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

[David Daney]

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.