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Message-ID: <329dac82e09dfc75e77ae93ebbeacdec1dc9ff7f.camel@xry111.site>
Date: Fri, 07 Jun 2024 16:29:09 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Jinyang He <hejinyang@...ngson.cn>, Nathan Chancellor
<nathan@...nel.org>, Peter Zijlstra <peterz@...radead.org>
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>,
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 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.
--
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University
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