[PATCH] jump_label: align jump_entry table to at least 4-bytes

Jason Baron
2017-02-28T22:41:33Z

On 02/28/2017 03:15 PM, David Daney wrote:
> 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.
>
>
>

So before your module.lds script:

# powerpc64-linux-readelf -eW fs/nfsd/nfsd.o | grep jump

[31] __jump_table PROGBITS 0000000000000000 03edfe 0000f0
00 WA 0 0 1

# powerpc64-linux-readelf -eW fs/nfsd/nfsd.ko | grep jump

[32] __jump_table PROGBITS 0000000000000000 044046 0000f0
00 WA 0 0 1

With your patch:

# powerpc64-linux-readelf -eW fs/nfsd/nfsd.o | grep jump

[31] __jump_table PROGBITS 0000000000000000 03edfe 0000f0
00 WA 0 0 1

# powerpc64-linux-readelf -eW fs/nfsd/nfsd.ko | grep jump

[18] __jump_table PROGBITS 0000000000000000 03e358 0000f0
00 WA 0 0 8

I also checked all the other .ko files and they were properly aligned.
So I think this should hopefully work, and I like that its not a
per-arch fix.

Sachin, sorry to bother you again, but I'm hoping you can try David's
latest patch to scripts/module-common.lds, just to test in your setup.

Thanks,

-Jason