[RFC PATCH 0/8] tracing: probeevent: Improve fetcharg features

Masami Hiramatsu
2018-02-13T15:36:12Z

Hi,

This series improves probeevent variable fetcharg framework,

- Rewrite fetcharg framework with fetch_insn, switch-case based
instead of function pointer. (maybe good for retpoline)
- Add "symbol" type support, which shows symbol+offset instead of
address value.
- Add "$argN" fetcharg, which fetches function parameters.
(currently only for x86-64)
- Add array type support for basic types (except for string),
which enables to get fixed length array from probeevents.

All ideas came from Steve's function event tracer. Thanks Steve!

I'll add string (pointer) array support and testcases for these
features in the next version.

Here are examples:

o 'symbol' type

# echo 'p vfs_read $stack0:symbol' > kprobe_events
# echo 1 > events/kprobes/p_vfs_read_0/enable
# tail -n 3 trace
sh-729 [007] ...2 105.753637: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=SyS_read+0x42/0x90
tail-736 [000] ...2 105.754904: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=kernel_read+0x2c/0x40
tail-736 [000] ...2 105.754929: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=kernel_read+0x2c/0x40

o $argN

# echo 'p vfs_read $arg0 $arg1 $arg2' > kprobe_events
# echo 1 > events/kprobes/p_vfs_read_0/enable
# tail -n 3 trace
sh-726 [007] ...2 134.288973: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=0xffff88001d98ec00 arg2=0x7ffeb4330f79 arg3=0x1
tail-731 [000] ...2 134.289987: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=0xffff88001d9dd200 arg2=0xffff88001d8a0a00 arg3=0x80
tail-731 [000] ...2 134.290016: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=0xffff88001d9dd200 arg2=0xffff88001faf4a00 arg3=0x150

o Array type

# echo 'p vfs_read +0($stack):x64 +0($stack):x8[8]' > kprobe_events
# echo 1 > events/kprobes/p_vfs_read_0/enable
# tail -n 3 trace
sh-729 [007] ...2 91.701664: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=0xffffffff811b1252 arg2={0x52,0x12,0x1b,0x81,0xff,0xff,0xff,0xff}
tail-734 [000] ...2 91.702366: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=0xffffffff811b0dec arg2={0xec,0xd,0x1b,0x81,0xff,0xff,0xff,0xff}
tail-734 [000] ...2 91.702386: p_vfs_read_0: (vfs_read+0x0/0x130) arg1=0xffffffff811b0dec arg2={0xec,0xd,0x1b,0x81,0xff,0xff,0xff,0xff}
#
# cat events/kprobes/p_vfs_read_0/format
name: p_vfs_read_0
ID: 1069
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;

field:unsigned long __probe_ip; offset:8; size:8; signed:0;
field:u64 arg1; offset:16; size:0; signed:0;
field:u8 arg2[8]; offset:24; size:8; signed:0;

print fmt: "(%lx) arg1=0x%Lx arg2={0x%x,0x%x,0x%x,0x%x,0x%x,0x%x,0x%x,0x%x}", REC->__probe_ip, REC->arg1, REC->arg2[0], REC->arg2[1], REC->arg2[2], REC->arg2[3], REC->arg2[4], REC->arg2[5], REC->arg2[6], REC->arg2[7]

Thanks,

---

Masami Hiramatsu (8):
tracing: probeevent: Cleanup print argument functions
tracing: probeevent: Cleanup argument field definition
tracing: probeevent: Remove NOKPROBE_SYMBOL from print functions
tracing: probeevent: Introduce new argument fetching code
tracing: probeevent: Add symbol type
x86: ptrace: Add function argument access API
tracing: probeevent: Add $argN for accessing function args
tracing: probeevent: Add an array for basic types

Documentation/trace/kprobetrace.txt | 20 +
arch/Kconfig | 7
arch/x86/Kconfig | 1
arch/x86/include/asm/ptrace.h | 38 ++
kernel/trace/trace_kprobe.c | 396 +++++++++--------------
kernel/trace/trace_probe.c | 614 ++++++++++++++++-------------------
kernel/trace/trace_probe.h | 313 +++++++++---------
kernel/trace/trace_uprobe.c | 188 ++++++-----
8 files changed, 771 insertions(+), 806 deletions(-)

--
Masami Hiramatsu (Linaro) <mhiramat@kernel.org>