[PATCH v2 2/4] perf probe: Fix list result when address is zero

[Wang Nan <wangnan0@huawei.com>]

When manually added uprobe point with zero address, 'perf probe -l'
reports error. For example:

 # echo p:probe_libc/abs_0 /path/to/lib.bin:0x0 arg1=%ax > \
           /sys/kernel/debug/tracing/uprobe_events

 # perf probe -l
 Error: Failed to show event list.

Probing at 0x0 is possible and useful when lib.bin is not a normal
shared object but is manually mapped. However, in this case kernel
report:

 # cat /sys/kernel/debug/tracing/uprobe_events
 p:probe_libc/abs_0 /tmp/oxygen_root/lib64/libc-2.18.so:0x          (null) arg1=%ax

This patch supports the above kernel output.

In addition, this patch also fixes convert_to_perf_probe_point() that,
if failed to find probe point from both of dwarf and map, in all cases
pp->function should be filled with a strdup() result, or the following
ENOMEM error code is incorrect. Remove !tp->module && !is_kprobe
condition so always use address to build function name if symbol is not
found.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 tools/perf/util/probe-event.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index ef325a2..3ce223d 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1521,9 +1521,31 @@ int parse_probe_trace_command(const char *cmd, struct probe_trace_event *tev)
 	} else
 		p = argv[1];
 	fmt1_str = strtok_r(p, "+", &fmt);
-	if (fmt1_str[0] == '0')	/* only the address started with 0x */
-		tp->address = strtoul(fmt1_str, NULL, 0);
-	else {
+	/* only the address started with 0x */
+	if (fmt1_str[0] == '0')	{
+		/*
+		 * Fix a special case:
+		 * if address == 0, kernel reports something like:
+		 * p:probe_libc/abs_0 /lib/libc-2.18.so:0x          (null) arg1=%ax
+		 * Newer kernel may fix that, but we want to
+		 * support old kernel also.
+		 */
+		if (strcmp(fmt1_str, "0x") == 0) {
+			if (!argv[2] || strcmp(argv[2], "(null)")) {
+				ret = -EINVAL;
+				goto out;
+			}
+			tp->address = 0;
+
+			free(argv[2]);
+			for (i = 2; argv[i + 1] != NULL; i++)
+				argv[i] = argv[i + 1];
+
+			argv[i] = NULL;
+			argc -= 1;
+		} else
+			tp->address = strtoul(fmt1_str, NULL, 0);
+	} else {
 		/* Only the symbol-based probe has offset */
 		tp->symbol = strdup(fmt1_str);
 		if (tp->symbol == NULL) {
@@ -1868,7 +1890,7 @@ static int convert_to_perf_probe_point(struct probe_trace_point *tp,
 	if (tp->symbol) {
 		pp->function = strdup(tp->symbol);
 		pp->offset = tp->offset;
-	} else if (!tp->module && !is_kprobe) {
+	} else {
 		ret = e_snprintf(buf, 128, "0x%" PRIx64, (u64)tp->address);
 		if (ret < 0)
 			return ret;
-- 
1.8.3.4