RE: [PATCH v2 2/4] perf probe: Fix list result when address is zero

[åæéå / HIRAMATUïMASAMI]

> From: Wangnan (F) [mailto:wangnan0@xxxxxxxxxx]
> >>
> >> When manually added uprobe point with zero address, 'perf probe -l'
> >> reports error. For example:
> >>
> >>   # echo p:probe_libc/abs_0 /path/to/lib.bin:0x0 arg1=%ax > \
> >>             /sys/kernel/debug/tracing/uprobe_events
> >>
> >>   # perf probe -l
> >>   Error: Failed to show event list.
> >>
> >> Probing at 0x0 is possible and useful when lib.bin is not a normal
> >> shared object but is manually mapped. However, in this case kernel
> >> report:
> >>
> >>   # cat /sys/kernel/debug/tracing/uprobe_events
> >>   p:probe_libc/abs_0 /tmp/oxygen_root/lib64/libc-2.18.so:0x          (null) arg1=%ax
> >>
> >> This patch supports the above kernel output.
> > Former part is OK to me.
> >
> >> In addition, this patch also fixes convert_to_perf_probe_point() that,
> >> if failed to find probe point from both of dwarf and map, in all cases
> >> pp->function should be filled with a strdup() result, or the following
> >> ENOMEM error code is incorrect. Remove !tp->module && !is_kprobe
> >> condition so always use address to build function name if symbol is not
> >> found.
> > No, I think this should be included in 3/4, since until that perf probe
> > doesn't support absolute address on kernel.
> 
> This is for manually introduced probing points.
> 
> convert_to_perf_probe_point is called by:
> 
> perf probe -l -> show_perf_probe_events -> __show_perf_probe_events --> convert_to_perf_probe_event
> 
> If there is a manually inserted probing point there, 'perf probe -l' reports an error.
> 
> Here is the result if I remove the second part:
> 
> $ git log --oneline  # I'm in 2/4
> aae2c2c perf probe: Fix list result when address is zero
> 931dff5 perf probe: Prevent segfault when reading probe point with
> absolute address
> ...
> 
> $ git diff    # remove the second part
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 926bcec..de2c27e 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1888,7 +1888,7 @@ static int convert_to_perf_probe_point(struct
> probe_trace_point *tp,
>          if (tp->symbol) {
>                  pp->function = strdup(tp->symbol);
>                  pp->offset = tp->offset;
> -       } else {
> +       } else if (!tp->module && !is_kprobe) {
>                  ret = e_snprintf(buf, 128, "0x%" PRIx64, (u64)tp->address);
>                  if (ret < 0)
>                          return ret;
> 
> 
> ...
> # echo 'p:probe_libc/abs_5 /lib64/libc.so.6:0x5' >
> /sys/kernel/debug/tracing/uprobe_events
> # cat /sys/kernel/debug/tracing/uprobe_events
>   p:probe_libc/abs_5 /lib64/libc.so.6:0x0000000000000005
> # perf probe -l
>    Error: Failed to show event list
> 
> Then add it back:
> 
> $ git reset --hard HEAD
> ...
> # perf probe -l
>   probe_libc:abs_5     (on 0x5 in /lib64/libc.so.6)

Hmm, OK, then this should be in the 1/4 or splitted as an independent patch,
because this part it is not "when address is zero", just support showing
absolute address probes on user applications.

Thank you,