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

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Message-Id: <20170131075536.GA3824@naverao1-tp.localdomain>
Date:   Tue, 31 Jan 2017 13:25:37 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Anju T Sudhakar <anju@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ananth@...ibm.com, paulus@...ba.org, srikar@...ux.vnet.ibm.com,
        benh@...nel.crashing.org, mahesh@...ux.vnet.ibm.com,
        mhiramat@...nel.org
Subject: Re: [PATCH V3 3/4] arch/powerpc: Implement Optprobes

On 2017/01/31 07:43AM, Michael Ellerman wrote:
> 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.

Sorry for the trouble, we should have caught this.

- Naveen