Re: [PATCH v10 0/4] Add kprobe and kretprobe support for LoongArch

[Jeff Xie]

On Fri, Dec 9, 2022 at 6:01 PM Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
>
> Hi, Masami,
>
> This series looks good to me now, but I'm not familiar with kprobes.
> So, if you have any comments, please let me know.
>
> And Jeff,
>
> As we all know, you are an expert in this domain, so could you please
> help me to test this series?
>
> If there are no objections, I plan to merge this series in a few days.
> But since the next merge window will be open soon, if there are any
> problems, I will revert the patches to wait for the next cycle.

I can't use the kprobe function normally now, tested the function from
the branch: https://github.com/loongson/linux/commits/loongarch-next

steps:
1. Try to probe __memset_fast()

[root@loongarch ]# cat /proc/kallsyms | grep __memset_fast
90000000012c75f0 T __memset_fast

./samples/kprobes/kprobe_example.c
static char symbol[KSYM_NAME_LEN] = "__memset_fast";

2. Loading the kprobe_example.ko
[root@loongarch mnt]# insmod ./kprobe_example.ko

*** The system will keep hanging ***

dmesg-messages:
gef➤  lx-dmesg
[   12.348047] handler_pre: <__memset_fast> p->addr =
0x(____ptrval____), era = 0x90000000012c75f0, estat = 0xc0000
[   12.348512] handler_post: <__memset_fast> p->addr =
0x(____ptrval____), estat = 0xc0000
[   12.348525] handler_post: <__memset_fast> p->addr =
0x(____ptrval____), estat = 0xc0000
[   12.349248] handler_pre: <__memset_fast> p->addr =
0x(____ptrval____), era = 0x90000000012c75f0, estat = 0xc0000
[   12.349259] handler_post: <__memset_fast> p->addr =
0x(____ptrval____), estat = 0xc0000

call trace:
gef➤  bt
#0  0x90000000012f45f8 in queued_spin_lock_slowpath
(lock=0x9000000001cc0018 <die_lock>, val=0x1) at
kernel/locking/qspinlock.c:383
#1  0x9000000000223b2c in die (str=str@entry=0x90000000017e3488 "Break
instruction in kernel code", regs=regs@entry=0x900000010fd735f0) at
arch/loongarch/kernel/traps.c:240
#2  0x90000000012e3968 in die_if_kernel (regs=<optimized out>,
str=<optimized out>) at ./arch/loongarch/include/asm/ptrace.h:131
#3  do_bp (regs=0x900000010fd735f0) at arch/loongarch/kernel/traps.c:485
#4  0x9000000001cb1924 in exception_handlers ()
Backtrace stopped: frame did not save the PC



> Thanks,
> Huacai
>
> On Fri, Dec 9, 2022 at 4:53 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> >
> > v10:
> >   -- Remove sign_extend() based on the latest code
> >   -- Rename insns_are_not_supported() to insns_not_supported()
> >   -- Rename insns_are_not_simulated() to insns_not_simulated()
> >   -- Set KPROBE_HIT_SSDONE if cur->post_handler is not NULL
> >   -- Enable preemption for KPROBE_REENTER in kprobe_fault_handler()
> >
> > v9:
> >   -- Rename sign_extended() to sign_extend()
> >   -- Modify kprobe_fault_handler() to handle all of kprobe_status
> >
> > v8:
> >   -- Put "regs->csr_prmd &= ~CSR_PRMD_PIE;" ahead to save one line
> >   -- Add code comment of preempt_disable()
> >   -- Put kprobe_page_fault() in __do_page_fault()
> >   -- Modify the check condition of break insn in kprobe_breakpoint_handler()
> >
> > v7:
> >   -- Remove stop_machine_cpuslocked() related code
> >
> > v6:
> >   -- Add a new patch to redefine larch_insn_patch_text() with
> >      stop_machine_cpuslocked()
> >   -- Modify kprobe_breakpoint_handler() to consider the original
> >      insn is break and return the correct value
> >   -- Modify do_bp() to refresh bcode when original insn is break
> >
> > v5:
> >   -- Rebase on the latest code
> >   -- Use stop_machine_cpuslocked() to modify insn to avoid CPU race
> >
> > v4:
> >   -- Remove kprobe_exceptions_notify() in kprobes.c
> >   -- Call kprobe_breakpoint_handler() and kprobe_singlestep_handler()
> >      in do_bp()
> >
> > v3:
> >   -- Rebase on the latest code
> >   -- Check the alignment of PC in simu_branch() and simu_pc()
> >   -- Add ibar in flush_insn_slot()
> >   -- Rename kprobe_{pre,post}_handler() to {post_}kprobe_handler
> >   -- Add preempt_disable() and preempt_enable_no_resched()
> >   -- Remove r0 save/restore and do some minor changes
> >      in kprobes_trampoline.S
> >   -- Do not enable CONFIG_KPROBES by default
> >
> > v2:
> >   -- Split simu_branch() and simu_pc() into a single patch
> >   -- Call kprobe_page_fault() in do_page_fault()
> >   -- Add kprobes_trampoline.S for kretprobe
> >
> > Tiezhu Yang (4):
> >   LoongArch: Simulate branch and PC instructions
> >   LoongArch: Add kprobe support
> >   LoongArch: Add kretprobe support
> >   samples/kprobes: Add LoongArch support
> >
> >  arch/loongarch/Kconfig                     |   2 +
> >  arch/loongarch/include/asm/inst.h          |  20 ++
> >  arch/loongarch/include/asm/kprobes.h       |  59 +++++
> >  arch/loongarch/include/asm/ptrace.h        |   1 +
> >  arch/loongarch/kernel/Makefile             |   2 +
> >  arch/loongarch/kernel/inst.c               | 123 ++++++++++
> >  arch/loongarch/kernel/kprobes.c            | 364 +++++++++++++++++++++++++++++
> >  arch/loongarch/kernel/kprobes_trampoline.S |  96 ++++++++
> >  arch/loongarch/kernel/traps.c              |  13 +-
> >  arch/loongarch/mm/fault.c                  |   3 +
> >  samples/kprobes/kprobe_example.c           |   8 +
> >  11 files changed, 687 insertions(+), 4 deletions(-)
> >  create mode 100644 arch/loongarch/include/asm/kprobes.h
> >  create mode 100644 arch/loongarch/kernel/kprobes.c
> >  create mode 100644 arch/loongarch/kernel/kprobes_trampoline.S
> >
> > --
> > 2.1.0
> >



-- 
Thanks,
JeffXie