linux-kernel - Re: [PATCH v2 18/62] objtool: Fix x86 addend calculation

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Message-ID: <tvf7obye6afduyyefjrgicut2ehtyy4dkabxzxudtb55njsoba@4bhwzl3ftxeo>
Date: Wed, 4 Jun 2025 16:53:05 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>, 
	Joe Lawrence <joe.lawrence@...hat.com>, live-patching@...r.kernel.org, Song Liu <song@...nel.org>, 
	laokz <laokz@...mail.com>, Jiri Kosina <jikos@...nel.org>, 
	Marcos Paulo de Souza <mpdesouza@...e.com>, Weinan Liu <wnliu@...gle.com>, 
	Fazla Mehrab <a.mehrab@...edance.com>, Chen Zhongjin <chenzhongjin@...wei.com>, 
	Puranjay Mohan <puranjay@...nel.org>
Subject: Re: [PATCH v2 18/62] objtool: Fix x86 addend calculation

On Mon, May 26, 2025 at 12:23:15PM +0200, Peter Zijlstra wrote:
> On Fri, May 09, 2025 at 01:16:42PM -0700, Josh Poimboeuf wrote:
> > On x86, arch_dest_reloc_offset() hardcodes the addend adjustment to
> > four, but the actual adjustment depends on the relocation type.  Fix
> > that.
> 
> > +s64 arch_insn_adjusted_addend(struct instruction *insn, struct reloc *reloc)
> >  {
> > -	return addend + 4;
> > +	s64 addend = reloc_addend(reloc);
> > +
> > +	switch (reloc_type(reloc)) {
> > +	case R_X86_64_PC32:
> > +	case R_X86_64_PLT32:
> > +		addend += insn->offset + insn->len - reloc_offset(reloc);
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +
> > +	return addend;
> >  }
> 
> Should this not be something like:
> 
> s64 arch_insn_adjusted_addend(struct instruction *insn, struct reloc *reloc)
> {
> 	s64 addend = reloc_addend(reloc);
> 
> 	if (arch_pc_relative_reloc(reloc))
> 		addend += insn->offset + insn->len - reloc_offset(reloc);
> 
> 	return addend;
> }
> 
> instead?
> 
> AFAIU arch_pc_relative_reloc() is the exact same set of relocations.

Yeah that's better, thanks.

-- 
Josh