Messages in this thread Patch in this message | | | Date | Mon, 28 Sep 2020 12:08:08 +0200 | From | Jiri Olsa <> | Subject | Re: perf script, libperf: python binding bug (bytearrays vs. strings) |
| |
On Sun, Sep 27, 2020 at 09:43:12AM +0200, Hagen Paul Pfeifer wrote: > Hallo Jiri, Arnaldo, > > after updating Debian (probably with the advent of Python 3.8.5, guessing) > I get a wired behavior with python scripting. The error is that the python type > for prev_comm and next_comm are not strings anymore, rather bytearrays. Which > are incompatible types and scripts will not work anymore. NOTE: common_comm is > still fine (see swapper & mutex-thread-co), so they must be treated internal > differently compared to prev_comm and next_comm and possibly show a way to solve > this problem! > > After bisecting the kernel (perf) even back to v5.6 the problem still exist. > Compiling perf with PYTHON=python2 do not show any problems - no problems in > the Python2 world. So I assume with Python 3.8.5 (or other helper library) > something changed internally. I assume the cause exists in perf forever but > is now triggered with the new Python3 version. > > How to reproduce: > > make PYTHON=python3 > ./perf record -e sched:sched_switch -a -- sleep 5 > ./perf script --gen-script py > ./perf script -s ./perf-script.py > > [..] > sched__sched_switch 7 563231.759525792 0 swapper prev_comm=bytearray(b'swapper/7\x00\x00\x00\x00\x00\x00\x00'), prev_pid=0, prev_prio=120, prev_state=, next_comm=bytearray(b'mutex-thread-co\x00'), next_pid=3447985, next_prio=120 > Sample: {addr=0, cpu=7, datasrc=84410401, datasrc_decode=N/A|SNP N/A|TLB N/A|LCK N/A, ip=18446744072189289569, period=1, phys_addr=0, pid=0, tid=0, time=563231759525792, transaction=0, values=[(0, 0)], weight=0} > > sched__sched_switch 7 563231.759582596 3447985 mutex-thread-co prev_comm=bytearray(b'mutex-thread-co\x00'), prev_pid=3447985, prev_prio=120, prev_state=, next_comm=bytearray(b'swapper/7\x00\x00\x00\x00\x00\x00\x00'), next_pid=0, next_prio=120 > Sample: {addr=0, cpu=7, datasrc=84410401, datasrc_decode=N/A|SNP N/A|TLB N/A|LCK N/A, ip=18446744072189289569, period=1, phys_addr=0, pid=3447983, tid=3447985, time=563231759582596, transaction=0, values=[(0, 0)], weight=0} > > > See =bytearray(b'swapper/7\x00\x00\x00\x00\x00\x00\x00') - should be swapper/7 > > > Note: the byte array has the length of 16 - exactly like the kernel > (TASK_COMM_LEN). I assume this is somehow copied directly into the variables > and not stringified anymore. > > > Even worse: I discovered bytearrays which are not correctly "memseted": > bytearray(b'chrome\x00sandbox\x00\x00') > > chrome should be the comm name, but is 'chromesandbox' somehow. See the null > bytes in between. > > Jiri, Arnaldo - I tried to fix this. But the Python binding magic for the > automatically generated events are hard to get comfy. > > Hagen > > PS: assume this fix is also kernel stable relevant. >
patch below fixes it for me, but seems strange this was working till now.. maybe you're the only one using this with python3 ;-)
jirka
--- diff --git a/tools/perf/util/print_binary.c b/tools/perf/util/print_binary.c index 599a1543871d..13fdc51c61d9 100644 --- a/tools/perf/util/print_binary.c +++ b/tools/perf/util/print_binary.c @@ -50,7 +50,7 @@ int is_printable_array(char *p, unsigned int len) len--; - for (i = 0; i < len; i++) { + for (i = 0; i < len && p[i]; i++) { if (!isprint(p[i]) && !isspace(p[i])) return 0; }
| |