Re: [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC unwinder if the inline assembler supports R_LARCH_{32,64}_PCREL

[Heng Qi]

On Tue,  4 Jun 2024 23:07:41 +0800, Xi Ruoyao <xry111@xxxxxxxxxxx> 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.
> 
> Note that __jump_table is not generated by the compiler so
> -fno-jump-table is completely irrelevant for this issue.
> 

Hi Xi Ruoyao,

I want to know does this patch fix the following warning:
https://lore.kernel.org/all/202406040645.6z95FW1f-lkp@xxxxxxxxx/ ?

Thanks.

> 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@xxxxxxxxxxxxxxx/
> Closes: https://lore.kernel.org/loongarch/1717478006.038663-1-hengqi@xxxxxxxxxxxxxxxxx/
> 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@xxxxxxxxxxx>
> ---
>  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
>