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

From: Christophe Leroy
Date: Wed May 12 2021 - 05:52:39 EST




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.

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 ?

It can't go in asm/kprobes.h because linux/kprobes.h includes asm/kprobes.h before defining DEFINE_INSN_CACHE_OPS(). So it would mean a dedicated header just for hiding the problem under the carpet.



Cheers,
Nathan

                       ^
    <scratch space>:16:1: note: expanded from here
    is_kprobe_ppc_optinsn_slot
    ^
    1 error generated.


vim +/is_kprobe_ppc_optinsn_slot +34 arch/powerpc/kernel/optprobes.c

51c9c084399352 Anju T 2017-02-08  20
51c9c084399352 Anju T 2017-02-08  21  #define TMPL_CALL_HDLR_IDX    \
51c9c084399352 Anju T 2017-02-08  22 (optprobe_template_call_handler - optprobe_template_entry)
51c9c084399352 Anju T 2017-02-08  23  #define TMPL_EMULATE_IDX    \
51c9c084399352 Anju T 2017-02-08  24 (optprobe_template_call_emulate - optprobe_template_entry)
51c9c084399352 Anju T 2017-02-08  25  #define TMPL_RET_IDX        \
51c9c084399352 Anju T 2017-02-08  26      (optprobe_template_ret - optprobe_template_entry)
51c9c084399352 Anju T 2017-02-08  27  #define TMPL_OP_IDX        \
51c9c084399352 Anju T 2017-02-08  28 (optprobe_template_op_address - optprobe_template_entry)
51c9c084399352 Anju T 2017-02-08  29  #define TMPL_INSN_IDX        \
51c9c084399352 Anju T 2017-02-08  30      (optprobe_template_insn - optprobe_template_entry)
51c9c084399352 Anju T 2017-02-08  31  #define TMPL_END_IDX        \
51c9c084399352 Anju T 2017-02-08  32      (optprobe_template_end - optprobe_template_entry)
51c9c084399352 Anju T 2017-02-08  33
51c9c084399352 Anju T 2017-02-08 @34  DEFINE_INSN_CACHE_OPS(ppc_optinsn);
51c9c084399352 Anju T 2017-02-08  35

:::::: The code at line 34 was first introduced by commit
:::::: 51c9c0843993528bffc920c54c2121d9e6f8b090 powerpc/kprobes: Implement Optprobes

:::::: TO: Anju T <anju@xxxxxxxxxxxxxxxxxx>
:::::: CC: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

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