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 09:52:24 +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

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/

Huacai

>
> 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.
>
> Note that __jump_table is not generated by the compiler so
> -fno-jump-table is completely irrelevant for this issue.
>
> Fixes: cb8a2ef0848c ("LoongArch: Add ORC stack unwinder support")
> Closes: https://lore.kernel.org/loongarch/Zl5m1ZlVmGKitAof@yujie-X299/
> Closes: https://lore.kernel.org/loongarch/ZlY1gDDPi_mNrwJ1@slm.duckdns.org/
> Closes: https://lore.kernel.org/loongarch/1717478006.038663-1-hengqi@linux.alibaba.com/
> Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=816029e06768
> Link: https://github.com/llvm/llvm-project/commit/42cb3c6346fc
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> ---
>  arch/loongarch/Kconfig       | 5 ++++-
>  arch/loongarch/Kconfig.debug | 1 +
>  2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index e38139c576ee..e461a6c59f15 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -143,7 +143,7 @@ config LOONGARCH
>         select HAVE_LIVEPATCH
>         select HAVE_MOD_ARCH_SPECIFIC
>         select HAVE_NMI
> -       select HAVE_OBJTOOL if AS_HAS_EXPLICIT_RELOCS
> +       select HAVE_OBJTOOL if AS_HAS_EXPLICIT_RELOCS && AS_HAS_THIN_ADD_SUB
>         select HAVE_PCI
>         select HAVE_PERF_EVENTS
>         select HAVE_PERF_REGS
> @@ -273,6 +273,9 @@ config AS_HAS_LBT_EXTENSION
>  config AS_HAS_LVZ_EXTENSION
>         def_bool $(as-instr,hvcl 0)
>
> +config AS_HAS_THIN_ADD_SUB
> +       def_bool $(cc-option,-Wa$(comma)-mthin-add-sub) || CC_IS_CLANG
> +
>  menu "Kernel type and options"
>
>  source "kernel/Kconfig.hz"
> diff --git a/arch/loongarch/Kconfig.debug b/arch/loongarch/Kconfig.debug
> index 98d60630c3d4..8b2ce5b5d43e 100644
> --- a/arch/loongarch/Kconfig.debug
> +++ b/arch/loongarch/Kconfig.debug
> @@ -28,6 +28,7 @@ config UNWINDER_PROLOGUE
>
>  config UNWINDER_ORC
>         bool "ORC unwinder"
> +       depends on HAVE_OBJTOOL
>         select OBJTOOL
>         help
>           This option enables the ORC (Oops Rewind Capability) unwinder for
> --
> 2.45.2
>