Re: [PATCH] perf probe: Fix module probing with shortname

Arnaldo Carvalho de Melo
2015-09-23T02:49:09Z

Em Wed, Sep 23, 2015 at 09:14:44AM +0800, Wangnan (F) escreveu:
>
>
> On 2015/9/22 21:35, Arnaldo Carvalho de Melo wrote:
> >Em Tue, Sep 22, 2015 at 03:34:32AM +0000, Wang Nan escreveu:
> >>After commit 3d39ac538629e4f00a6e1c38d46346f1b8e69505 ("perf machine:
> >>No need to have two DSOs lists"), perf probe with module short name doesn't
> >>work again. For example:
> >>
> >> # lsmod | grep e1000e
> >> e1000e 233472 0
> >>
> >> # cat /proc/modules | grep e1000e
> >> e1000e 233472 0 - Live 0xffffffffa0073000
> >>
> >> # cat /proc/kallsyms | grep '\<e1000e_up\>'
> >> ffffffffa0093860 t e1000e_up[e1000e]
> >>
> >> # perf probe -v -m e1000e --add e1000e_up
> >> probe-definition(0): e1000e_up
> >> symbol:e1000e_up file:(null) line:0 offset:0 return:0 lazy:(null)
> >> 0 arguments
> >> Failed to find module e1000e.
> >> Could not open debuginfo. Try to use symbols.
> >> Looking at the vmlinux_path (7 entries long)
> >> Using /lib/modules/4.2.0-rc7+/build/vmlinux for symbols
> >> e1000e_up is out of .text, skip it.
> >> Error: Failed to add events. Reason: No such file or directory (Code: -2)
> >>
> >>This is caused by a misunderstood of dso->kernel in kernel_get_module_dso()
> >>that, for kernel module, dso->kernel is DSO_TYPE_USER. dso->kernel is DSO_TYPE_KERNEL
> >>iff dso is vmlinux.
> >Kernel modules having DSO_TYPE_USER seems to be the bug, no? I'll try to
> >check that...
>
> I also noticed this problem when I working on commit
> 1f121b03d058dd07199d8924373d3c52a207f63b ("perf tools: Deal with
> kernel module names in '[]' correctly") ;)

Thanks for working on this, it is an area that needs cleaning up, too
many ways to say what a dso is, will study your findings and try to come
up with a patch proposal tomorrow.

- Arnaldo

> It should be bug, but I think fixing it is costy. Here's an
> assumption that, if dso->kernel
> is not zero, the dso should be vmlinux (not kernel module):
>
> $ grep 'dso.>kernel)' ./tools/perf/ -r
> ./tools/perf/builtin-inject.c: if (dso->kernel)
> ./tools/perf/util/symbol.c: if (dso->kernel) {
> ./tools/perf/util/symbol-elf.c: if (dso->kernel)
> ./tools/perf/util/symbol-elf.c: if (remap_kernel &&
> dso->kernel) {
> ./tools/perf/util/event.c: if (pos->dso->kernel)
> ./tools/perf/util/probe-event.c: if (dso->kernel)
> ./tools/perf/util/map.c: * map->dso->kernel) before calling
> __map__is_{kernel,kmodule}())
> ./tools/perf/util/map.c: if (!map->dso || !map->dso->kernel) {
> ./tools/perf/builtin-top.c: if (!map->dso->kernel)
>
> So care must be taken.
>
> Another solution seems simpler: we can redefine the meaning of enum
> dso_kernel_type like this:
>
> # find ./tools/perf/ -type f | xargs -n1 sed -i
> 's/DSO_TYPE_USER/DSO_TYPE_NOT_VMLINUX/g'
> # find ./tools/perf/ -type f | xargs -n1 sed -i
> 's/DSO_TYPE_KERNEL/DSO_TYPE_VMLINUX/g'
> # find ./tools/perf/ -type f | xargs -n1 sed -i
> 's/DSO_TYPE_GUEST_KERNEL/DSO_TYPE_GUEST_VMLINUX/g'
>
> By fixing the name of DSO_TYPE_USER, kernel module with
> DSO_TYPE_NOT_VMLINUX seems
> not so buggy. (Please choose a better name...)
>
> What's your opinion?
>
> Thank you.
>
> >- Arnaldo
> >
> >>This patch fix 'perf probe -m' with an ad-hoc way.
> >>
> >>After this patch:
> >>
> >> # perf probe -v -m e1000e --add e1000e_up
> >> probe-definition(0): e1000e_up
> >> symbol:e1000e_up file:(null) line:0 offset:0 return:0 lazy:(null)
> >> 0 arguments
> >> Open Debuginfo file: /lib/modules/4.2.0-rc7+/kernel/drivers/net/ethernet/intel/e1000e/e1000e.ko
> >> Try to find probe point from debuginfo.
> >> Matched function: e1000e_up
> >> Probe point found: e1000e_up+0
> >> Found 1 probe_trace_events.
> >> Opening /sys/kernel/debug/tracing//kprobe_events write=1
> >> Writing event: p:probe/e1000e_up e1000e:e1000e_up+0
> >> Added new event:
> >> probe:e1000e_up (on e1000e_up in e1000e)
> >>
> >> You can now use it in all perf tools, such as:
> >>
> >> perf record -e probe:e1000e_up -aR sleep 1
> >>
> >> # perf probe -l
> >> Failed to find debug information for address ffffffffa0093860
> >> probe:e1000e_up (on e1000e_up in e1000e)
> >>
> >>Signed-off-by: Wang Nan <wangnan0@huawei.com>
> >>Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> >>Cc: Namhyung Kim <namhyung@kernel.org>
> >>Cc: Jiri Olsa <jolsa@redhat.com>
> >>Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> >>---
> >>
> >>I think there may be other places where dso->kernel is misused.
> >>machine__process_kernel_mmap_event() may be one of them. If I understand
> >>correctly, 'dso->kernel && is_kernel_module(dso->long_name)' should always
> >>false theoretically. However, I don't have enough time to check whether that
> >>code really cause problem.
> >>
> >>---
> >> tools/perf/util/probe-event.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >>diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >>index 2b78e8f..c7d6d3d 100644
> >>--- a/tools/perf/util/probe-event.c
> >>+++ b/tools/perf/util/probe-event.c
> >>@@ -270,7 +270,7 @@ static int kernel_get_module_dso(const char *module, struct dso **pdso)
> >> if (module) {
> >> list_for_each_entry(dso, &host_machine->dsos.head, node) {
> >>- if (!dso->kernel)
> >>+ if (dso->kernel)
> >> continue;
> >> if (strncmp(dso->short_name + 1, module,
> >> dso->short_name_len - 2) == 0)
> >>--
> >>1.8.3.4
>