linux-kernel - Re: [PATCH v5 03/10] objtool: Handle PC relative relocation type

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Message-ID: <20241209203544.axetpzva7vg3hsc5@jpoimboe>
Date: Mon, 9 Dec 2024 12:35:44 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 03/10] objtool: Handle PC relative relocation type

On Sat, Dec 07, 2024 at 09:59:08AM +0800, Tiezhu Yang wrote:
> +unsigned long arch_adjust_offset(struct reloc *reloc, struct reloc *table)
> +{
> +	switch (reloc_type(reloc)) {
> +	case R_LARCH_32_PCREL:
> +	case R_LARCH_64_PCREL:
> +		if (reloc->sym->type == STT_SECTION)
> +			return reloc->sym->offset + reloc_addend(reloc) -
> +			       (reloc_offset(reloc) - reloc_offset(table));

How does this even work?  i.e., why does the reloc offset (basically the
jump table index) have anything to do with calculating the location of
the instruction it's referencing?

> +		else
> +			return reloc->sym->offset;

This also seems odd.  Why is the addend being ignored?  Shouldn't it
point to the instruction's offset?

-- 
Josh