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Date:   Tue, 14 Jul 2020 20:23:46 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     guoren@kernel.org
Cc:     palmerdabbelt@google.com, paul.walmsley@sifive.com,
        oleg@redhat.com, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, anup@brainfault.org,
        linux-csky@vger.kernel.org, greentime.hu@sifive.com,
        zong.li@sifive.com, me@packi.ch, bjorn.topel@gmail.com,
        Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH v3 0/7] riscv: Add k/uprobe supported
Message-Id: <20200714202346.0911e9475bf30a30d0d36b67@kernel.org>
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Hi Guo,

On Mon, 13 Jul 2020 23:39:15 +0000
guoren@kernel.org wrote:

> From: Guo Ren <guoren@linux.alibaba.com>
> 
> The patchset includes kprobe/uprobe support and some related fixups.
> Patrick provides HAVE_REGS_AND_STACK_ACCESS_API support and some
> kprobe's code. The framework of k/uprobe is from csky but also refers
> to other arches'. kprobes on ftrace is also supported in the patchset.
> 
> There is no single step exception in riscv ISA, only single-step
> facility for jtag. See riscv-Privileged spec:
> 
> Interrupt Exception Code-Description
> 1 0 Reserved
> 1 1 Supervisor software interrupt
> 1 2–4 Reserved
> 1 5 Supervisor timer interrupt
> 1 6–8 Reserved
> 1 9 Supervisor external interrupt
> 1 10–15 Reserved
> 1 ≥16 Available for platform use
> 0 0 Instruction address misaligned
> 0 1 Instruction access fault
> 0 2 Illegal instruction
> 0 3 Breakpoint
> 0 4 Load address misaligned
> 0 5 Load access fault
> 0 6 Store/AMO address misaligned
> 0 7 Store/AMO access fault
> 0 8 Environment call from U-mode
> 0 9 Environment call from S-mode
> 0 10–11 Reserved
> 0 12 Instruction page fault
> 0 13 Load page fault
> 0 14 Reserved
> 0 15 Store/AMO page fault
> 0 16–23 Reserved
> 0 24–31 Available for custom use
> 0 32–47 Reserved
> 0 48–63 Available for custom use
> 0 ≥64 Reserved
> 
> No single step!
> 
> Other arches use hardware single-step exception for k/uprobe,  eg:
>  - powerpc: regs->msr |= MSR_SINGLESTEP
>  - arm/arm64: PSTATE.D for enabling software step exceptions
>  - s390: Set PER control regs, turns on single step for the given address
>  - x86: regs->flags |= X86_EFLAGS_TF
>  - csky: of course use hw single step :)
> 
> All the above arches use a hardware single-step exception
> mechanism to execute the instruction that was replaced with a probe
> breakpoint. So utilize ebreak to simulate.
> 
> Some pc related instructions couldn't be executed out of line and some
> system/fence instructions couldn't be a trace site at all. So we give
> out a reject list and simulate list in decode-insn.c.
> 
> You could use uprobe to test simulate code like this:
> 
>  echo 'p:enter_current_state_one /hello:0x6e4 a0=%a0 a1=%a1' >> /sys/kernel/debug/tracing/uprobe_events
>  echo 1 > /sys/kernel/debug/tracing/events/uprobes/enable
>  /hello
>  ^C
>  cat /sys/kernel/debug/tracing/trace
>  tracer: nop
> 
>  entries-in-buffer/entries-written: 1/1   #P:1
> 
>                               _-----=> irqs-off
>                              / _----=> need-resched
>                             | / _---=> hardirq/softirq
>                             || / _--=> preempt-depth
>                             ||| /     delay
>            TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
>               | |       |   ||||       |         |
>           hello-94    [000] d...    55.404242: enter_current_state_one: (0x106e4) a0=0x1 a1=0x3fffa8ada8
> 
> Be care /hello:0x6e4 is the file offset in elf and it relate to 0x106e4
> in memory and hello is your target elf program.
> 
> Try kprobe like this:
> 
>  echo 'p:myprobe _do_fork dfd=%a0 filename=%a1 flags=%a2 mode=+4($stack)' > /sys/kernel/debug/tracing/kprobe_events
>  echo 'r:myretprobe _do_fork $retval' >> /sys/kernel/debug/tracing/kprobe_event
> 
>  echo 1 >/sys/kernel/debug/tracing/events/kprobes/enable
>  cat /sys/kernel/debug/tracing/trace
>  tracer: nop
> 
>  entries-in-buffer/entries-written: 2/2   #P:1
> 
>                               _-----=> irqs-off
>                              / _----=> need-resched
>                             | / _---=> hardirq/softirq
>                             || / _--=> preempt-depth
>                             ||| /     delay
>            TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
>               | |       |   ||||       |         |
>              sh-92    [000] .n..   131.804230: myprobe: (_do_fork+0x0/0x2e6) dfd=0xffffffe03929fdf8 filename=0x0 flags=0x101000 mode=0x1200000ffffffe0
>              sh-92    [000] d...   131.806607: myretprobe: (__do_sys_clone+0x70/0x82 <- _do_fork) arg1=0x5f
>  cat /sys/kernel/debug/tracing/trace

Thank you for your great work!

