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

[Xi Ruoyao <xry111@xry111.site>]

On Thu, 2024-06-06 at 10:10 +0800, Jinyang He wrote:
> What I just confused is that there is no ".cfi_*"
> in the eplogue by clang, which may cause wrong backtrace if gdb set
> 
> breakpoint there and backtrace. (But this is out of this topic.)

I don't think it'll cause wrong backtrace.  The real assemble code has
restored the registers and missing .cfi_restore will just make unwinder
restore them again.  There are redundant works but not breakages.

For objtool the main difference seems a thing explained in
https://maskray.me/blog/2020-11-08-stack-unwinding by Fangrui:

   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.

So perhaps we just need to code a constant named "PREV_BP_OFFSET" or
something in arch/ and use it in update_cfi_state() instead of fully re-
implement the entire function?
-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University