[PATCH v2 4/4] perf tools: Improve BPF related error messages output

[Wang Nan]

A series of bpf loader related error code is introduced to help error
delivering. Functions are improved to return those new error code.
Functions which return pointers are adjusted to encode error code into
return value using "ERR_PTR".

bpf_loader_strerror() are introduced to convert those error message to
string. It detected the value of error code and calls libbpf_strerror()
and strerror_r() accordingly, so caller don't need to consider checking
the range of error code. bpf__strerror_head() is updated so existing
strerror functions can support these error code automatically.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/util/bpf-loader.c   | 98 +++++++++++++++++++++++++++++++++++++-----
 tools/perf/util/bpf-loader.h   | 18 ++++++++
 tools/perf/util/parse-events.c |  7 +--
 3 files changed, 110 insertions(+), 13 deletions(-)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 76f07ce..375f254 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -14,6 +14,10 @@
 #include "probe-finder.h" // for MAX_PROBES
 #include "llvm-utils.h"
 
+#if BPF_LOADER_ERRNO__END >= LIBBPF_ERRNO__START
+# error Too many BPF loader error code
+#endif
+
 #define DEFINE_PRINT_FN(name, level) \
 static int libbpf_##name(const char *fmt, ...)	\
 {						\
@@ -53,7 +57,7 @@ struct bpf_object *bpf__prepare_load(const char *filename, bool source)
 
 		err = llvm__compile_bpf(filename, &obj_buf, &obj_buf_sz);
 		if (err)
-			return ERR_PTR(err);
+			return ERR_PTR(-BPF_LOADER_ERRNO__ECOMPILE);
 		obj = bpf_object__open_buffer(obj_buf, obj_buf_sz, filename);
 		free(obj_buf);
 	} else
@@ -113,14 +117,14 @@ config_bpf_program(struct bpf_program *prog)
 	if (err < 0) {
 		pr_debug("bpf: '%s' is not a valid config string\n",
 			 config_str);
-		err = -EINVAL;
+		err = -BPF_LOADER_ERRNO__ECONFIG;
 		goto errout;
 	}
 
 	if (pev->group && strcmp(pev->group, PERF_BPF_PROBE_GROUP)) {
 		pr_debug("bpf: '%s': group for event is set and not '%s'.\n",
 			 config_str, PERF_BPF_PROBE_GROUP);
-		err = -EINVAL;
+		err = -BPF_LOADER_ERRNO__EGROUP;
 		goto errout;
 	} else if (!pev->group)
 		pev->group = strdup(PERF_BPF_PROBE_GROUP);
@@ -132,9 +136,9 @@ config_bpf_program(struct bpf_program *prog)
 	}
 
 	if (!pev->event) {
-		pr_debug("bpf: '%s': event name is missing\n",
+		pr_debug("bpf: '%s': event name is missing. Section name should be 'key=value'\n",
 			 config_str);
-		err = -EINVAL;
+		err = -BPF_LOADER_ERRNO__EEVENTNAME;
 		goto errout;
 	}
 	pr_debug("bpf: config '%s' is ok\n", config_str);
@@ -285,7 +289,7 @@ int bpf__foreach_tev(struct bpf_object *obj,
 				(void **)&priv);
 		if (err || !priv) {
 			pr_debug("bpf: failed to get private field\n");
-			return -EINVAL;
+			return -BPF_LOADER_ERRNO__EINTERNAL;
 		}
 
 		pev = &priv->pev;
@@ -308,13 +312,65 @@ int bpf__foreach_tev(struct bpf_object *obj,
 	return 0;
 }
 
+#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))
+
+struct {
+	int code;
+	const char *msg;
+} bpf_loader_strerror_table[] = {
+	{BPF_LOADER_ERRNO__ECONFIG, "Invalid config string"},
+	{BPF_LOADER_ERRNO__EGROUP, "Invalid group name"},
+	{BPF_LOADER_ERRNO__EEVENTNAME, "No event name found in config string"},
+	{BPF_LOADER_ERRNO__EINTERNAL, "BPF loader internal error"},
+	{BPF_LOADER_ERRNO__ECOMPILE, "Error when compiling BPF scriptlet"},
+};
+
+static int
+bpf_loader_strerror(int err, char *buf, size_t size)
+{
+	unsigned int i;
+
+	if (!buf || !size)
+		return -1;
+
+	err = err > 0 ? err : -err;
+
+	if (err > LIBBPF_ERRNO__START)
+		return libbpf_strerror(err, buf, size);
+
+	if (err < BPF_LOADER_ERRNO__START) {
+		char sbuf[STRERR_BUFSIZE], *msg;
+
+		msg = strerror_r(err, sbuf, sizeof(sbuf));
+		snprintf(buf, size, "%s", msg);
+		buf[size - 1] = '\0';
+		return 0;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(bpf_loader_strerror_table); i++) {
+		if (bpf_loader_strerror_table[i].code == err) {
+			const char *msg;
+
+			msg = bpf_loader_strerror_table[i].msg;
+			snprintf(buf, size, "%s", msg);
+			buf[size - 1] = '\0';
+			return 0;
+		}
+	}
+
+	snprintf(buf, size, "Unknown bpf loader error %d", err);
+	buf[size - 1] = '\0';
+	return -1;
+}
+
 #define bpf__strerror_head(err, buf, size) \
 	char sbuf[STRERR_BUFSIZE], *emsg;\
 	if (!size)\
 		return 0;\
 	if (err < 0)\
 		err = -err;\
-	emsg = strerror_r(err, sbuf, sizeof(sbuf));\
+	bpf_loader_strerror(err, sbuf, sizeof(sbuf));\
+	emsg = sbuf;\
 	switch (err) {\
 	default:\
 		scnprintf(buf, size, "%s", emsg);\
@@ -330,13 +386,34 @@ int bpf__foreach_tev(struct bpf_object *obj,
 	}\
 	buf[size - 1] = '\0';
 
