linux-kernel - Re: [PATCH v1 5/6] objtool: Add skipped member in struct reloc

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Date:   Wed, 09 Aug 2023 19:58:20 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Peter Zijlstra <peterz@...radead.org>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v1 5/6] objtool: Add skipped member in struct reloc

On Wed, 2023-08-09 at 19:51 +0800, Xi Ruoyao wrote:
> On Thu, 2023-08-03 at 14:11 +0200, Peter Zijlstra wrote:
> > On Thu, Aug 03, 2023 at 07:36:24PM +0800, Tiezhu Yang wrote:
> > 
> > > >                         ".long " __stringify_label(c) "b - .\n\t"          \
> > 
> > > I discussed offline with the engineers who are familiar with gnu
> > > assembler of LoongArch, maybe it can modify the gnu assembler
> > > to use R_LARCH_32_PCREL to replace a pair of R_LARCH_ADD32 and
> > > R_LARCH_SUB32, then I will test it again and drop this change if
> > > possible.
> 
> Hmm, but I don't like the idea to disallow users having GAS <= 2.41 from
> using ORC unwinder.
> 
> Can we emit the R_LARCH_32_PCREL reloc with an explicit .reloc
> directive?

Answering myself: "maybe", I've written a simple PoC:

$ cat t.s
.global main
main:
  la.pcrel $t0, f
  ld.w     $t1, $t0, 0
  ldx.d    $a0, $t1, $t0
  jr       $ra

t:
  .dword   42
  .zero    64

f:
  .reloc   f, R_LARCH_32_PCREL, t
  .word    0
$ ./a.out
$ echo $?
42
-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University