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From: Huacai Chen <chenhuacai@kernel.org>
Date: Sat, 15 Jun 2024 16:45:26 +0800
Message-ID: <CAAhV-H5Wz=U4kbX+tXt1qoCr6RaEDkzZXV7B=tgU_8o+X-NtVQ@mail.gmail.com>
Subject: Re: [PATCH] loongarch: Only select HAVE_OBJTOOL and allow ORC
 unwinder if the inline assembler supports R_LARCH_{32,64}_PCREL
To: Xi Ruoyao <xry111@xry111.site>
Cc: Jinyang He <hejinyang@loongson.cn>, Nathan Chancellor <nathan@kernel.org>, 
	Peter Zijlstra <peterz@infradead.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>, 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>
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Hi, Ruoyao and Jinyang,

On Fri, Jun 7, 2024 at 4:29=E2=80=AFPM Xi Ruoyao <xry111@xry111.site> wrote=
:
>
> On Fri, 2024-06-07 at 15:14 +0800, Jinyang He wrote:
> > >      Note: on RISC-V and LoongArch, the stack slot for the previous f=
rame
> > >      pointer is stored at fp[-2] instead of fp[0]. See [Consider
> > >      standardising which stack slot fp points
> > >      to](https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/=
18)
> > >      for the RISC-V discussion.
> >
> > In most cases the $fp is saved at cfa-16. But for va args, something
> > becomes different at LoongArch (I do not know the case of riscv), the
> > $fp isn't saved at cfa-16. (e.g. printk?)
>
> Oops indeed.  Even with a very simple case:
>
> int sum(int a, int b) {
>         return a + b;
> }
>
> with -fno-omit-frame-pointer we get:
>
> sum:
>         addi.d  $r3,$r3,-16
>         st.d    $r22,$r3,8
>         addi.d  $r22,$r3,16
>         ld.d    $r22,$r3,8
>         add.w   $r4,$r4,$r5
>         addi.d  $r3,$r3,16
>         jr      $r1
>
> So for leaf functions (where we don't save $ra) $fp is saved at cfa-8.
>
> > I feel that the update_cfi_state should be arch specific. I believe
> > that some logic can be reused, but each arch may have its own logic.
>
> I agree it now.
What is the conclusion about the clang part now? And for the original
-mno-thin-add-sub problem, do you have some way to fix it in the root?
I think we needn't rush, there are some weeks before 6.10 released.

Huacai

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