Re: [linux-next:master 11080/11173] drivers/media/common/saa7146/saa7146_hlp.c:648:5: warning: stack frame size of 1072 bytes in function 'saa7146_enable_overlay'

[Nick Desaulniers <ndesaulniers@google.com>]

On Mon, Sep 28, 2020 at 12:03 AM 'Marco Elver' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> On Sun, 27 Sep 2020 at 22:14, kernel test robot <lkp@intel.com> wrote:
> >
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head:   20dc779fdefc40bf7dd9736cea01704f29228fae
> > commit: 2ce416ba162877d5cf267ac35548ea45eba84150 [11080/11173] ubsan: introduce CONFIG_UBSAN_LOCAL_BOUNDS for Clang
> > config: powerpc-randconfig-r004-20200927 (attached as .config)

^ randconfig

> > compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 6d374cf78c8a80a0bbfc7ce9bc80b3f183f44c80)
> > reproduce (this is a W=1 build):
> >         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> >         chmod +x ~/bin/make.cross
> >         # install powerpc cross compiling tool for clang build
> >         # apt-get install binutils-powerpc-linux-gnu
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=2ce416ba162877d5cf267ac35548ea45eba84150
> >         git remote add linux-next https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> >         git fetch --no-tags linux-next master
> >         git checkout 2ce416ba162877d5cf267ac35548ea45eba84150
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=powerpc
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@intel.com>
> >
> > All warnings (new ones prefixed by >>):
> >
> > >> drivers/media/common/saa7146/saa7146_hlp.c:648:5: warning: stack frame size of 1072 bytes in function 'saa7146_enable_overlay' [-Wframe-larger-than=]
> >    int saa7146_enable_overlay(struct saa7146_fh *fh)
> >        ^
> >    1 warning generated.
>
> This warning must have existed before, because the UBSAN patch didn't
> add any features, it just guarded them with extra Kconfig options.

Likely.

>
> Also, this is with Clang 12, which is very much in development and
> quite unstable.

I wrote a tool that can help debug these:
https://github.com/ClangBuiltLinux/frame-larger-than

The compiler is quite unhelpful in the warning; but recompiling with
debug info gives you info about stack slots and the size of those
types.  This is a randconfig, so always weird things get pulled in.
Sometimes these are large stack allocations that should be heap
allocated; sometimes it's KASAN enabled via randconfig.  I noticed
that KASAN+clang has pretty poor stack slot reuse, which triggers
these often: https://github.com/ClangBuiltLinux/linux/issues/39  I
didn't check this config to see if KASAN was set or not, but I
wouldn't chalk it up to "clang 12 being unstable."

>
> > vim +/saa7146_enable_overlay +648 drivers/media/common/saa7146/saa7146_hlp.c
> >
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  647
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16 @648  int saa7146_enable_overlay(struct saa7146_fh *fh)
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  649  {
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  650        struct saa7146_dev *dev = fh->dev;
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  651        struct saa7146_vv *vv = dev->vv_data;
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  652
> > 5da545ad08a3c6 drivers/media/common/saa7146_hlp.c Hans Verkuil   2012-05-01  653        saa7146_set_window(dev, vv->ov.win.w.width, vv->ov.win.w.height, vv->ov.win.field);
> > 5da545ad08a3c6 drivers/media/common/saa7146_hlp.c Hans Verkuil   2012-05-01  654        saa7146_set_position(dev, vv->ov.win.w.left, vv->ov.win.w.top, vv->ov.win.w.height, vv->ov.win.field, vv->ov_fmt->pixelformat);
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  655        saa7146_set_output_format(dev, vv->ov_fmt->trans);
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  656        saa7146_set_clipping_rect(fh);
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  657
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  658        /* enable video dma1 */
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  659        saa7146_write(dev, MC1, (MASK_06 | MASK_22));
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  660        return 0;
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  661  }
> > ^1da177e4c3f41 drivers/media/common/saa7146_hlp.c Linus Torvalds 2005-04-16  662
> >
> > :::::: The code at line 648 was first introduced by commit
> > :::::: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Linux-2.6.12-rc2
> >
> > :::::: TO: Linus Torvalds <torvalds@ppc970.osdl.org>
> > :::::: CC: Linus Torvalds <torvalds@ppc970.osdl.org>
> >
> > ---
> > 0-DAY CI Kernel Test Service, Intel Corporation
> > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>
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-- 
Thanks,
~Nick Desaulniers