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: Tue, 4 Jun 2024 22:43:28 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Xi Ruoyao <xry111@...111.site>
Cc: Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
	Tiezhu Yang <yangtiezhu@...ngson.cn>,
	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 Tue, Jun 04, 2024 at 11:07:41PM +0800, Xi Ruoyao 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.
> 
> For Clang, we require Clang >= 18 and Clang >= 17 already supports
> R_LARCH_{32,64}_PCREL, so we can always assume Clang is fine for
> objtool.

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.

https://github.com/ClangBuiltLinux/linux/issues/2024

Might be tangential to this patch though but I felt it was worth
mentioning.

Cheers,
Nathan