better. Thanks.

Huacai
> --
> Xi Ruoyao <xry111@...gyan1223.wang>
> School of Aerospace Science and Technology, Xidian University