Re: [linux-next:master 4044/9592] arch/arm/kernel/ftrace.c:229:6: warning: no previous prototype for function 'prepare_ftrace_return'

[Ard Biesheuvel <ardb@kernel.org>]

(cc Rong Chen)

On Wed, 2 Mar 2022 at 03:52, kernel test robot <lkp@intel.com> wrote:
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   e6ada6df471f847da3b09b357e246c62335bc0bb
> commit: 41918ec82eb6f80c8b401422f27ca76c85aa0cb7 [4044/9592] ARM: ftrace: enable the graph tracer with the EABI unwinder
> config: arm-bcm2835_defconfig (https://download.01.org/0day-ci/archive/20220302/202203020913.I6LbmH7l-lkp@intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project d271fc04d5b97b12e6b797c6067d3c96a8d7470e)
> 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 arm cross compiling tool for clang build
>         # apt-get install binutils-arm-linux-gnueabi
>         # https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=41918ec82eb6f80c8b401422f27ca76c85aa0cb7
>         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 41918ec82eb6f80c8b401422f27ca76c85aa0cb7
>         # save the config file to linux build tree
>         mkdir build_dir
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=arm SHELL=/bin/bash arch/arm/kernel/
>
> 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 >>):
>
> >> arch/arm/kernel/ftrace.c:229:6: warning: no previous prototype for function 'prepare_ftrace_return' [-Wmissing-prototypes]
>    void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
>         ^
>    arch/arm/kernel/ftrace.c:229:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
>    void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
>    ^
>    static
>    1 warning generated.
>

This function is asmlinkage so why is this still being reported?


>
> vim +/prepare_ftrace_return +229 arch/arm/kernel/ftrace.c
>
> 376cfa8730c08c0 Tim Bird                2010-10-09  226
> 376cfa8730c08c0 Tim Bird                2010-10-09  227  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  228  asmlinkage
> 376cfa8730c08c0 Tim Bird                2010-10-09 @229  void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  230                            unsigned long frame_pointer,
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  231                            unsigned long stack_pointer)
> 376cfa8730c08c0 Tim Bird                2010-10-09  232  {
> 376cfa8730c08c0 Tim Bird                2010-10-09  233         unsigned long return_hooker = (unsigned long) &return_to_handler;
> 376cfa8730c08c0 Tim Bird                2010-10-09  234         unsigned long old;
> 376cfa8730c08c0 Tim Bird                2010-10-09  235
> 376cfa8730c08c0 Tim Bird                2010-10-09  236         if (unlikely(atomic_read(&current->tracing_graph_pause)))
> 376cfa8730c08c0 Tim Bird                2010-10-09  237                 return;
> 376cfa8730c08c0 Tim Bird                2010-10-09  238
> 953f534a7ed6b72 Ard Biesheuvel          2022-01-25  239         if (IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER)) {
> 953f534a7ed6b72 Ard Biesheuvel          2022-01-25  240                 /* FP points one word below parent's top of stack */
> 953f534a7ed6b72 Ard Biesheuvel          2022-01-25  241                 frame_pointer += 4;
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  242         } else {
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  243                 struct stackframe frame = {
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  244                         .fp = frame_pointer,
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  245                         .sp = stack_pointer,
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  246                         .lr = self_addr,
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  247                         .pc = self_addr,
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  248                 };
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  249                 if (unwind_frame(&frame) < 0)
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  250                         return;
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  251                 if (frame.lr != self_addr)
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  252                         parent = frame.lr_addr;
> 41918ec82eb6f80 Ard Biesheuvel          2022-01-25  253                 frame_pointer = frame.sp;
> 953f534a7ed6b72 Ard Biesheuvel          2022-01-25  254         }
> 953f534a7ed6b72 Ard Biesheuvel          2022-01-25  255
> 376cfa8730c08c0 Tim Bird                2010-10-09  256         old = *parent;
> 376cfa8730c08c0 Tim Bird                2010-10-09  257         *parent = return_hooker;
> 376cfa8730c08c0 Tim Bird                2010-10-09  258
> f1f5b14afd7cce3 Steven Rostedt (VMware  2018-11-18  259)        if (function_graph_enter(old, self_addr, frame_pointer, NULL))
> 376cfa8730c08c0 Tim Bird                2010-10-09  260                 *parent = old;
> 376cfa8730c08c0 Tim Bird                2010-10-09  261  }
> dd686eb13959e49 Rabin Vincent           2010-11-06  262
>
> :::::: The code at line 229 was first introduced by commit
> :::::: 376cfa8730c08c0394d0aa1d4a80fd8c9971f323 ARM: ftrace: function graph tracer support
>
> :::::: TO: Tim Bird <tim.bird@am.sony.com>
> :::::: CC: Rabin Vincent <rabin@rab.in>
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org