linux-kernel - Re: [PATCH v12 01/12] livepatch: Change void *new_func -> unsigned long new_addr in struct klp

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Date:   Fri, 31 Aug 2018 10:37:36 +0200 (CEST)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Petr Mladek <pmladek@...e.com>
cc:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jason Baron <jbaron@...mai.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 01/12] livepatch: Change void *new_func -> unsigned
 long new_addr in struct klp_func

On Tue, 28 Aug 2018, Petr Mladek wrote:

> The address of the to be patched function and new function is stored
> in struct klp_func as:
> 
> 	void *new_func;
> 	unsigned long old_addr;
> 
> The different naming scheme and type is derived from the way how
> the addresses are set. @old_addr is assigned at runtime using
> kallsyms-based search. @new_func is statically initialized,
> for example:
> 
>   static struct klp_func funcs[] = {
> 	{
> 		.old_name = "cmdline_proc_show",
> 		.new_func = livepatch_cmdline_proc_show,
> 	}, { }
>   };
> 
> This patch changes void *new_func -> unsigned long new_addr. It removes
> some confusion when these address are later used in the code. It is
> motivated by a followup patch that adds special NOP struct klp_func
> where we want to assign func->new_func = func->old_addr respectively
> func->new_addr = func->old_addr.
> 
> This patch does not modify the existing behavior.
> 
> IMPORTANT: This patch modifies ABI. The patches will need to use,
> for example:
> 
>   static struct klp_func funcs[] = {
> 	{
> 		.old_name = "cmdline_proc_show",
> 		.new_addr = (unsigned long)livepatch_cmdline_proc_show,
> 	}, { }
>   };
> 
> Suggested-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Signed-off-by: Petr Mladek <pmladek@...e.com>

I'm not convinced the patch makes things any better. The next patch 
slightly improves it, but still. Is new_func really such a problem?

Thanks,
Miroslav