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

[David Daney <ddaney@caviumnetworks.com>]

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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.






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>From 89d4deafbc920351b93afb1ac4b4124995e1f19d Mon Sep 17 00:00:00 2001
From: David Daney <david.daney@cavium.com>
Date: Tue, 28 Feb 2017 12:10:02 -0800
Subject: [PATCH] module: set __jump_table alignment to 8

For powerpc the __jump_table section in modules is not aligned, this
causes an OOPS when loading a module containing a __jump_table.

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>
---
 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