linux-kernel - Re: drivers/video/backlight/ltv350qv.c:192:12: warning: stack frame size of 13472 bytes in function 'ltv350qv

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Date:   Wed, 28 Oct 2020 15:46:13 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     kernel test robot <lkp@...el.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        kbuild-all@...ts.01.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: drivers/video/backlight/ltv350qv.c:192:12: warning: stack frame
 size of 13472 bytes in function 'ltv350qv_power'

On Sun, Oct 25, 2020 at 12:17:08PM -0700, Andrew Morton wrote:
> On Mon, 26 Oct 2020 02:15:37 +0800 kernel test robot <lkp@...el.com> wrote:
> 
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   d76913908102044f14381df865bb74df17a538cb
> > commit: cae9dc35ed9ff82a99754e51d57ff6c332e1f7e4 kasan: allow enabling stack tagging for tag-based mode
> > date:   3 months ago
> > config: arm64-randconfig-r005-20201026 (attached as .config)
> > compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project 1c8371692dfe8245bc6690ff1262dcced4649d21)
> > 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 arm64 cross compiling tool for clang build
> >         # apt-get install binutils-aarch64-linux-gnu
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cae9dc35ed9ff82a99754e51d57ff6c332e1f7e4
> >         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >         git fetch --no-tags linus master
> >         git checkout cae9dc35ed9ff82a99754e51d57ff6c332e1f7e4
> >         # save the attached .config to linux build tree
> >         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=arm64 
> > 
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@...el.com>
> > 
> > All warnings (new ones prefixed by >>):
> > 
> > >> drivers/video/backlight/ltv350qv.c:192:12: warning: stack frame size of 13472 bytes in function 'ltv350qv_power' [-Wframe-larger-than=]
> 
> That's a lot of stack.
> 
> >    static int ltv350qv_power(struct ltv350qv *lcd, int power)
> >               ^
> >    1 warning generated.
> > 
> > vim +/ltv350qv_power +192 drivers/video/backlight/ltv350qv.c
> 
> Odd - the code looks pretty normal.  It is possible that your compiler
> is (crazily) inlining ltv350qv_write_reg()?

Certainly could be.

Same config compiled with gcc-9 gives ltv350qv_write_reg() a stack usage
that is large but not crazy: 768 bytes and dropping to 480 bytes with
the sanitizers disabled. With the sanitizers enabled then even the 
cumulative stack usage of ltv350qv_power() through to ltv350qv_write_reg() is
still less than 1k.


Daniel.