Re: [PATCH v12 00/10] arm64: Add kernel probes (kprobes) support

[James Morse]

Hi David,

On 27/04/16 19:52, David Long wrote:
> From: "David A. Long" <dave.long@xxxxxxxxxx>
> 
> This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches,
> first seen in October 2013. This version attempts to address concerns raised by
> reviewers and also fixes problems discovered during testing.
> 
> This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
> and return probes(kretprobes) support for ARM64.
> 
> The kprobes mechanism makes use of software breakpoint and single stepping
> support available in the ARM v8 kernel.

I applied this series on v4.6-rc7, and built the sample kprobes. They work fine,
unless I throw ftrace into the mix too.

I enabled the function_graph tracer, then tried to load the jprobe example module:
-------------------------%<-------------------------
root@ubuntu:/sys/kernel/debug/tracing# insmod /root/jprobe_example.ko
Planted jprobe at ffffff80080c8f20, handler addr ffffff8000bb3000
root@ubuntu:/sys/kernel/debug/tracing# jprobe: clone_flags = 0x1200011, stack_st
art = 0x0 stack_size = 0x0
Bad mode in Synchronous Abort handler detected, code 0x86000005 -- IABT (current
 EL)
CPU: 5 PID: 1047 Comm: systemd-udevd Not tainted 4.6.0-rc7+ #4064
Hardware name: ARM Juno development board (r1) (DT)
task: ffffffc975948300 ti: ffffffc974e4c000 task.ti: ffffffc974e4c000
PC is at 0x0
LR is at 0x0

pc : [<0000000000000000>] lr : [<0000000000000000>] pstate: 60000145
sp : ffffffc974e4ff00
x29: 0000000001200011 x28: ffffffc974e4c000
x27: ffffff80088d0000 x26: 00000000000000dc
x25: 0000000000000120 x24: 0000000000000015
x23: 0000000060000000 x22: 0000007fa1b40e60
x21: 0000007fa1ce70d0 x20: 0000000000000000
x19: 0000000000000000 x18: 0000000000000a03
x17: 0000007fa1b40d90 x16: ffffff80080c9708
x15: 003b9aca00000000 x14: 0000007fddb7e5c0
x13: 0000007fa1b40e2c x12: 0000000000d00ff0
x11: ffffff8009c4d000 x10: ffffff800920c000
x9 : ffffff8008f5c000 x8 : ffffffc976c06800
x7 : 000000000006daf2 x6 : 0000000000000015
x5 : 0000000000000004 x4 : ffffffc96e8690a0
x3 : 0000001ed7cbab74 x2 : ffffffc96e869000
x1 : 0000000000000000 x0 : 0000000000000000

Internal error: Oops - bad mode: 0 [#1] PREEMPT SMP
Modules linked in: jprobe_example
CPU: 5 PID: 1047 Comm: systemd-udevd Not tainted 4.6.0-rc7+ #4064
Hardware name: ARM Juno development board (r1) (DT)
task: ffffffc975948300 ti: ffffffc974e4c000 task.ti: ffffffc974e4c000
PC is at 0x0
LR is at 0x0

pc : [<0000000000000000>] lr : [<0000000000000000>] pstate: 60000145
sp : ffffffc974e4ff00
x29: 0000000001200011 x28: ffffffc974e4c000
x27: ffffff80088d0000 x26: 00000000000000dc
x25: 0000000000000120 x24: 0000000000000015
x23: 0000000060000000 x22: 0000007fa1b40e60
x21: 0000007fa1ce70d0 x20: 0000000000000000
x19: 0000000000000000 x18: 0000000000000a03
x17: 0000007fa1b40d90 x16: ffffff80080c9708
x15: 003b9aca00000000 x14: 0000007fddb7e5c0
x13: 0000007fa1b40e2c x12: 0000000000d00ff0
x11: ffffff8009c4d000 x10: ffffff800920c000
x9 : ffffff8008f5c000 x8 : ffffffc976c06800
x7 : 000000000006daf2 x6 : 0000000000000015
x5 : 0000000000000004 x4 : ffffffc96e8690a0
x3 : 0000001ed7cbab74 x2 : ffffffc96e869000
x1 : 0000000000000000 x0 : 0000000000000000

Process systemd-udevd (pid: 1047, stack limit = 0xffffffc974e4c020)
Stack: (0xffffffc974e4ff00 to 0xffffffc974e50000)
ff00: 0000000000000417 0000007fa1ce76f0 00000000000000dc 0000000000000417
ff20: 00000000ffffffff 0000007fddb7ecf8 0000000000000005 ffffffffffffffff
ff40: 00000000ff000001 003b9aca00000000 000000555b3868b0 0000007fa1b40d90
ff60: 0000000000000a03 0000007fddb7e5c0 0000000000000000 0000007fddb7e5e0
ff80: 000000555b358000 000000558f56f0e0 0000000000000000 000000558f574f00
ffa0: 000000558f574f00 00000000000004fa 000000558f56f010 0000007fddb7e600
ffc0: 0000007fa1b40e2c 0000007fddb7e5c0 0000007fa1b40e60 0000000060000000
ffe0: 0000000001200011 00000000000000dc 0004000084000200 0800000002000000
Call trace:
[<          (null)>]           (null)
Code: bad PC value
---[ end trace 35d24aad799c2941 ]---
-------------------------%<-------------------------


Thanks,


James