linux-kernel - Re: [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC unwinder if the inline assembler supports R_LARCH_{32,64}

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Date: Wed, 05 Jun 2024 12:38:03 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>, Tiezhu Yang <yangtiezhu@...ngson.cn>, 
 Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers
 <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, Justin Stitt
 <justinstitt@...gle.com>, Youling Tang <tangyouling@...inos.cn>, Jinyang He
 <hejinyang@...ngson.cn>,  loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
 mengqinggang@...ngson.cn, cailulu@...ngson.cn, wanglei@...ngson.cn, 
 luweining@...ngson.cn, Yujie Liu <yujie.liu@...el.com>, Heng Qi
 <hengqi@...ux.alibaba.com>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC
 unwinder if the inline assembler supports R_LARCH_{32,64}_PCREL

On Wed, 2024-06-05 at 09:52 +0800, Huacai Chen wrote:
> Hi, Ruoyao,
> 
> On Tue, Jun 4, 2024 at 11:08 PM Xi Ruoyao <xry111@...111.site> wrote:
> > 
> > GAS <= 2.41 does not support generating R_LARCH_{32,64}_PCREL for
> > "label - ." and it generates R_LARCH_{ADD,SUB}{32,64} pairs instead.
> > objtool cannot handle R_LARCH_{ADD,SUB}{32,64} pair in __jump_table
> > (static key implementation) and etc. so it will produce some warnings.
> > This is causing the kernel CI systems to complain everywhere.
> > 
> > For GAS we can check if -mthin-add-sub option is available to know if
> > R_LARCH_{32,64}_PCREL are supported.
> I think we should give a chance to toolchains without the
> -mthin-add-sub option, so I hope Tiezhu can resubmit this patch to
> solve this problem.
> https://lore.kernel.org/loongarch/1690272910-11869-6-git-send-email-yangtiezhu@loongson.cn/

It only handles .discard.{un,}reachable but not __jump_table. 
__jump_table is our main issue here.  And I don't see a quick way to
make -mno-thin-add-sub work for __jump_table because we really need to
resolve the relocation for __jump_table instead of simply skipping it.

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