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

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Date:   Tue, 06 Sep 2022 13:17:45 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Youling Tang <tangyouling@...ngson.cn>,
        Jinyang He <hejinyang@...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 Tue, 2022-09-06 at 10:16 +0800, Youling Tang wrote:

> Switch to relative exception tables:
> 
> https://github.com/tangyouling/linux/commit/6525b8da
> https://github.com/tangyouling/linux/commit/b6ac0827
> 
> Will switch to the relative exception tables after applying the above
> two patches. So there is no need to relocate the exception table
> (remove relocate_exception_table).
> 
> Now we can remove the relocation of la.abs , got and ex_table, but
> still need to relocate LARCH_64. Is there anything else that needs to
> be modified to eliminate this relocation?

You may see the RISC-V patch as a reference:

https://lore.kernel.org/all/20211009171259.2515351-2-alexandre.ghiti@canonical.com/

Basically, make the linker to generate R_*_RELATIVE instead of R_*_64
for pointers.  And, perform R_*_RELATIVE relocation loading the kernel.

Something problematic IMO: RISC-V uses "-shared" to trick the linker to
generate R_*_RELATIVE but I consider it ugly (if the kernel is a shared
library, my grandma will be a wagon!)  I prefer "-pie -static", but our
Glibc does not have static-pie support for now.  It won't really affect
the kernel (we are -nostdlib), but we cannot learn how to handle
R_*_RELATIVE in static pie from Glibc then.

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