Re: [PATCH] perf-probe: dso: Add symbols in .text.* subsections to text symbol map in kenrel modules

[Evgenii Shatokhin]

On 23.02.2021 23:11, Arnaldo Carvalho de Melo wrote:
> Em Tue, Feb 23, 2021 at 06:02:58PM +0300, Evgenii Shatokhin escreveu:
> > On 23.02.2021 10:37, Masami Hiramatsu wrote:
> > > The kernel modules have .text.* subsections such as .text.unlikely.
> > > Since dso__process_kernel_symbol() only identify the symbols in the ".text"
> > > section as the text symbols and inserts it in the default dso in the map,
> > > the symbols in such subsections can not be found by map__find_symbol().
> > >
> > > This adds the symbols in those subsections to the default dso in the map so
> > > that map__find_symbol() can find them. This solves the perf-probe issue on
> > > probing online module.
> > >
> > > Without this fix, probing on a symbol in .text.unlikely fails.
> > >     ----
> > >     # perf probe -m nf_conntrack nf_l4proto_log_invalid
> > >     Probe point 'nf_l4proto_log_invalid' not found.
> > >       Error: Failed to add events.
> > >     ----
> > >
> > > With this fix, it works because map__find_symbol() can find the symbol
> > > correctly.
> > >     ----
> > >     # perf probe -m nf_conntrack nf_l4proto_log_invalid
> > >     Added new event:
> > >       probe:nf_l4proto_log_invalid (on nf_l4proto_log_invalid in nf_conntrack)
> > >
> > >     You can now use it in all perf tools, such as:
> > >
> > >     	perf record -e probe:nf_l4proto_log_invalid -aR sleep 1
> > >
> > >     ----
> > >
> > > Reported-by: Evgenii Shatokhin <eshatokhin@xxxxxxxxxxxxx>
> > > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> >
> > Thanks for the fix!
> >
> > It looks like it helps, at least with nf_conntrack in kernel 5.11:
>
> So I'm taking this as you providing a:
>
> Tested-by: Evgenii Shatokhin <eshatokhin@xxxxxxxxxxxxx>
>
> ok?

Sure, thanks!

> - Arnaldo
>
> > ---------------------
> > # ./perf probe -v -m nf_conntrack nf_ct_resolve_clash
> > probe-definition(0): nf_ct_resolve_clash
> > symbol:nf_ct_resolve_clash file:(null) line:0 offset:0 return:0 lazy:(null)
> > 0 arguments
> > Failed to get build-id from nf_conntrack.
> > Cache open error: -1
> > Open Debuginfo file:
> > /lib/modules/5.11.0-test01/kernel/net/netfilter/nf_conntrack.ko
> > Try to find probe point from debuginfo.
> > Matched function: nf_ct_resolve_clash [33616]
> > Probe point found: nf_ct_resolve_clash+0
> > Found 1 probe_trace_events.
> > Opening /sys/kernel/tracing//kprobe_events write=1
> > Opening /sys/kernel/tracing//README write=0
> > Writing event: p:probe/nf_ct_resolve_clash
> > nf_conntrack:nf_ct_resolve_clash+0
> > Added new event:
> >    probe:nf_ct_resolve_clash (on nf_ct_resolve_clash in nf_conntrack)
> >
> > You can now use it in all perf tools, such as:
> >
> >          perf record -e probe:nf_ct_resolve_clash -aR sleep 1
> > ---------------------
> >
> > I guess, the patch is suitable for stable kernel branches as well.
> >
> > Without the patch, the workaround you suggested earlier (using the full path
> > to nf_conntrack.ko) works too.
> >
> > > ---
> > >    tools/perf/util/symbol-elf.c |    4 +++-
> > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> > > index 6dff843fd883..0c1113236913 100644
> > > --- a/tools/perf/util/symbol-elf.c
> > > +++ b/tools/perf/util/symbol-elf.c
> > > @@ -985,7 +985,9 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
> > >    	if (strcmp(section_name, (curr_dso->short_name + dso->short_name_len)) == 0)
> > >    		return 0;
> > > -	if (strcmp(section_name, ".text") == 0) {
> > > +	/* .text and .text.* are included in the text dso */
> > > +	if (strncmp(section_name, ".text", 5) == 0 &&
> > > +	    (section_name[5] == '\0' || section_name[5] == '.')) {
> > >    		/*
> > >    		 * The initial kernel mapping is based on
> > >    		 * kallsyms and identity maps.  Overwrite it to
> > >
> > > .
> >
> > Regards,
> > Evgenii