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From:   guoren@kernel.org
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        Guo Ren <guoren@linux.alibaba.com>
Subject: [PATCH v3 0/7] riscv: Add k/uprobe supported
Date:   Mon, 13 Jul 2020 23:39:15 +0000
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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

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