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

[Christophe Leroy]

Le 12/05/2021 à 17:06, Masami Hiramatsu a écrit :
> 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,


Yeah, look pretty similar to the two patches I sent 30 minutes ago.



>  From 7782fa154349923ed52baa8843cc1d5eed26e82d Mon Sep 17 00:00:00 2001
> From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> 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

>   
>   	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