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, 5 Jun 2024 13:21:21 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Xi Ruoyao <xry111@...111.site>
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, Jun 5, 2024 at 12:38 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> 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.
 __jump_table is disabled now, so we can only solve  -mno-thin-add-sub
at present, and the next step is __jump_table.

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