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

[Huacai Chen]

Hi, Ruoyao and Jinyang,

On Fri, Jun 7, 2024 at 4:29 PM Xi Ruoyao <xry111@xxxxxxxxxxx> 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 frame
> > >      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@xxxxxxxxxxx>
> School of Aerospace Science and Technology, Xidian University
>