linux-kernel - Re: [PATCH 2/3 v7] livepatch: add sympos as disambiguator field to klp

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Date:	Wed, 18 Nov 2015 10:56:00 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Chris J Arges <chris.j.arges@...onical.com>
cc:	live-patching@...r.kernel.org, jpoimboe@...hat.com,
	sjenning@...hat.com, jikos@...nel.org, vojtech@...e.com,
	pmladek@...e.com, jeyu@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3 v7] livepatch: add sympos as disambiguator field to
 klp_reloc

On Mon, 16 Nov 2015, Chris J Arges wrote:

> @@ -281,29 +243,26 @@ static int klp_write_object_relocations(struct module *pmod,
>  		return -EINVAL;
>  
>  	for (reloc = obj->relocs; reloc->name; reloc++) {
> -		if (!klp_is_module(obj)) {
> -			ret = klp_verify_vmlinux_symbol(reloc->name,
> -							reloc->val);
> -			if (ret)
> -				return ret;
> -		} else {
> -			/* module, reloc->val needs to be discovered */
> -			if (reloc->external)
> -				ret = klp_find_external_symbol(pmod,
> -							       reloc->name,
> -							       &reloc->val);
> -			else
> -				ret = klp_find_object_symbol(obj->mod->name,
> -							     reloc->name,
> -							     0, &reloc->val);
> -			if (ret)
> -				return ret;
> +		if (reloc->sympos && (reloc->sympos != 1)) {
> +			pr_err("symbol '%s' is external and has sympos %lu\n",
> +			       reloc->name, reloc->sympos);
> +			return -EINVAL;
>  		}

Oh, this check should not be here, right? I think it needs to be under 'if 
(reloc->external) {'.

And

if (reloc->sympos && (reloc->sympos != 1)) {

can be written as

if (reloc->sympos > 1) {

Anyway, I am not sure if this is the right thing to do. I know Petr 
suggested it, but maybe it would be sufficient just to error out when 
reloc->sympos is specified for external symbols. Despite there is a valid 
value (== 1). Like it had been done before. Josh came up with the issue. 
So what is your opinion, Josh? It is a nitpick, but nevertheless.

Miroslav

> +		/* discover the address of the referenced symbol */
> +		if (reloc->external) {
> +			ret = klp_find_external_symbol(pmod, reloc->name, &val);
> +		} else
> +			ret = klp_find_object_symbol(obj->mod->name,
> +						     reloc->name,
> +						     reloc->sympos,
> +						     &val);
> +		if (ret)
> +			return ret;
>  		ret = klp_write_module_reloc(pmod, reloc->type, reloc->loc,
> -					     reloc->val + reloc->addend);
> +					     val + reloc->addend);
>  		if (ret) {
>  			pr_err("relocation failed for symbol '%s' at 0x%016lx (%d)\n",
> -			       reloc->name, reloc->val, ret);
> +			       reloc->name, val, ret);
>  			return ret;
>  		}
>  	}
> 

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