linux-kernel - Re: [PATCH] jump_label: align jump

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Message-ID: <912fa97a-aa1d-c0e4-dc83-fc5c745db1c1@caviumnetworks.com>
Date:   Tue, 28 Feb 2017 12:15:10 -0800
From:   David Daney <ddaney@...iumnetworks.com>
To:     Jason Baron <jbaron@...mai.com>,
        David Daney <ddaney@...iumnetworks.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sachin Sant <sachinp@...ux.vnet.ibm.com>
Cc:     linux-mips@...ux-mips.org, Chris Metcalf <cmetcalf@...lanox.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rabin Vincent <rabin@....in>,
        Paul Mackerras <paulus@...ba.org>,
        Anton Blanchard <anton@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, Zhigang Lu <zlu@...hip.com>
Subject: Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes

On 02/28/2017 11:34 AM, Jason Baron wrote:
>
>
> On 02/28/2017 02:22 PM, David Daney wrote:
>> On 02/28/2017 11:05 AM, David Daney wrote:
>>> On 02/28/2017 10:39 AM, Jason Baron wrote:
>>>>
>> [...]
>>>>> I suspect that the alignment of the __jump_table section in the .ko
>>>>> files is not correct, and you are seeing some sort of problem due to
>>>>> that.
>>>>>
>>>>>
>>>>
>>>> Hi,
>>>>
>>>> Yes, if you look at the trace that Sachin sent the module being loaded
>>>> that does the WARN_ON() is nfsd.ko.
>>>>
>>>> That module from Sachin's trace has:
>>>>
>>>>   [31] __jump_table      PROGBITS        0000000000000000 03fd77 0000c0
>>>> 18 WAM  0   0  1
>>>
>>> The problem is then the section alignment (last column) for power.
>>>
>>> On mips with no patches applied, we get:
>>>
>>>   [17] __jump_table      PROGBITS        0000000000000000 00d2c0 000048
>>> 00  WA  0   0  8
>>>
>>> Look, proper alignment!
>>>
>>> The question I have is why do the power ".llong" and ".long" assembler
>>> directives not force section alignment?  Is there an alternative that
>>> could be used that would result in the proper alignment?  Would ".word"
>>> work?
>>>
>>> If not, then I would say patch only power with your balign thing. 8-byte
>>> alignment for 64-bit kernel, 4-byte alignment for 32-bit kernel
>>>
>>
>> I think the proper fix is either:
>>
>> A) Modify scripts/module-common.lds to force __jump_table alignment for
>> all architectures.
>>
>> B) Add arch/powerpc/kernel/module.lds to force __jump_table alignment
>> for powerpc only.
>>
>> David.
>>
>>
>
> Ok, I can try adding it to the linger script.
>
> FWIW, here is my before and after with the .balign thing for the nfsd.ko
> module on powperc (using a cross-compiler):
>
> before:
>
>   [31] __jump_table      PROGBITS        0000000000000000 03ee3e 0000f0
> 00  WA  0   0  1
>
> after:
>
>  [31] __jump_table      PROGBITS        0000000000000000 03ee40 0000f0
> 00  WA  0   0  4
>

Try the (lightly tested) attached.

If it works and Steven likes it, perhaps someone can merge it.

David.






View attachment "0001-module-set-__jump_table-alignment-to-8.patch" of type "text/x-patch" (917 bytes)