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

[Jason Baron]

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