[PATCH v4 3/3] perf probe: Show better error message when failed to find variable

[He Kuang <hekuang@huawei.com>]

Indicate to check variable location range in error message when we got
failed to find the variable, and put user-supplied variable name in
quotes.

Before this patch:

  $ perf probe --add 'generic_perform_write+118 bytes'
  Failed to find the location of bytes at this address.
   Perhaps, it has been optimized out.
    Error: Failed to add events.

After this patch:
  $ perf probe --add 'generic_perform_write+118 bytes'
  Failed to find the location of the 'bytes' variable at this address.
   Perhaps, it has been optimized out.
   Use -V with --range option to show variable location range.
    Error: Failed to add events.

Signed-off-by: He Kuang <hekuang@huawei.com>
---
 tools/perf/util/probe-finder.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index f032329..0fc2ae8 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -528,8 +528,10 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
 	ret = convert_variable_location(vr_die, pf->addr, pf->fb_ops,
 					&pf->sp_die, pf->tvar);
 	if (ret == -ENOENT || ret == -EINVAL)
-		pr_err("Failed to find the location of %s at this address.\n"
-		       " Perhaps, it has been optimized out.\n", pf->pvar->var);
+		pr_err("Failed to find the location of the '%s' variable at this address.\n"
+		       " Perhaps, it has been optimized out.\n"
+		       " Use -V with --range option to show variable location range.\n",
+		       pf->pvar->var);
 	else if (ret == -ENOTSUP)
 		pr_err("Sorry, we don't support this variable location yet.\n");
 	else if (ret == 0 && pf->pvar->field) {
-- 
1.8.5.2