ktap

A New Scripting Dynamic Tracing Tool For Linux
www.ktap.org

ktap is a new scripting dynamic tracing tool for Linux, it uses a scripting language and lets users trace the Linux kernel dynamically. ktap is designed to give operational insights with interoperability that allows users to tune, troubleshoot and extend the kernel and applications. It's similar to Linux Systemtap and Solaris Dtrace.

ktap has different design principles from Linux mainstream dynamic tracing language in that it's based on bytecode, so it doesn't depend upon GCC, doesn't require compiling kernel module for each script, safe to use in production environment, fulfilling the embedded ecosystem's tracing needs.

More information can be found at ktap homepage.

Highlights

a simple but powerful scripting language
register based interpreter (heavily optimized) in Linux kernel
small and lightweight
not depend on the gcc toolchain for each script run
easy to use in embedded environments without debugging info
support for tracepoint, kprobe, uprobe, function trace, timer, and more
supported in x86, arm, ppc, mips
safety in sandbox

Building & Running

Clone ktap from github

 $ git clone http://github.com/ktap/ktap.git

Compiling ktap

 $ cd ktap
 $ make       #generate ktapvm kernel module and ktap binary

Load ktapvm kernel module(make sure debugfs mounted)

 $ make load  #need to be root or have sudo access

Running ktap
```
 $ ./ktap samples/helloworld.kp
```

Examples

simplest one-liner command to enable all tracepoints
```
 ktap -e "trace *:* { print(argstr) }"
```

syscall tracing on target process

 ktap -e "trace syscalls:* { print(argstr) }" -- ls

ftrace(kernel newer than 3.3, and must compiled with CONFIG_FUNCTION_TRACER)

 ktap -e "trace ftrace:function { print(argstr) }"

 ktap -e "trace ftrace:function /ip==mutex*/ { print(argstr) }"

simple syscall tracing

 trace syscalls:* {
         print(cpu, pid, execname, argstr)
 }

syscall tracing in histogram style

 var s = {}

 trace syscalls:sys_enter_* {
         s[probename] += 1
 }

 trace_end {
         print_hist(s)
 }

kprobe tracing

 trace probe:do_sys_open dfd=%di fname=%dx flags=%cx mode=+4($stack) {
         print("entry:", execname, argstr)
 }

 trace probe:do_sys_open%return fd=$retval {
         print("exit:", execname, argstr)
 }

uprobe tracing

 trace probe:/lib/libc.so.6:malloc {
         print("entry:", execname, argstr)
 }

 trace probe:/lib/libc.so.6:malloc%return {
         print("exit:", execname, argstr)
 }

stapsdt tracing (userspace static marker)

 trace sdt:/lib64/libc.so.6:lll_futex_wake {
         print("lll_futex_wake", execname, argstr)
 }

 or:

 #trace all static mark in libc
 trace sdt:/lib64/libc.so.6:* {
         print(execname, argstr)
 }

timer

 tick-1ms {
         printf("time fired on one cpu\n");
 }

 profile-2s {
         printf("time fired on every cpu\n");
 }

FFI (Call kernel function from ktap script, need to compile with FFI=1)

ffi.cdef[[
        int printk(char *fmt, ...);
]]

ffi.C.printk("This message is called from ktap ffi\n")

More examples can be found at samples directory.

Mailing list

ktap@freelists.org
You can subscribe to ktap mailing list at link (subscribe before posting): http://www.freelists.org/list/ktap

Copyright and License

ktap is licensed under GPL v2

Contribution

ktap is still under active development, so contributions are welcome. You are encouraged to report bugs, provide feedback, send feature request, or hack on it.

See More

More info can be found at [documentation][tutorial] [tutorial]: http://www.ktap.org/doc/tutorial.html

ackalker/ktap