1 /*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include <cutils/trace.h>
18 #include <errno.h>
19 #include <fcntl.h>
20 #include <stdio.h>
21 #include <stdlib.h>
22 #include <string.h>
23
24 #include "private/bionic_lock.h"
25 #include "private/bionic_systrace.h"
26 #include "private/libc_logging.h"
27
28 #define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
29 #include <sys/_system_properties.h>
30
31 #define WRITE_OFFSET 32
32
33 constexpr char SYSTRACE_PROPERTY_NAME[] = "debug.atrace.tags.enableflags";
34
35 static Lock g_lock;
36 static const prop_info* g_pinfo;
37 static uint32_t g_property_serial = -1;
38 static uint32_t g_property_area_serial = -1;
39 static uint64_t g_tags;
40 static int g_trace_marker_fd = -1;
41
should_trace()42 static bool should_trace() {
43 bool result = false;
44 g_lock.lock();
45 // debug.atrace.tags.enableflags is set to a safe non-tracing value during property
46 // space initialization, so it should only be null in two cases, if there are
47 // insufficient permissions for this process to access the property, in which
48 // case an audit will be logged, and during boot before the property server has
49 // been started, in which case we store the global property_area serial to prevent
50 // the costly find operation until we see a changed property_area.
51 if (!g_pinfo && g_property_area_serial != __system_property_area_serial()) {
52 g_property_area_serial = __system_property_area_serial();
53 g_pinfo = __system_property_find(SYSTRACE_PROPERTY_NAME);
54 }
55 if (g_pinfo) {
56 // Find out which tags have been enabled on the command line and set
57 // the value of tags accordingly. If the value of the property changes,
58 // the serial will also change, so the costly system_property_read function
59 // can be avoided by calling the much cheaper system_property_serial
60 // first. The values within pinfo may change, but its location is guaranteed
61 // not to move.
62 uint32_t cur_serial = __system_property_serial(g_pinfo);
63 if (cur_serial != g_property_serial) {
64 g_property_serial = cur_serial;
65 char value[PROP_VALUE_MAX];
66 __system_property_read(g_pinfo, 0, value);
67 g_tags = strtoull(value, nullptr, 0);
68 }
69 result = ((g_tags & ATRACE_TAG_BIONIC) != 0);
70 }
71 g_lock.unlock();
72 return result;
73 }
74
get_trace_marker_fd()75 static int get_trace_marker_fd() {
76 g_lock.lock();
77 if (g_trace_marker_fd == -1) {
78 g_trace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_CLOEXEC | O_WRONLY);
79 }
80 g_lock.unlock();
81 return g_trace_marker_fd;
82 }
83
ScopedTrace(const char * message)84 ScopedTrace::ScopedTrace(const char* message) {
85 if (!should_trace()) {
86 return;
87 }
88
89 int trace_marker_fd = get_trace_marker_fd();
90 if (trace_marker_fd == -1) {
91 return;
92 }
93
94 // If bionic tracing has been enabled, then write the message to the
95 // kernel trace_marker.
96 int length = strlen(message);
97 char buf[length + WRITE_OFFSET];
98 size_t len = snprintf(buf, length + WRITE_OFFSET, "B|%d|%s", getpid(), message);
99
100 // Tracing may stop just after checking property and before writing the message.
101 // So the write is acceptable to fail. See b/20666100.
102 TEMP_FAILURE_RETRY(write(trace_marker_fd, buf, len));
103 }
104
~ScopedTrace()105 ScopedTrace::~ScopedTrace() {
106 if (!should_trace()) {
107 return;
108 }
109
110 int trace_marker_fd = get_trace_marker_fd();
111 if (trace_marker_fd == -1) {
112 return;
113 }
114
115 TEMP_FAILURE_RETRY(write(trace_marker_fd, "E", 1));
116 }
117