linux-kernel - Re: arch/powerpc/kernel/optprobes.c:34:1: error: unused function 'is_kprobe_ppc_optinsn

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Message-Id: <20210512215057.6875aeaf67fb31495ab29987@kernel.org>
Date:   Wed, 12 May 2021 21:50:57 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        kernel test robot <lkp@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        kbuild-all@...ts.01.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: arch/powerpc/kernel/optprobes.c:34:1: error: unused function
 'is_kprobe_ppc_optinsn_slot'

On Wed, 12 May 2021 11:52:30 +0200
Christophe Leroy <christophe.leroy@...roup.eu> 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@...el.com>
> >>>>
> >>>> 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.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>