BTW, could you also run the ftracetest and boot-time smoke test on it?
You can find it under tools/testing/selftests/ftrace, and
CONFIG_KPROBES_SANITY_TEST.
It will ensure that your patch is correctly ported.

Thank you,

> 
> Changlog v3:
>  - Add upport for function error injection
>  - Fixup kprobes handler couldn't change pc
> 
> Changlog v2:
>  - Add Reviewed-by, Tested-by, Acked-by, thx for all of you
>  - Add kprobes on ftrace feature
>  - Use __always_inline as same as fix_to_virt for fixup
>    BUILD_BUG_ON
>  - Use const "const unsigned int" for 2th param for fixup
>    BUILD_BUG_ON
> 
> Guo Ren (6):
>   riscv: Fixup compile error BUILD_BUG_ON failed
>   riscv: Fixup kprobes handler couldn't change pc
>   riscv: Add kprobes supported
>   riscv: Add uprobes supported
>   riscv: Add KPROBES_ON_FTRACE supported
>   riscv: Add support for function error injection
> 
> Patrick Stählin (1):
>   RISC-V: Implement ptrace regs and stack API
> 
>  arch/riscv/Kconfig                            |   8 +
>  arch/riscv/include/asm/kprobes.h              |  40 +++
>  arch/riscv/include/asm/probes.h               |  24 ++
>  arch/riscv/include/asm/processor.h            |   1 +
>  arch/riscv/include/asm/ptrace.h               |  35 ++
>  arch/riscv/include/asm/thread_info.h          |   4 +-
>  arch/riscv/include/asm/uprobes.h              |  40 +++
>  arch/riscv/kernel/Makefile                    |   1 +
>  arch/riscv/kernel/mcount-dyn.S                |   3 +-
>  arch/riscv/kernel/patch.c                     |   8 +-
>  arch/riscv/kernel/probes/Makefile             |   6 +
>  arch/riscv/kernel/probes/decode-insn.c        |  48 +++
>  arch/riscv/kernel/probes/decode-insn.h        |  18 +
>  arch/riscv/kernel/probes/ftrace.c             |  52 +++
>  arch/riscv/kernel/probes/kprobes.c            | 471 ++++++++++++++++++++++++++
>  arch/riscv/kernel/probes/kprobes_trampoline.S |  93 +++++
>  arch/riscv/kernel/probes/simulate-insn.c      |  85 +++++
>  arch/riscv/kernel/probes/simulate-insn.h      |  47 +++
>  arch/riscv/kernel/probes/uprobes.c            | 186 ++++++++++
>  arch/riscv/kernel/ptrace.c                    |  99 ++++++
>  arch/riscv/kernel/signal.c                    |   3 +
>  arch/riscv/kernel/traps.c                     |  19 ++
>  arch/riscv/lib/Makefile                       |   2 +
>  arch/riscv/lib/error-inject.c                 |  10 +
>  arch/riscv/mm/fault.c                         |  11 +
>  25 files changed, 1310 insertions(+), 4 deletions(-)
>  create mode 100644 arch/riscv/include/asm/probes.h
>  create mode 100644 arch/riscv/include/asm/uprobes.h
>  create mode 100644 arch/riscv/kernel/probes/Makefile
>  create mode 100644 arch/riscv/kernel/probes/decode-insn.c
>  create mode 100644 arch/riscv/kernel/probes/decode-insn.h
>  create mode 100644 arch/riscv/kernel/probes/ftrace.c
>  create mode 100644 arch/riscv/kernel/probes/kprobes.c
>  create mode 100644 arch/riscv/kernel/probes/kprobes_trampoline.S
>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.c
>  create mode 100644 arch/riscv/kernel/probes/simulate-insn.h
>  create mode 100644 arch/riscv/kernel/probes/uprobes.c
>  create mode 100644 arch/riscv/lib/error-inject.c
> 
> -- 
> 2.7.4
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>