Re: [linux-next:master 3357/8413] drivers/scsi/FlashPoint.c:1712:12: warning: stack frame size (1056) exceeds limit (1024) in 'FlashPoint_HandleInterrupt'

[Kees Cook <keescook@chromium.org>]

On Sat, Jun 10, 2023 at 12:58:23AM +0800, kernel test robot wrote:
> First bad commit (maybe != root cause):
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   53ab6975c12d1ad86c599a8927e8c698b144d669
> commit: df8fc4e934c12b906d08050d7779f292b9c5c6b5 [3357/8413] kbuild: Enable -fstrict-flex-arrays=3
> config: powerpc-allmodconfig (https://download.01.org/0day-ci/archive/20230610/202306100035.VTusNhm4-lkp@intel.com/config)
> compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)
> reproduce (this is a W=1 build):
>         mkdir -p ~/bin
>         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=df8fc4e934c12b906d08050d7779f292b9c5c6b5
>         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 df8fc4e934c12b906d08050d7779f292b9c5c6b5
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash drivers/
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202306100035.VTusNhm4-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
>    In file included from drivers/scsi/BusLogic.c:51:
> >> drivers/scsi/FlashPoint.c:1712:12: warning: stack frame size (1056) exceeds limit (1024) in 'FlashPoint_HandleInterrupt' [-Wframe-larger-than]
>     1712 | static int FlashPoint_HandleInterrupt(void *pcard)
>          |            ^
>    1 warning generated.

I wasn't able to generate the warning with my Clang, but it sure is
close! Building with KCFLAGS=-Rpass-analysis=stack-frame-layout I see:


In file included from ../drivers/scsi/BusLogic.c:51:
../drivers/scsi/FlashPoint.c:1713:1: remark:
Function: FlashPoint_HandleInterrupt
Offset: [SP-4], Type: Protector, Align: 4, Size: 4
Offset: [SP-8], Type: Spill, Align: 8, Size: 4
Offset: [SP-12], Type: Spill, Align: 4, Size: 4
Offset: [SP-16], Type: Spill, Align: 16, Size: 4
Offset: [SP-20], Type: Spill, Align: 4, Size: 4
Offset: [SP-24], Type: Spill, Align: 8, Size: 4
Offset: [SP-28], Type: Spill, Align: 4, Size: 4
Offset: [SP-32], Type: Spill, Align: 16, Size: 4
Offset: [SP-36], Type: Spill, Align: 4, Size: 4
Offset: [SP-40], Type: Spill, Align: 8, Size: 4
Offset: [SP-44], Type: Spill, Align: 4, Size: 4
Offset: [SP-48], Type: Spill, Align: 16, Size: 4
Offset: [SP-52], Type: Spill, Align: 4, Size: 4
Offset: [SP-56], Type: Spill, Align: 8, Size: 4
Offset: [SP-60], Type: Spill, Align: 4, Size: 4
Offset: [SP-64], Type: Spill, Align: 16, Size: 4
Offset: [SP-68], Type: Spill, Align: 4, Size: 4
Offset: [SP-72], Type: Spill, Align: 8, Size: 4
Offset: [SP-76], Type: Variable, Align: 4, Size: 4
Offset: [SP-80], Type: Spill, Align: 4, Size: 4
Offset: [SP-84], Type: Spill, Align: 4, Size: 4
...[4 byte spills]...
Offset: [SP-1012], Type: Variable, Align: 4, Size: 4
Offset: [SP-1016], Type: Variable, Align: 4, Size: 4
[-Rpass-analysis=stack-frame-layout]

So something is very weird in FlashPoint_HandleInterrupt -- it has a
single while loop with an internal if/else if/.../else chain. So I don't
see why it would need such extensive spills...

This seems like a missed optimization in Clang, maybe?

-- 
Kees Cook