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Message-ID: <4df8a26c49a35c1fce36d80c370f738fa71a2bef.camel@xry111.site>
Subject: Re: [PATCH 1/3] LoongArch: tools: Add relocs tool support
From:   Xi Ruoyao <xry111@xry111.site>
To:     Youling Tang <tangyouling@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>
Cc:     linux-kernel@vger.kernel.org, loongarch@lists.linux.dev,
        Xuerui Wang <kernel@xen0n.name>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>
Date:   Fri, 02 Sep 2022 19:27:28 +0800
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On Fri, 2022-09-02 at 19:10 +0800, Xi Ruoyao wrote:
> Hi Youling,
>=20
> On Fri, 2022-09-02 at 18:08 +0800, Youling Tang wrote:
> > This tool is based on the arch/mips/boot/tools/relocs tool.
>=20
> I've dig some history of MIPS relocatable kernel
> (https://lwn.net/Articles/682020/):
>=20
> =C2=A0=C2=A0 * Kernel is compiled & statically linked as normal, with no =
position
> =C2=A0=C2=A0=C2=A0=C2=A0 independent code. MIPS before R6 only has limite=
d relative jump
> =C2=A0=C2=A0=C2=A0=C2=A0 instructions so the vast majority of jumps are a=
bsolute. To compile
> =C2=A0=C2=A0=C2=A0=C2=A0 the kernel position independent would introduce =
a highly undesireable
> =C2=A0=C2=A0=C2=A0=C2=A0 overhead. Relocating the static binary gives a s=
mall startup time
> =C2=A0=C2=A0=C2=A0=C2=A0 penalty but the kernel otherwise perforns normal=
ly.
>=20
> Unlike (pre-r6) MIPS, LoongArch has a complete support for PIC, and
> currently LoongArch toolchain always produces PIC (except, if -Wa,-mla-
> {local,global}-with-abs or la.abs macros are used explicitly).
>=20
> So would it be easier to review and correct the uses of "la.abs" in the
> code, and make the main kernel image a real PIE?=C2=A0 Then we can load i=
t
> everywhere w/o any need to do relocation at load time.

Arrgh, doing so will need to get rid of GOT (the GCC patch for this is
still under review) or we still need to relocate the GOT at least :(.


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