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From: Michael Ellerman <mpe@ellerman.id.au>
To: Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, Scott Wood <oss@buserror.net>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 3/3] powerpc/mm: Implement CONFIG_DEBUG_RODATA on PPC32
In-Reply-To: <eabf767c896a023e5670adfa07398f1008756c13.1492596044.git.christophe.leroy@c-s.fr>
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Date: Thu, 20 Apr 2017 00:01:39 +1000
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Christophe Leroy <christophe.leroy@c-s.fr> writes:

> diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
> index 32509de6ce4c..4af81fb23653 100644
> --- a/arch/powerpc/kernel/ftrace.c
> +++ b/arch/powerpc/kernel/ftrace.c
> @@ -526,7 +526,9 @@ void ftrace_replace_code(int enable)
>   */
>  void arch_ftrace_update_code(int command)
>  {
> +	set_kernel_text_rw();
>  	ftrace_modify_all_code(command);
> +	set_kernel_text_ro();
>  }
  
I'm not sure that's the right place for that.

If you look at other arches they hook into ftrace_modify_code(), where
you have the address that's being modified.

cheers