linux-kernel - Re: [PATCHv3 5/7] parisc64: Add .opd based function descriptor dereference

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Message-ID: <20171004104016.GG20084@pathway.suse.cz>
Date:   Wed, 4 Oct 2017 12:40:16 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        James Bottomley <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 5/7] parisc64: Add .opd based function descriptor
 dereference

On Sat 2017-09-30 11:53:17, Sergey Senozhatsky wrote:
> We are moving towards separate kernel and module function descriptor
> dereference callbacks. This patch enables it for parisc64.
> 
> For pointers that belong to the kernel
> -  Added __start_opd and __end_opd pointers, to track the kernel
>    .opd section address range;
> 
> -  Added dereference_kernel_function_descriptor(). Now we
>    will dereference only function pointers that are within
>    [__start_opd, __end_opd];
> 
> For pointers that belong to a module
> -  Added dereference_module_function_descriptor() to handle module
>    function descriptor dereference. Now we will dereference only
>    pointers that are within [module->opd.start, module->opd.end].

> diff --git a/arch/parisc/kernel/module.c b/arch/parisc/kernel/module.c
> index f1a76935a314..28f89b3dcc11 100644
> --- a/arch/parisc/kernel/module.c
> +++ b/arch/parisc/kernel/module.c
> @@ -954,3 +955,19 @@ void module_arch_cleanup(struct module *mod)
>  {
>  	deregister_unwind_table(mod);
>  }
> +
> +#ifdef CONFIG_64BIT
> +unsigned long dereference_module_function_descriptor(struct module *mod,
> +						     unsigned long addr)
> +{
> +	unsigned long start_opd = (Elf64_Addr)mod->core_layout.base +
> +				   mod->arch.fdesc_offset;
> +	unsigned long end_opd = start_opd +
> +				mod->arch.fdesc_count * sizeof(Elf64_Fdesc);

I know that this is used in rather slow paths. But it still might
make sense to have these section borders pre-computed and
stored in struct mod_arch_specific. I mean to do similar
thing that we do on powerpc.

Well, we could do this in a followup patch if parisc people
wanted it.


> +	if (addr < start_opd || addr >= end_opd)
> +		return addr;
> +
> +	return dereference_function_descriptor(addr);
> +}
> +#endif

Otherwise the patch looks fine to me.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr