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Date: Thu, 13 May 2021 08:42:39 +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 17:12:32 +0200
Christophe Leroy <christophe.leroy@...roup.eu> wrote:
>
>
> Le 12/05/2021 à 17:06, Masami Hiramatsu a écrit :
> > On Wed, 12 May 2021 21:50:57 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> >> 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.
> >
> > Please try this patch.
> >
> > Thank you,
>
>
> Yeah, look pretty similar to the two patches I sent 30 minutes ago.
Ah, I missed it.
OK, let me check.
>
>
>
> >
> > From 7782fa154349923ed52baa8843cc1d5eed26e82d Mon Sep 17 00:00:00 2001
> > From: Masami Hiramatsu <mhiramat@...nel.org>
> > Date: Wed, 12 May 2021 23:33:10 +0900
> > Subject: [PATCH] powerpc/kprobes: Define arch specific optinsn memory
> > allocation
> >
>
> > @@ -203,14 +193,14 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
> > unsigned long nip, size;
> > int rc, i;
> >
> > - kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
> > + kprobe_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
>
> Is this still needed ? It looks like it is already done by init_kprobes() in kernel/kprobes.c
No, not needed anymore.
Thanks!
>
> >
> > nip = can_optimize(p);
> > if (!nip)
> > return -EILSEQ;
> >
> > /* Allocate instruction slot for detour buffer */
> > - buff = get_ppc_optinsn_slot();
> > + buff = get_optinsn_slot();
> > if (!buff)
> > return -ENOMEM;
> >
>
> Christophe
--
Masami Hiramatsu <mhiramat@...nel.org>
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