Messages in this thread Patch in this message | | | From | Thomas Richter <> | Subject | [PATCH] trace/uprobes: fix output issue with address randomization | Date | Fri, 15 Dec 2017 16:36:25 +0100 |
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Commit ad67b74d2469 ("printk: hash addresses printed with %p") changed %p to hash pointers in order to avoid leaking kernel addresses.
This breaks the tool perf probe.
To set a uprobe on a function named inet_pton in libc library, 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
However the output shows a randomized address: # cat /sys/kernel/debug/tracing/uprobe_events p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x000000002d0f8952
The displayed address 0x000000002d0f8952 is incorrect and breaks tools post processing it:
# 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)
Using the %px printk format string fixes this issue for root and shows the correct address allowing the perf probe tool to resolve the address to the symbol:
# echo "p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x142060" > /sys/kernel/debug/tracing/uprobe_events # cat /sys/kernel/debug/tracing/uprobe_events p:probe_libc/inet_pton /usr/lib64/libc-2.26.so:0x0000000000142060 # linux/tools/perf/perf probe -l probe_libc:inet_pton (on __inet_pton@resolv/inet_pton.c in /usr/lib64/libc-2.26.so)
Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> --- kernel/trace/trace_uprobe.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index 40592e7b3568..268029ae1be6 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -608,7 +608,7 @@ static int probes_seq_show(struct seq_file *m, void *v) /* Don't print "0x (null)" when offset is 0 */ if (tu->offset) { - seq_printf(m, "0x%p", (void *)tu->offset); + seq_printf(m, "0x%px", (void *)tu->offset); } else { switch (sizeof(void *)) { case 4: -- 2.13.4
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