+int bpf__strerror_prepare_load(const char *filename, bool source,
+			       int err, char *buf, size_t size)
+{
+	size_t n;
+	int ret;
+
+	n = snprintf(buf, size, "Failed to load %s%s: ",
+			 filename, source ? " from source" : "");
+	if (n >= size) {
+		buf[size - 1] = '\0';
+		return 0;
+	}
+	buf += n;
+	size -= n;
+
+	ret = bpf_loader_strerror(err, buf, size);
+	buf[size - 1] = '\0';
+	return ret;
+}
+
 int bpf__strerror_probe(struct bpf_object *obj __maybe_unused,
 			int err, char *buf, size_t size)
 {
 	bpf__strerror_head(err, buf, size);
 	bpf__strerror_entry(EEXIST, "Probe point exist. Try use 'perf probe -d \"*\"'");
-	bpf__strerror_entry(EPERM, "You need to be root, and /proc/sys/kernel/kptr_restrict should be 0\n");
-	bpf__strerror_entry(ENOENT, "You need to check probing points in BPF file\n");
+	bpf__strerror_entry(EACCES, "You need to be root");
+	bpf__strerror_entry(EPERM, "You need to be root, and /proc/sys/kernel/kptr_restrict should be 0");
+	bpf__strerror_entry(ENOENT, "You need to check probing points in BPF file");
 	bpf__strerror_end(buf, size);
 	return 0;
 }
@@ -345,7 +422,8 @@ int bpf__strerror_load(struct bpf_object *obj __maybe_unused,
 		       int err, char *buf, size_t size)
 {
 	bpf__strerror_head(err, buf, size);
-	bpf__strerror_entry(EINVAL, "%s: Are you root and runing a CONFIG_BPF_SYSCALL kernel?",
+	bpf__strerror_entry(LIBBPF_ERRNO__ELOAD,
+			    "%s: Validate your program and check 'license'/'version' sections in your object",
 			    emsg)
 	bpf__strerror_end(buf, size);
 	return 0;
diff --git a/tools/perf/util/bpf-loader.h b/tools/perf/util/bpf-loader.h
index ccd8d7f..490c78c 100644
--- a/tools/perf/util/bpf-loader.h
+++ b/tools/perf/util/bpf-loader.h
@@ -11,6 +11,14 @@
 #include "probe-event.h"
 #include "debug.h"
 
+#define BPF_LOADER_ERRNO__START		3900
+#define BPF_LOADER_ERRNO__ECONFIG 	3900 /* Invalid config string */
+#define BPF_LOADER_ERRNO__EGROUP 	3901 /* Invalid group name */
+#define BPF_LOADER_ERRNO__EEVENTNAME	3902 /* Event name is missing */
+#define BPF_LOADER_ERRNO__EINTERNAL	3903 /* BPF loader internal error */
+#define BPF_LOADER_ERRNO__ECOMPILE	3904 /* Error when compiling BPF scriptlet */
+#define BPF_LOADER_ERRNO__END		3905
+
 struct bpf_object;
 #define PERF_BPF_PROBE_GROUP "perf_bpf_probe"
 
@@ -19,6 +27,8 @@ typedef int (*bpf_prog_iter_callback_t)(struct probe_trace_event *tev,
 
 #ifdef HAVE_LIBBPF_SUPPORT
 struct bpf_object *bpf__prepare_load(const char *filename, bool source);
+int bpf__strerror_prepare_load(const char *filename, bool source,
+			       int err, char *buf, size_t size);
 
 void bpf__clear(void);
 
@@ -67,6 +77,14 @@ __bpf_strerror(char *buf, size_t size)
 	return 0;
 }
 
+int bpf__strerror_prepare_load(const char *filename __maybe_unused,
+			       bool source __maybe_unused,
+			       int err __maybe_unused,
+			       char *buf, size_t size)
+{
+	return __bpf_strerror(buf, size);
+}
+
 static inline int
 bpf__strerror_probe(struct bpf_object *obj __maybe_unused,
 		    int err __maybe_unused,
diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index c75b25d..e48d9da 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -642,9 +642,10 @@ int parse_events_load_bpf(struct parse_events_evlist *data,
 			snprintf(errbuf, sizeof(errbuf),
 				 "BPF support is not compiled");
 		else
-			snprintf(errbuf, sizeof(errbuf),
-				 "BPF object file '%s' is invalid",
-				 bpf_file_name);
+			bpf__strerror_prepare_load(bpf_file_name,
+						   source,
+						   -err, errbuf,
+						   sizeof(errbuf));
 
 		data->error->help = strdup("(add -v to see detail)");
 		data->error->str = strdup(errbuf);
-- 
1.8.3.4

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