Re: [PATCH][RFC] err.h: silence sparse warning: dereference of noderef expression

[Josh Triplett <josh@joshtriplett.org>]

On Fri, Jun 13, 2014 at 08:05:37AM -0400, Jeff Layton wrote:
> On Thu, 12 Jun 2014 18:06:25 +1000
> Vitaly Osipov <vitaly.osipov@gmail.com> wrote:
> 
> > Nothing shows up for me on x86_64, allmodconfig, linux-next from 10 of
> > June. My sparse has been compiled from sources.
> > 
> > $ make fs/locks.o C=2 CHECK="/home/vosipov/bin/sparse"
> >   CHK     include/config/kernel.release
> >   CHK     include/generated/uapi/linux/version.h
> >   CHK     include/generated/utsrelease.h
> >   CALL    scripts/checksyscalls.sh
> >   CHECK   scripts/mod/empty.c
> >   CHECK   fs/locks.c
> > 
> > $ sparse —version
> > v0.5.0
> > 
> > $ which sparse
> > /home/vosipov/bin/sparse
> > 
> > Regards,
> > Vitaly
> > 
> > 
> > On Wed, Jun 11, 2014 at 11:51 PM, Jeff Layton <jlayton@poochiereds.net> wrote:
> > > On Wed, 11 Jun 2014 16:11:46 +0300
> > > Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > >
> > >> On Wed, Jun 11, 2014 at 07:06:32AM -0400, Jeff Layton wrote:
> > >> > $ rpm -q sparse
> > >> > sparse-0.5.0-1.fc20.x86_64
> > >> >
> > >> > I see it all over the tree, but an easy example is fs/locks.c:
> > >> >
> > >> > $ make fs/locks.o C=1
> > >> > make[1]: Nothing to be done for `all'.
> > >> > make[1]: Nothing to be done for `relocs'.
> > >> >   CHK     include/config/kernel.release
> > >> >   CHK     include/generated/uapi/linux/version.h
> > >> >   CHK     include/generated/utsrelease.h
> > >> >   CALL    scripts/checksyscalls.sh
> > >> >   CHECK   fs/locks.c
> > >> > include/linux/err.h:35:16: warning: dereference of noderef expression
> > >> > include/linux/err.h:30:23: warning: dereference of noderef expression
> > >> > include/linux/err.h:35:16: warning: dereference of noderef expression
> > >> > include/linux/err.h:30:23: warning: dereference of noderef expression
> > >> >   CC      fs/locks.o
> > >> >
> > >> > It has two IS_ERR calls and two PTR_ERR calls, and each generates the
> > >> > warning.
> > >> >
> > >>
> > >> I downloaded the Fedora SRPM and built the binary but I still wasn't
> > >> able to reproduce the bug.
> > >>
> > >> dcarpenter@speke:~/progs/kernel/devel$ /tmp/sparse/sparse-0.5.0/sparse --version
> > >> 0.5.0
> > >> dcarpenter@speke:~/progs/kernel/devel$ make C=2 CHECK=/tmp/sparse/sparse-0.5.0/sparse fs/locks.o
> > >>   CHK     include/config/kernel.release
> > >>   CHK     include/generated/uapi/linux/version.h
> > >>   CHK     include/generated/utsrelease.h
> > >>   CALL    scripts/checksyscalls.sh
> > >> <stdin>:1226:2: warning: #warning syscall finit_module not implemented [-Wcpp]
> > >> <stdin>:1229:2: warning: #warning syscall sched_setattr not implemented [-Wcpp]
> > >> <stdin>:1232:2: warning: #warning syscall sched_getattr not implemented [-Wcpp]
> > >> <stdin>:1235:2: warning: #warning syscall renameat2 not implemented [-Wcpp]
> > >>   CHECK   scripts/mod/empty.c
> > >>   CHECK   fs/locks.c
> > >> dcarpenter@speke:~/progs/kernel/devel$
> > >>
> > >> I'm on today's linux-next.  I can't think of a kernel configuration
> > >> issue which would cause this...
> > >>
> > >> regards,
> > >> dan carpenter
> > >
> > > Could it be arch-specific then? What arch are you using? I'm on x86_64.
> > > I know that quite a few other people have mentioned seeing these
> > > warnings as well, so I'm pretty sure it's not just me.
> > >
> 
> Ha! It turns out that my hand-built sparse also works fine, so the
> problem seems to be in the Fedora package.
> 
> With a little trial-and-error, I figured out what's causing the
> problem, but I'm a little baffled as to why it's occurring. 
> 
> The Fedora SRPM builds the program with -fpic. When I remove that flag,
> this problem goes away. I'd appreciate any insight into why that would
> break things. I doubt PIC really makes much difference security-wise in
> sparse, so removing it shouldn't matter much, but I wonder if this
> indicates an underlying bug in sparse itself?

Wow, that's horrifying.  I wonder if it might indicate a miscompilation
by GCC.  Does the problem persist if you build with -fpic -g?  If so,
you could set a few breakpoints and try to determine at what point the
behavior of the two sparse binaries diverges.

- Josh Triplett
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