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Subject: Re: [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC
 unwinder if the inline assembler supports R_LARCH_{32,64}_PCREL
From: Xi Ruoyao <xry111@xry111.site>
To: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>, Tiezhu Yang <yangtiezhu@loongson.cn>, 
 Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers
 <ndesaulniers@google.com>, Bill Wendling <morbo@google.com>, Justin Stitt
 <justinstitt@google.com>, Youling Tang <tangyouling@kylinos.cn>, Jinyang He
 <hejinyang@loongson.cn>,  loongarch@lists.linux.dev,
 linux-kernel@vger.kernel.org, llvm@lists.linux.dev, 
 mengqinggang@loongson.cn, cailulu@loongson.cn, wanglei@loongson.cn, 
 luweining@loongson.cn, Yujie Liu <yujie.liu@intel.com>, Heng Qi
 <hengqi@linux.alibaba.com>, Tejun Heo <tj@kernel.org>
Date: Wed, 05 Jun 2024 12:38:03 +0800
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References: <20240604150741.30252-1-xry111@xry111.site>
	 <CAAhV-H7CF5wUSj5qfSs-+YTUrB2R9STO7LLu7LG2RpsYE719Og@mail.gmail.com>
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On Wed, 2024-06-05 at 09:52 +0800, Huacai Chen wrote:
> Hi, Ruoyao,
>=20
> On Tue, Jun 4, 2024 at 11:08=E2=80=AFPM Xi Ruoyao <xry111@xry111.site> wr=
ote:
> >=20
> > GAS <=3D 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.
> >=20
> > 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-yangt=
iezhu@loongson.cn/

It only handles .discard.{un,}reachable but not __jump_table.=20
__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.

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