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

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Date:   Wed, 12 May 2021 17:12:32 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Masami Hiramatsu <mhiramat@...nel.org>
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'



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.



> 
>  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

>   
>   	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