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Message-ID: <b55b8cb2c52f2c3701c83353586130b8dc237ee2.camel@xry111.site>
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: Nathan Chancellor <nathan@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>, WANG Xuerui <kernel@xen0n.name>, 
 Tiezhu Yang <yangtiezhu@loongson.cn>, 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 13:54:24 +0800
In-Reply-To: <20240605054328.GA279426@thelio-3990X>
References: <20240604150741.30252-1-xry111@xry111.site>
	 <20240605054328.GA279426@thelio-3990X>
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On Tue, 2024-06-04 at 22:43 -0700, Nathan Chancellor wrote:
> On Tue, Jun 04, 2024 at 11:07:41PM +0800, Xi Ruoyao wrote:
> > 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.
> >=20
> > For Clang, we require Clang >=3D 18 and Clang >=3D 17 already supports
> > R_LARCH_{32,64}_PCREL, so we can always assume Clang is fine for
> > objtool.
>=20
> For what it's worth, I have noticed some warnings with clang that I
> don't see with GCC but I only filed an issue on our GitHub and never
> followed up on the mailing list, so sorry about that.
>=20
> https://github.com/ClangBuiltLinux/linux/issues/2024
>=20
> Might be tangential to this patch though but I felt it was worth
> mentioning.

The warnings in GCC build is definitely the issue handled by this patch.
But the warnings in Clang build should be a different issue.  Can you
attach the kernel/events/core.o file from the Clang build for analysis?
I guess we need to disable more optimization...

I personally hate "pessimizing the code generation just for debugging"
with a passion so I never enabled objtool on LoongArch, thus I didn't
notice the issue.

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