linux-kernel - Re: [PATCH 1/3] LoongArch: tools: Add relocs tool support

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Message-ID: <4df8a26c49a35c1fce36d80c370f738fa71a2bef.camel@xry111.site>
Date:   Fri, 02 Sep 2022 19:27:28 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Youling Tang <tangyouling@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
        Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH 1/3] LoongArch: tools: Add relocs tool support

On Fri, 2022-09-02 at 19:10 +0800, Xi Ruoyao wrote:
> Hi Youling,
> 
> On Fri, 2022-09-02 at 18:08 +0800, Youling Tang wrote:
> > This tool is based on the arch/mips/boot/tools/relocs tool.
> 
> I've dig some history of MIPS relocatable kernel
> (https://lwn.net/Articles/682020/):
> 
>    * Kernel is compiled & statically linked as normal, with no position
>      independent code. MIPS before R6 only has limited relative jump
>      instructions so the vast majority of jumps are absolute. To compile
>      the kernel position independent would introduce a highly undesireable
>      overhead. Relocating the static binary gives a small startup time
>      penalty but the kernel otherwise perforns normally.
> 
> 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).
> 
> 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?  Then we can load it
> 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 :(.


-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University