linux-kernel - Re: [PATCH] nvdimm: constify device

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Date:   Tue, 24 Jan 2017 18:49:29 -0800
From:   Joe Perches <joe@...ches.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Bhumika Goyal <bhumirks@...il.com>,
        Julia Lawall <julia.lawall@...6.fr>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] nvdimm: constify device_type structures

On Tue, 2017-01-24 at 18:40 -0800, Dan Williams wrote:
> On Tue, Jan 24, 2017 at 6:37 PM, Joe Perches <joe@...ches.com> wrote:
> > On Wed, 2017-01-25 at 00:54 +0530, Bhumika Goyal wrote:
> > > Declare device_type structure as const as it is only stored in the
> > > type field of a device structure. This field is of type const, so add
> > > const to declaration of device_type structure.
> > > 
> > > File size before:
> > >   text           data     bss     dec     hex filename
> > >   19278          3199      16   22493    57dd nvdimm/namespace_devs.o
> > > 
> > > File size after:
> > >   text           data     bss     dec     hex filename
> > >   19929          3160      16   23105    5a41 nvdimm/namespace_devs.o
> > 
> > Fine, but are you sure about the sizes?
> > 
> > It seems odd the text went up 651 bytes
> > while the data went down just 39 bytes.
> > 
> 
> Right, the size data wasn't why I applied it. It was the general rule
> of "make function pointer data read-only whenever possible to
> eliminate a kernel attack vector".

Exactly the correct reason it's a fine patch and one
that should be applied.

> Bhumika, you might want to mention
> this as the motivating reason to apply the patch if you do more of
> these changes.

Regardless, the object sizes are still odd.

The config should be mentioned because actually,
the commonly compiles sizes reported are not correct.

with an x86-64 defconfig I get:

$ size drivers/nvdimm/namespace_devs.o*
   text	   data	    bss	    dec	    hex	filename
  14615	    519	     16	  15150	   3b2e	drivers/nvdimm/namespace_devs.o.new
  14439	    695	     16	  15150	   3b2e	drivers/nvdimm/namespace_devs.o.old