[PATCH 2/2] perf tools: Improve EOPNOTSUPP error reporting

[He Zhe <zhe.he@windriver.com>]

There may be multiple reasons for EOPNOTSUPP. Sometimes we cannot determine
which one it is.

For example, when we set up uprobe with 32-bit perf and arm64 kernel on
some hardware that does not support sampling/overflow-interrupts,
$ perf probe -x /lib/libc.so.6 malloc
$ perf record -e probe_libc:malloc -a ls

Before this patch:
probe_libc:malloc: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'

After this patch:
probe_libc:malloc: PMU Hardware may not support sampling/overflow-interrupts. Try 'perf stat'.
Some 64-bit architectures may not support 32-bit instruction probing.

Signed-off-by: He Zhe <zhe.he@windriver.com>
---
 tools/perf/util/evsel.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 1bf76864c4f2..aa56511ddf60 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2697,22 +2697,24 @@ int evsel__open_strerror(struct evsel *evsel, struct target *target,
 		break;
 	case EOPNOTSUPP:
 		if (evsel->core.attr.aux_output)
-			return scnprintf(msg, size,
-	"%s: PMU Hardware doesn't support 'aux_output' feature",
+			printed += scnprintf(msg + printed, size,
+	"%s: PMU Hardware may not support 'aux_output' feature.\n",
 					 evsel__name(evsel));
 		if (evsel->core.attr.sample_period != 0)
-			return scnprintf(msg, size,
-	"%s: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'",
+			printed += scnprintf(msg + printed, size,
+	"%s: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'.\n",
 					 evsel__name(evsel));
 		if (evsel->core.attr.precise_ip)
-			return scnprintf(msg, size, "%s",
-	"\'precise\' request may not be supported. Try removing 'p' modifier.");
+			printed += scnprintf(msg + printed, size, "%s",
+	"\'precise\' request may not be supported. Try removing 'p' modifier.\n");
 #if defined(__i386__) || defined(__x86_64__)
 		if (evsel->core.attr.type == PERF_TYPE_HARDWARE)
-			return scnprintf(msg, size, "%s",
+			printed += scnprintf(msg + printed, size, "%s",
 	"No hardware sampling interrupt available.\n");
 #endif
-		break;
+		scnprintf(msg + printed, size, "%s",
+	"Some 64-bit architectures may not support 32-bit instruction uprobe.\n");
+		return;
 	case EBUSY:
 		if (find_process("oprofiled"))
 			return scnprintf(msg, size,
-- 
2.17.1