linux-kernel - Re: [PATCH V3 3/4] arch/powerpc: Implement Optprobes

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Date:   Tue, 31 Jan 2017 07:43:35 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Anju T Sudhakar <anju@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     ananth@...ibm.com, naveen.n.rao@...ux.vnet.ibm.com,
        paulus@...ba.org, srikar@...ux.vnet.ibm.com,
        benh@...nel.crashing.org, mahesh@...ux.vnet.ibm.com,
        mhiramat@...nel.org, anju@...ux.vnet.ibm.com
Subject: Re: [PATCH V3 3/4] arch/powerpc: Implement Optprobes

Anju T Sudhakar <anju@...ux.vnet.ibm.com> writes:

> Detour buffer contains instructions to create an in memory pt_regs.
> After the execution of the pre-handler, a call is made for instruction emulation.
> The NIP is determined in advanced through dummy instruction emulation and a branch
> instruction is created to the NIP at the end of the trampoline.
>
> Instruction slot for detour buffer is allocated from the reserved area.
> For the time being, 64KB is reserved in memory for this purpose.
>
> Instructions which can be emulated using analyse_instr() are suppliants
> for optimization. Before optimization ensure that the address range
> between the detour buffer allocated and the instruction being probed
> is within ± 32MB.
>
> Signed-off-by: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> ---
>  .../features/debug/optprobes/arch-support.txt      |   2 +-
>  arch/powerpc/Kconfig                               |   1 +
>  arch/powerpc/include/asm/kprobes.h                 |  24 +-
>  arch/powerpc/include/asm/sstep.h                   |   1 +
>  arch/powerpc/kernel/Makefile                       |   1 +
>  arch/powerpc/kernel/optprobes.c                    | 331 +++++++++++++++++++++
>  arch/powerpc/kernel/optprobes_head.S               | 135 +++++++++
>  arch/powerpc/lib/sstep.c                           |  21 ++
>  8 files changed, 514 insertions(+), 2 deletions(-)
>  create mode 100644 arch/powerpc/kernel/optprobes.c
>  create mode 100644 arch/powerpc/kernel/optprobes_head.S

This breaks the pseries_defconfig (at least) build:

  In file included from ../include/linux/kprobes.h:45:0,
                   from ../arch/powerpc/kernel/optprobes.c:12:
  ../arch/powerpc/kernel/optprobes.c: In function ‘arch_prepare_optimized_kprobe’:
  ../arch/powerpc/include/asm/kprobes.h:79:16: error: ‘MODULE_NAME_LEN’ undeclared (first use in this function)
    char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];  \
                  ^
  ../arch/powerpc/kernel/optprobes.c:230:2: note: in expansion of macro ‘kprobe_lookup_name’
    kprobe_lookup_name("optimized_callback", op_callback_addr);
    ^~~~~~~~~~~~~~~~~~
  ../arch/powerpc/include/asm/kprobes.h:79:16: note: each undeclared identifier is reported only once for each function it appears in
    char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];  \
                  ^
  ../arch/powerpc/kernel/optprobes.c:230:2: note: in expansion of macro ‘kprobe_lookup_name’
    kprobe_lookup_name("optimized_callback", op_callback_addr);
    ^~~~~~~~~~~~~~~~~~
  ../arch/powerpc/include/asm/kprobes.h:82:14: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
    if ((modsym = strchr(name, ':')) != NULL) {   \
                ^
  ../arch/powerpc/kernel/optprobes.c:230:2: note: in expansion of macro ‘kprobe_lookup_name’
    kprobe_lookup_name("optimized_callback", op_callback_addr);
    ^~~~~~~~~~~~~~~~~~
  ../arch/powerpc/include/asm/kprobes.h:79:7: error: unused variable ‘dot_name’ [-Werror=unused-variable]
    char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];  \
         ^
  ../arch/powerpc/kernel/optprobes.c:230:2: note: in expansion of macro ‘kprobe_lookup_name’
    kprobe_lookup_name("optimized_callback", op_callback_addr);
    ^~~~~~~~~~~~~~~~~~
  ../arch/powerpc/include/asm/kprobes.h:82:14: error: assignment discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
    if ((modsym = strchr(name, ':')) != NULL) {   \
                ^
  ../arch/powerpc/kernel/optprobes.c:231:2: note: in expansion of macro ‘kprobe_lookup_name’
    kprobe_lookup_name("emulate_step", emulate_step_addr);
    ^~~~~~~~~~~~~~~~~~
  ../arch/powerpc/include/asm/kprobes.h:79:7: error: unused variable ‘dot_name’ [-Werror=unused-variable]
    char dot_name[MODULE_NAME_LEN + 1 + KSYM_NAME_LEN];  \
         ^
  ../arch/powerpc/kernel/optprobes.c:231:2: note: in expansion of macro ‘kprobe_lookup_name’
    kprobe_lookup_name("emulate_step", emulate_step_addr);
    ^~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors
  make[2]: *** [arch/powerpc/kernel/optprobes.o] Error 1
  make[2]: *** Waiting for unfinished jobs....
  make[1]: *** [arch/powerpc/kernel] Error 2
  make[1]: *** Waiting for unfinished jobs....
  make: *** [sub-make] Error 2


This may not be your bug, but your patch exposes it unfortunately.

cheers