linux-kernel - Re: [RFC 04/13] objtool: Print symbol during disassembly

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Message-ID: <hnumdfr5kr2lxtkusiusfvjcz3j67jq5y43taadjuxn6xvmupp@c54u654r7ta3>
Date: Tue, 10 Jun 2025 14:55:39 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Alexandre Chartre <alexandre.chartre@...cle.com>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, peterz@...radead.org
Subject: Re: [RFC 04/13] objtool: Print symbol during disassembly

On Fri, Jun 06, 2025 at 05:34:31PM +0200, Alexandre Chartre wrote:
> +static void disas_print_address(bfd_vma addr, struct disassemble_info *dinfo)
> +{
> +	struct disas_context *dctx = dinfo->application_data;
> +	struct instruction *insn = dctx->insn;
> +	struct objtool_file *file = dctx->file;
> +	struct symbol *call_dest, *sym;
> +	struct instruction *jump_dest;
> +	struct section *sec;
> +	struct reloc *reloc;
> +	bool is_reloc;
> +	s64 offset;
> +
> +	/*
> +	 * If the instruction is a call/jump and it references a
> +	 * destination then this is likely the address we are looking
> +	 * up. So check it first.
> +	 */
> +	jump_dest = insn->jump_dest;
> +	if (jump_dest && jump_dest->offset == addr) {
> +		DINFO_FPRINTF(dinfo, "%lx <%s+0x%lx>", addr,
> +			      jump_dest->sym->name,
> +			      jump_dest->offset - jump_dest->sym->offset);
> +		return;
> +	}

IIRC, there may be a few cases where an instruction's 'sym' field can be
NULL, might want to check for !jump_dest->sym here.

> +	/*
> +	 * If this is a relocation, check if we have relocation information
> +	 * for this instruction.
> +	 */
> +	reloc = find_reloc_by_dest_range(file->elf, insn->sec,
> +					 insn->offset, insn->len);
> +	if (!reloc) {
> +		DINFO_FPRINTF(dinfo, "0x%lx", addr);
> +		return;
> +	}
> +
> +	if (reloc_type(reloc) == R_X86_64_PC32 ||
> +	    reloc_type(reloc) == R_X86_64_PLT32)

Can use arch_pc_relative_reloc() here.

> +		offset = arch_dest_reloc_offset(reloc_addend(reloc));
> +	else
> +		offset = reloc_addend(reloc);
> +
> +	/*
> +	 * If the relocation symbol is a section name (for example ".bss")
> +	 * then we try to further resolve the name.
> +	 */

This can be checked with reloc->sym->type == STT_SECTION.

> +	sec = find_section_by_name(file->elf, reloc->sym->name);
> +	if (sec) {
> +		sym = find_symbol_containing(sec, offset);
> +		if (sym) {
> +			if (sym->offset == offset)
> +				DINFO_FPRINTF(dinfo, "%s+0x%lx = %s",
> +					     reloc->sym->name, offset, sym->name);
> +			else
> +				DINFO_FPRINTF(dinfo, "%s+0x%lx = %s+0x%lx",
> +					      reloc->sym->name, offset,
> +					      sym->name, offset - sym->offset);
> +			return;
> +		}
> +	}
> +
> +	if (offset)
> +		DINFO_FPRINTF(dinfo, "%s+0x%lx", reloc->sym->name, offset);
> +	else
> +		DINFO_FPRINTF(dinfo, "%s", reloc->sym->name);

We have offstr() which does similar things.  You might be able to get
away with replacing the above hunk with something like:

	DINFO_FPRINTF(dinfo, "%s", offstr(reloc->sym->sec, sym->offset + offset));

-- 
Josh