During debugging of perf probe tool I discovered an issue with
uprobes and address randomization.
To set a uprobe on a function named inet_pton in libc library, you
obtain the address of the symbol inet_pton using command nm and
then use the following command to set the uprobe:
# echo "p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x142060"
> /sys/kernel/debug/tracing/uprobe_events
0x142060 is the address of inet_pton on my system.
This works nicely and the uprobe is usable.
The issue is with the output:
# cat /sys/kernel/debug/tracing/uprobe_events
p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x000000002d0f8952
#
The displayed address 0x000000002d0f8952 is wrong, probably
randomized and post processing of this output with the perf
probe tool fails due to this random address:
# linux/tools/perf/perf probe -l
Failed to find debug information for address 2d0f8952
probe_libc:inet_pton (on 0x2d0f8952 in /usr/lib64/libc-2.26.so)
#
So how to fix this (if at all)?
Is replacing %p by %llx in line 612 of file kernel/trace/trace_uprobe.c
seq_printf(m, "0x%p", (void *)tu->offset)
an option?
Or is this broken by design and intention?
Thanks for hints and suggestions.
--
Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany
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