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_serial = -1;
38 static uint64_t g_tags;
39 static int g_trace_marker_fd = -1;
40
should_trace()41 static bool should_trace() {
42 bool result = false;
43 g_lock.lock();
44 // If g_pinfo is null, this means that systrace hasn't been run and it's safe to
45 // assume that no trace writing will need to take place. However, to avoid running
46 // this costly find check each time, we set it to a non-tracing value so that next
47 // time, it will just check the serial to see if the value has been changed.
48 // this function also deals with the bootup case, during which the call to property
49 // set will fail if the property server hasn't yet started.
50 if (g_pinfo == NULL) {
51 g_pinfo = __system_property_find(SYSTRACE_PROPERTY_NAME);
52 if (g_pinfo == NULL) {
53 __system_property_set(SYSTRACE_PROPERTY_NAME, "0");
54 g_pinfo = __system_property_find(SYSTRACE_PROPERTY_NAME);
55 }
56 }
57 if (g_pinfo != NULL) {
58 // Find out which tags have been enabled on the command line and set
59 // the value of tags accordingly. If the value of the property changes,
60 // the serial will also change, so the costly system_property_read function
61 // can be avoided by calling the much cheaper system_property_serial
62 // first. The values within pinfo may change, but its location is guaranteed
63 // not to move.
64 uint32_t cur_serial = __system_property_serial(g_pinfo);
65 if (cur_serial != g_serial) {
66 g_serial = cur_serial;
67 char value[PROP_VALUE_MAX];
68 __system_property_read(g_pinfo, 0, value);
69 g_tags = strtoull(value, NULL, 0);
70 }
71 result = ((g_tags & ATRACE_TAG_BIONIC) != 0);
72 }
73 g_lock.unlock();
74 return result;
75 }
76
get_trace_marker_fd()77 static int get_trace_marker_fd() {
78 g_lock.lock();
79 if (g_trace_marker_fd == -1) {
80 g_trace_marker_fd = open("/sys/kernel/debug/tracing/trace_marker", O_CLOEXEC | O_WRONLY);
81 }
82 g_lock.unlock();
83 return g_trace_marker_fd;
84 }
85
ScopedTrace(const char * message)86 ScopedTrace::ScopedTrace(const char* message) {
87 if (!should_trace()) {
88 return;
89 }
90
91 int trace_marker_fd = get_trace_marker_fd();
92 if (trace_marker_fd == -1) {
93 return;
94 }
95
96 // If bionic tracing has been enabled, then write the message to the
97 // kernel trace_marker.
98 int length = strlen(message);
99 char buf[length + WRITE_OFFSET];
100 size_t len = snprintf(buf, length + WRITE_OFFSET, "B|%d|%s", getpid(), message);
101
102 // Tracing may stop just after checking property and before writing the message.
103 // So the write is acceptable to fail. See b/20666100.
104 TEMP_FAILURE_RETRY(write(trace_marker_fd, buf, len));
105 }
106
~ScopedTrace()107 ScopedTrace::~ScopedTrace() {
108 if (!should_trace()) {
109 return;
110 }
111
112 int trace_marker_fd = get_trace_marker_fd();
113 if (trace_marker_fd == -1) {
114 return;
115 }
116
117 TEMP_FAILURE_RETRY(write(trace_marker_fd, "E", 1));
118 }
119