[PATCH 02/35] perf probe: Clarify error message about not finding kernel modules debuginfo

From: Arnaldo Carvalho de Melo
Date: Thu Mar 07 2019 - 12:44:59 EST


From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

'perf probe' supports using just the kernel module name, but that will
work only when the module is loaded, or using the full pathname to the
file with the DWARF debug info, but the warning was cryptic:

Before:

# perf probe -m cls_flower -L fl_change
Failed to find the path for cls_flower: No such file or directory
Error: Failed to show lines.
#

After:

# perf probe -m cls_flower -L fl_change
Module cls_flower is not loaded, please specify its full path name.
Error: Failed to show lines.
# perf probe -m /lib/modules/5.0.0-rc7+/kernel/net/sched/cls_flower.ko -L fl_change | head -7
<fl_change@/home/acme/git/linux/net/sched/cls_flower.c:0>
0 static int fl_change(struct net *net, struct sk_buff *in_skb,
struct tcf_proto *tp, unsigned long base,
u32 handle, struct nlattr **tca,
void **arg, bool ovr, struct netlink_ext_ack *extack)
4 {
5 struct cls_fl_head *head = rtnl_dereference(tp->root);
#

The behaviour doesn't change when the module is loaded:

# modprobe cls_flower
# perf probe -m cls_flower -L fl_change | head -7
<fl_change@/home/acme/git/linux/net/sched/cls_flower.c:0>
0 static int fl_change(struct net *net, struct sk_buff *in_skb,
struct tcf_proto *tp, unsigned long base,
u32 handle, struct nlattr **tca,
void **arg, bool ovr, struct netlink_ext_ack *extack)
4 {
5 struct cls_fl_head *head = rtnl_dereference(tp->root);
#

Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Marcelo Ricardo Leitner <mleitner@xxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Link: https://lkml.kernel.org/n/tip-q4njvk9mshra00jacqjbzfn5@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
tools/perf/util/probe-event.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 0030f9b9bf7e..a1b8d9649ca7 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -472,9 +472,12 @@ static struct debuginfo *open_debuginfo(const char *module, struct nsinfo *nsi,
strcpy(reason, "(unknown)");
} else
dso__strerror_load(dso, reason, STRERR_BUFSIZE);
- if (!silent)
- pr_err("Failed to find the path for %s: %s\n",
- module ?: "kernel", reason);
+ if (!silent) {
+ if (module)
+ pr_err("Module %s is not loaded, please specify its full path name.\n", module);
+ else
+ pr_err("Failed to find the path for the kernel: %s\n", reason);
+ }
return NULL;
}
path = dso->long_name;
--
2.20.1