Re: arch/powerpc/kernel/optprobes.c:34:1: error: unused function 'is_kprobe_ppc_optinsn_slot'

[Christophe Leroy]

Le 12/05/2021 à 11:36, Christophe Leroy a écrit :
> Le 11/05/2021 à 20:46, Nathan Chancellor a écrit :
> > On 5/11/2021 9:47 AM, Christophe Leroy wrote:
> > > Hi All,
> > >
> > > Le 11/05/2021 à 18:30, kernel test robot a écrit :
> > > > Hi Christophe,
> > > >
> > > > First bad commit (maybe != root cause):
> > > >
> > > > tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > > > head:   1140ab592e2ebf8153d2b322604031a8868ce7a5
> > > > commit: eacf4c0202654adfa94bbb17b5c5c77c0be14af8 powerpc: Enable OPTPROBES on PPC32
>
> Ok, the problem appears on PPC32 with that patch, but it must have been there on PPC64 since the 
> implementation of optprobes with commit 51c9c0843993 ("powerpc/kprobes: Implement Optprobes")
>
>
> > > > date:   3 weeks ago
> > > > config: powerpc-randconfig-r033-20210511 (attached as .config)
> > > > compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 
> > > > a0fed635fe1701470062495a6ffee1c608f3f1bc)
> > >
> > > A clang issue ?
> > >
> > >
> > > > 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/torvalds/linux.git/commit/?id=eacf4c0202654adfa94bbb17b5c5c77c0be14af8 
> > > >
> > > >          git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> > > >          git fetch --no-tags linus master
> > > >          git checkout eacf4c0202654adfa94bbb17b5c5c77c0be14af8
> > > >          # save the attached .config to linux build tree
> > > >          COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 ARCH=powerpc
> > > >
> > > > If you fix the issue, kindly add following tag as appropriate
> > > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > >
> > > > All errors (new ones prefixed by >>):
> > > >
> > > > > > arch/powerpc/kernel/optprobes.c:34:1: error: unused function 'is_kprobe_ppc_optinsn_slot' 
> > > > > > [-Werror,-Wunused-function]
> > > >     DEFINE_INSN_CACHE_OPS(ppc_optinsn);
> > > >     ^
> > > >     include/linux/kprobes.h:306:20: note: expanded from macro 'DEFINE_INSN_CACHE_OPS'
> > > >     static inline bool is_kprobe_##__name##_slot(unsigned long addr)        \
> > >
> > > That's a 'static inline', shouldn't generate an 'unused function' warning.
> > This is a W=1 build, which means that "inline" does not silence unused function warnings with 
> > clang because of commit 6863f5643dd7 ("kbuild: allow Clang to find unused static inline functions 
> > for W=1 build").
>
> Ok, I didn't know that.

After looking at it in more details, I don't really know what should be done to avoid that.

This unused function is defined as part of DEFINE_INSN_CACHE_OPS(ppc_optinsn).

The code uses other items defined by macro DEFINE_INSN_CACHE_OPS, so it cannot be removed.

Solution could be to hide that in a .h, but is that worth it ?

It can't go in asm/kprobes.h because linux/kprobes.h includes asm/kprobes.h before defining 
DEFINE_INSN_CACHE_OPS(). So it would mean a dedicated header just for hiding the problem under the 
carpet.

> > Cheers,
> > Nathan
> >
> > > >                        ^
> > > >     <scratch space>:16:1: note: expanded from here
> > > >     is_kprobe_ppc_optinsn_slot
> > > >     ^
> > > >     1 error generated.
> > > >
> > > >
> > > > vim +/is_kprobe_ppc_optinsn_slot +34 arch/powerpc/kernel/optprobes.c
> > > >
> > > > 51c9c084399352 Anju T 2017-02-08  20
> > > > 51c9c084399352 Anju T 2017-02-08  21  #define TMPL_CALL_HDLR_IDX    \
> > > > 51c9c084399352 Anju T 2017-02-08  22 (optprobe_template_call_handler - optprobe_template_entry)
> > > > 51c9c084399352 Anju T 2017-02-08  23  #define TMPL_EMULATE_IDX    \
> > > > 51c9c084399352 Anju T 2017-02-08  24 (optprobe_template_call_emulate - optprobe_template_entry)
> > > > 51c9c084399352 Anju T 2017-02-08  25  #define TMPL_RET_IDX        \
> > > > 51c9c084399352 Anju T 2017-02-08  26      (optprobe_template_ret - optprobe_template_entry)
> > > > 51c9c084399352 Anju T 2017-02-08  27  #define TMPL_OP_IDX        \
> > > > 51c9c084399352 Anju T 2017-02-08  28 (optprobe_template_op_address - optprobe_template_entry)
> > > > 51c9c084399352 Anju T 2017-02-08  29  #define TMPL_INSN_IDX        \
> > > > 51c9c084399352 Anju T 2017-02-08  30      (optprobe_template_insn - optprobe_template_entry)
> > > > 51c9c084399352 Anju T 2017-02-08  31  #define TMPL_END_IDX        \
> > > > 51c9c084399352 Anju T 2017-02-08  32      (optprobe_template_end - optprobe_template_entry)
> > > > 51c9c084399352 Anju T 2017-02-08  33
> > > > 51c9c084399352 Anju T 2017-02-08 @34  DEFINE_INSN_CACHE_OPS(ppc_optinsn);
> > > > 51c9c084399352 Anju T 2017-02-08  35
> > > >
> > > > :::::: The code at line 34 was first introduced by commit
> > > > :::::: 51c9c0843993528bffc920c54c2121d9e6f8b090 powerpc/kprobes: Implement Optprobes
> > > >
> > > > :::::: TO: Anju T <anju@xxxxxxxxxxxxxxxxxx>
> > > > :::::: CC: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > > >
> > > > ---
> > > > 0-DAY CI Kernel Test Service, Intel Corporation
> > > > https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx