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Re: [PATCH] module: set __jump_table alignment to 8

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  Re: [PATCH] module: set __jump_table alignment to 8 Michael Ellerman <mpe@ellerman.id.au> - 2017-03-02 12:00 +0100
    Re: [PATCH] module: set __jump_table alignment to 8 Michael Ellerman <mpe@ellerman.id.au> - 2017-03-02 16:00 +0100
      Re: [PATCH] module: set __jump_table alignment to 8 Steven Rostedt <rostedt@goodmis.org> - 2017-03-02 18:50 +0100
        Re: [PATCH] module: set __jump_table alignment to 8 Michael Ellerman <mpe@ellerman.id.au> - 2017-03-03 04:50 +0100

#1590998 — Re: [PATCH] module: set __jump_table alignment to 8

David Daney <david.daney@cavium.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@ellerman.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@cavium.com>
> Tested-by: Sachin Sant <sachinp@linux.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

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#1591166

Michael Ellerman <mpe@ellerman.id.au> writes:
> David Daney <david.daney@cavium.com> writes:
>> 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?

Ugh. Was looking at the wrong tree - Linus has already merged the commit
in question, so the above is all moot.

cheers

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#1591341

On Thu, 02 Mar 2017 22:18:30 +1100
Michael Ellerman <mpe@ellerman.id.au> wrote:

> Michael Ellerman <mpe@ellerman.id.au> writes:
> > David Daney <david.daney@cavium.com> writes:  
> >> 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?  
> 
> Ugh. Was looking at the wrong tree - Linus has already merged the commit
> in question, so the above is all moot.

No problem. I've got some other "fixes" to push to Linus. That's what
the -rc releases are for. To fix up breakage from the merge window ;-)

I'll pull this into my tree.

Thanks!

-- Steve

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#1591655

Steven Rostedt <rostedt@goodmis.org> writes:
> On Thu, 02 Mar 2017 22:18:30 +1100
> Michael Ellerman <mpe@ellerman.id.au> wrote:
>> Michael Ellerman <mpe@ellerman.id.au> writes:
>> > David Daney <david.daney@cavium.com> writes:  
>> >> 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?  
>> 
>> Ugh. Was looking at the wrong tree - Linus has already merged the commit
>> in question, so the above is all moot.
>
> No problem. I've got some other "fixes" to push to Linus. That's what
> the -rc releases are for. To fix up breakage from the merge window ;-)

Yep, no drama.

> I'll pull this into my tree.

Thanks.

cheers

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