linux-kernel - Re: [PATCH] module: set __jump

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Date:   Thu, 02 Mar 2017 21:47:07 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     David Daney <david.daney@...ium.com>,
        Jason Baron <jbaron@...mai.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Cc:     linux-mips@...ux-mips.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Russell King <linux@...linux.org.uk>,
        Rabin Vincent <rabin@....in>,
        Paul Mackerras <paulus@...ba.org>,
        Anton Blanchard <anton@...ba.org>,
        Ingo Molnar <mingo@...nel.org>, Zhigang Lu <zlu@...hip.com>,
        David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] module: set __jump_table alignment to 8

David Daney <david.daney@...ium.com> writes:

> For powerpc the __jump_table section in modules is not aligned, this
> causes a WARN_ON() splat when loading a module containing a __jump_table.

Thanks for doing the patch.

If it helps:

Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)

> Strict alignment became necessary with commit 3821fd35b58d
> ("jump_label: Reduce the size of struct static_key"), currently in
> linux-next, which uses the two least significant bits of pointers to
> __jump_table elements.

It would obviously be nice if this could go in before the commit that
exposes the breakage, but I guess that's problematic because Steve
doesn't want to rebase the tracing tree.

Steve I think you've already sent your pull request for this cycle? So I
guess if this can go in your first batch of fixes?

Or we could just send it directly to Linus?

cheers

> Fix by forcing __jump_table to 8, which is the same alignment used for
> this section in the kernel proper.
>
> Signed-off-by: David Daney <david.daney@...ium.com>
> Tested-by: Sachin Sant <sachinp@...ux.vnet.ibm.com>
> ---
>  scripts/module-common.lds | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/scripts/module-common.lds b/scripts/module-common.lds
> index 73a2c7d..53234e8 100644
> --- a/scripts/module-common.lds
> +++ b/scripts/module-common.lds
> @@ -19,4 +19,6 @@ SECTIONS {
>  
>  	. = ALIGN(8);
>  	.init_array		0 : { *(SORT(.init_array.*)) *(.init_array) }
> +
> +	__jump_table		0 : ALIGN(8) { KEEP(*(__jump_table)) }
>  }
> -- 
> 2.9.3