Messages in this thread Patch in this message | | | Date | Mon, 13 Apr 2015 23:23:12 +0800 | From | He Kuang <> | Subject | Re: [PATCH 1/3] perf probe: Set retprobe flag when probe in address-based alternative mode |
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On 04/13/2015 10:39 PM, Arnaldo Carvalho de Melo wrote: > Em Mon, Apr 13, 2015 at 07:41:28PM +0800, He Kuang escreveu: >> Perf probe misses to set retprobe flag back when falling back to >> address-based alternative mode. > > And when is that happens, can you explain? Because I tried to follow your > instructions, but in my case it worked in the same way before and after your > patch. > > Can you please provide more context for reviewing your patch? >
More details:
[root]# perf probe -v -k vmlinux --add='sys_write%return' probe-definition(0): sys_write%return symbol:sys_write file:(null) line:0 offset:0 return:1 lazy:(null) 0 arguments Use vmlinux: vmlinux map_groups__set_modules_path_dir: cannot open /lib/modules/4.0.0-rc6+ dir Problems setting modules path maps, continuing anyway... Using vmlinux for symbols
Open Debuginfo file: vmlinux >>>==========================
Try to find probe point from debuginfo. Symbol sys_write address found : ffffffff811a8cf0 Probe point found: SyS_write+0 Found 1 probe_trace_events. Opening /sys/kernel/debug/tracing/kprobe_events write=1 Added new event: Writing event: p:probe/sys_write _stext+1739560 probe:sys_write (on sys_write%return)
You can now use it in all perf tools, such as:
perf record -e probe:sys_write -aR sleep 1
[root@buildroot tmp]# cat /sys/kernel/debug/tracing/kprobe_events p:probe/sys_write _stext+1739560
The line I marked is different from your result, which is: """Could not open debuginfo. Try to use symbols."""
When perf probe searched in debuginfo and failed, it tried with alternative, in function get_alternative_probe_event():
memcpy(tmp, &pev->point, sizeof(*tmp)); memset(&pev->point, 0, sizeof(pev->point));
In this case, it drops the retprobe flag and forgets to set it back in find_alternative_probe_point(), so the problem occurred.
> Here are my results: > > Before: > > [root@ssdandy ~]# perf probe -v --add='sys_write%return' > probe-definition(0): sys_write%return > symbol:sys_write file:(null) line:0 offset:0 return:1 lazy:(null) > 0 arguments > Using /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda for symbols > Could not open debuginfo. Try to use symbols. > Opening /sys/kernel/debug/tracing/kprobe_events write=1 > Added new event: > Writing event: r:probe/sys_write sys_write+0 > probe:sys_write (on sys_write%return) > > You can now use it in all perf tools, such as: > > perf record -e probe:sys_write -aR sleep 1 > [root@ssdandy ~]# cat /sys/kernel/debug/tracing/kprobe_events > r:probe/sys_write sys_write > > Remove it: > > [root@ssdandy ~]# perf probe --del *:* > Removed event: probe:sys_write > > After: > > [root@ssdandy ~]# perf probe -v --add='sys_write%return' > probe-definition(0): sys_write%return > symbol:sys_write file:(null) line:0 offset:0 return:1 lazy:(null) > 0 arguments > Using /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda for symbols > Could not open debuginfo. Try to use symbols. > Opening /sys/kernel/debug/tracing/kprobe_events write=1 > Added new event: > Writing event: r:probe/sys_write sys_write+0 > probe:sys_write (on sys_write%return) > > You can now use it in all perf tools, such as: > > perf record -e probe:sys_write -aR sleep 1 > > [root@ssdandy ~]# > [root@ssdandy ~]# cat /sys/kernel/debug/tracing/kprobe_events > r:probe/sys_write sys_write > > Humm, noticed one other problem, but not with your patch, about this message: > > "Could not open debuginfo. Try to use symbols." > > That is really not clear, specially that "try to use symbols" :-) > > [root@ssdandy ~]# ls -la /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda > lrwxrwxrwx. 1 root root 86 Apr 10 18:02 /root/.debug/.build-id/dd/32e51921ede0fd46f034091b7f6a0f2e01ebda -> ../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda > [root@ssdandy ~]# ls -la /root/.debug/.build-id/dd/../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda > -rwxr-xr-x. 1 root root 22698661 Apr 10 18:02 /root/.debug/.build-id/dd/../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda > [root@ssdandy ~]# ls -la /root/.debug/.build-id/dd/../../home/acme/git/build/v4.0.0-rc6+/vmlinux/dd32e51921ede0fd46f034091b7f6a0f2e01ebda > > I.e. it managed to read the debuginfo, its just that it has no symbols in it :-) > > Anyway, digression ended. > > - Arnaldo > >> Can be reproduced as following: >> >> $ perf probe -v -k vmlinux --add='sys_write%return' >> ... >> Added new event: >> Writing event: p:probe/sys_write _stext+1584952 >> probe:sys_write (on sys_write%return) >> >> $ cat /sys/kernel/debug/tracing/kprobe_events >> p:probe/sys_write _stext+1584952 >> >> After this patch: >> >> $ perf probe -v -k vmlinux --add='sys_write%return' >> Added new event: >> Writing event: r:probe/sys_write SyS_write+0 >> probe:sys_write (on sys_write%return) >> >> $ cat /sys/kernel/debug/tracing/kprobe_events >> r:probe/sys_write SyS_write >> >> Signed-off-by: He Kuang <hekuang@huawei.com> >> --- >> tools/perf/util/probe-event.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c >> index 30545ce..5483d98 100644 >> --- a/tools/perf/util/probe-event.c >> +++ b/tools/perf/util/probe-event.c >> @@ -332,6 +332,7 @@ static int find_alternative_probe_point(struct debuginfo *dinfo, >> else { >> result->offset += pp->offset; >> result->line += pp->line; >> + result->retprobe = pp->retprobe; >> ret = 0; >> } >> >> -- >> 2.3.3.220.g9ab698f > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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