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

[Masami Hiramatsu]

On Wed, 12 May 2021 21:50:57 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> On Wed, 12 May 2021 11:52:30 +0200
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> wrote:

> > 
> > 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.
> 
> Ah, thanks for reporting!
> 
> > 
> > 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 ?
> 
> The best solution is to remove ppc_optinsn, but that is defined in kernel/kprobes.c
> just because page allocation is different.
> I think the easiest fix is to add weak alloc_optinsn_page() and override it
> in arch/powerpc/kernel/optprobe.c.

Please try this patch.

Thank you,