Messages in this thread | | | From | Namhyung Kim <> | Subject | [PATCH 0/3] Handle chroot tasks properly (v1) | Date | Fri, 28 Jan 2022 12:39:47 -0800 |
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Hello,
I found that perf tools don't work well with tasks in a chroot. The filenames in MMAP record are from the root directory of the task so it's different than what it sees from outside.
I've tested it with a simple program (myprog - statically built) which just consumes cpu cycles in a loop for a while (default 1 sec, can by overridden by a command-line argument).
# cd $HOME # mkdir -p myroot/bin # cp myprog myroot/bin
# perf record chroot myroot myprog # perf report -D | grep MMAP | grep myprog 2084916774977911 0xa2e4 [0x70]: PERF_RECORD_MMAP2 3363818/3363818: \ [0x401000(0x80000) @ 0x1000 fe:01 4346398 2543719070]: r-xp /bin/myprog
So it's reported as /bin/myprog and then it's unable to symbolize the samples. It seems hard to fix it for the above use case as the record ended after the task exited. It cannot know the root directory of the task anymore. But we can fix it for real-time use cases like perf top or pipe-mode at least.
I tested it again with the following command.
# perf record -o- chroot myroot myprog | perf report -i- ... # # Overhead Command Shared Object Symbol # ........ ....... ................. ................................ # 46.02% myprog myprog [.] 0x000000000000178a 36.71% myprog myprog [.] 0x0000000000001792 17.12% myprog myprog [.] 0x000000000000178e 0.05% myprog myprog [.] 0x0000000000001796 0.05% chroot ld-2.33.so [.] intel_check_word.constprop.0
The symbols are not resolved because it failed to load the symbol table as it didn't find the file in the given path.
So I modified the code to try a new name prepended with the task's root directory when it's not "/". With this change, I can see the symbols of myprog. In fact, it depends on timing if perf report hits the file before the task is gone. Increasing the loop time to 3 sec helped it to get symbols reliably.
# perf record -o- chroot myroot myprog 3 | perf report -i- ... # # Overhead Command Shared Object Symbol # ........ ....... ................. ............................. # 99.83% myprog myprog [.] loop 0.04% chroot [kernel.kallsyms] [k] fxregs_fixup 0.04% chroot [kernel.kallsyms] [k] rsm_load_seg_32 0.03% chroot [kernel.kallsyms] [k] show_cpuinfo_cur_freq 0.01% myprog [kernel.kallsyms] [k] alarmtimer_fired
I also found that perf inject and perf annotate need the similar changes.
You can get it from 'perf/dso-chroot-v1' branch at
git://git.kernel.org/pub/scm/linux/kernel/git/namhyung/linux-perf.git
Thanks, Namhyung
Namhyung Kim (3): perf tools: Try chroot'ed filename when opening dso/symbol perf inject: Try chroot directory when reading build-id perf annotate: Try chroot filename for objdump
tools/perf/builtin-inject.c | 10 ++++++++++ tools/perf/util/annotate.c | 11 +++++++++++ tools/perf/util/dso.c | 15 +++++++++++++-- tools/perf/util/dsos.c | 13 +++++++++++++ tools/perf/util/symbol.c | 10 ++++++++++ tools/perf/util/util.c | 31 +++++++++++++++++++++++++++++++ tools/perf/util/util.h | 2 ++ 7 files changed, 90 insertions(+), 2 deletions(-)
base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07 -- 2.35.0.rc2.247.g8bbb082509-goog
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