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

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Message-ID: <20250526102315.GK24938@noisy.programming.kicks-ass.net>
Date: Mon, 26 May 2025 12:23:15 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.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 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.