1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 //
15 // Thread-safe logging routines that do not allocate any memory or
16 // acquire any locks, and can therefore be used by low-level memory
17 // allocation, synchronization, and signal-handling code.
18
19 #ifndef ABSL_BASE_INTERNAL_RAW_LOGGING_H_
20 #define ABSL_BASE_INTERNAL_RAW_LOGGING_H_
21
22 #include <string>
23
24 #include "absl/base/attributes.h"
25 #include "absl/base/config.h"
26 #include "absl/base/internal/atomic_hook.h"
27 #include "absl/base/log_severity.h"
28 #include "absl/base/macros.h"
29 #include "absl/base/optimization.h"
30 #include "absl/base/port.h"
31
32 // This is similar to LOG(severity) << format..., but
33 // * it is to be used ONLY by low-level modules that can't use normal LOG()
34 // * it is designed to be a low-level logger that does not allocate any
35 // memory and does not need any locks, hence:
36 // * it logs straight and ONLY to STDERR w/o buffering
37 // * it uses an explicit printf-format and arguments list
38 // * it will silently chop off really long message strings
39 // Usage example:
40 // ABSL_RAW_LOG(ERROR, "Failed foo with %i: %s", status, error);
41 // This will print an almost standard log line like this to stderr only:
42 // E0821 211317 file.cc:123] RAW: Failed foo with 22: bad_file
43
44 #define ABSL_RAW_LOG(severity, ...) \
45 do { \
46 constexpr const char* absl_raw_logging_internal_basename = \
47 ::absl::raw_logging_internal::Basename(__FILE__, \
48 sizeof(__FILE__) - 1); \
49 ::absl::raw_logging_internal::RawLog(ABSL_RAW_LOGGING_INTERNAL_##severity, \
50 absl_raw_logging_internal_basename, \
51 __LINE__, __VA_ARGS__); \
52 } while (0)
53
54 // Similar to CHECK(condition) << message, but for low-level modules:
55 // we use only ABSL_RAW_LOG that does not allocate memory.
56 // We do not want to provide args list here to encourage this usage:
57 // if (!cond) ABSL_RAW_LOG(FATAL, "foo ...", hard_to_compute_args);
58 // so that the args are not computed when not needed.
59 #define ABSL_RAW_CHECK(condition, message) \
60 do { \
61 if (ABSL_PREDICT_FALSE(!(condition))) { \
62 ABSL_RAW_LOG(FATAL, "Check %s failed: %s", #condition, message); \
63 } \
64 } while (0)
65
66 // ABSL_INTERNAL_LOG and ABSL_INTERNAL_CHECK work like the RAW variants above,
67 // except that if the richer log library is linked into the binary, we dispatch
68 // to that instead. This is potentially useful for internal logging and
69 // assertions, where we are using RAW_LOG neither for its async-signal-safety
70 // nor for its non-allocating nature, but rather because raw logging has very
71 // few other dependencies.
72 //
73 // The API is a subset of the above: each macro only takes two arguments. Use
74 // StrCat if you need to build a richer message.
75 #define ABSL_INTERNAL_LOG(severity, message) \
76 do { \
77 constexpr const char* absl_raw_logging_internal_filename = __FILE__; \
78 ::absl::raw_logging_internal::internal_log_function( \
79 ABSL_RAW_LOGGING_INTERNAL_##severity, \
80 absl_raw_logging_internal_filename, __LINE__, message); \
81 if (ABSL_RAW_LOGGING_INTERNAL_##severity == ::absl::LogSeverity::kFatal) \
82 ABSL_INTERNAL_UNREACHABLE; \
83 } while (0)
84
85 #define ABSL_INTERNAL_CHECK(condition, message) \
86 do { \
87 if (ABSL_PREDICT_FALSE(!(condition))) { \
88 std::string death_message = "Check " #condition " failed: "; \
89 death_message += std::string(message); \
90 ABSL_INTERNAL_LOG(FATAL, death_message); \
91 } \
92 } while (0)
93
94 #define ABSL_RAW_LOGGING_INTERNAL_INFO ::absl::LogSeverity::kInfo
95 #define ABSL_RAW_LOGGING_INTERNAL_WARNING ::absl::LogSeverity::kWarning
96 #define ABSL_RAW_LOGGING_INTERNAL_ERROR ::absl::LogSeverity::kError
97 #define ABSL_RAW_LOGGING_INTERNAL_FATAL ::absl::LogSeverity::kFatal
98 #define ABSL_RAW_LOGGING_INTERNAL_LEVEL(severity) \
99 ::absl::NormalizeLogSeverity(severity)
100
101 namespace absl {
102 ABSL_NAMESPACE_BEGIN
103 namespace raw_logging_internal {
104
105 // Helper function to implement ABSL_RAW_LOG
106 // Logs format... at "severity" level, reporting it
107 // as called from file:line.
108 // This does not allocate memory or acquire locks.
109 void RawLog(absl::LogSeverity severity, const char* file, int line,
110 const char* format, ...) ABSL_PRINTF_ATTRIBUTE(4, 5);
111
112 // Writes the provided buffer directly to stderr, in a safe, low-level manner.
113 //
114 // In POSIX this means calling write(), which is async-signal safe and does
115 // not malloc. If the platform supports the SYS_write syscall, we invoke that
116 // directly to side-step any libc interception.
117 void SafeWriteToStderr(const char *s, size_t len);
118
119 // compile-time function to get the "base" filename, that is, the part of
120 // a filename after the last "/" or "\" path separator. The search starts at
121 // the end of the string; the second parameter is the length of the string.
Basename(const char * fname,int offset)122 constexpr const char* Basename(const char* fname, int offset) {
123 return offset == 0 || fname[offset - 1] == '/' || fname[offset - 1] == '\\'
124 ? fname + offset
125 : Basename(fname, offset - 1);
126 }
127
128 // For testing only.
129 // Returns true if raw logging is fully supported. When it is not
130 // fully supported, no messages will be emitted, but a log at FATAL
131 // severity will cause an abort.
132 //
133 // TODO(gfalcon): Come up with a better name for this method.
134 bool RawLoggingFullySupported();
135
136 // Function type for a raw_logging customization hook for suppressing messages
137 // by severity, and for writing custom prefixes on non-suppressed messages.
138 //
139 // The installed hook is called for every raw log invocation. The message will
140 // be logged to stderr only if the hook returns true. FATAL errors will cause
141 // the process to abort, even if writing to stderr is suppressed. The hook is
142 // also provided with an output buffer, where it can write a custom log message
143 // prefix.
144 //
145 // The raw_logging system does not allocate memory or grab locks. User-provided
146 // hooks must avoid these operations, and must not throw exceptions.
147 //
148 // 'severity' is the severity level of the message being written.
149 // 'file' and 'line' are the file and line number where the ABSL_RAW_LOG macro
150 // was located.
151 // 'buffer' and 'buf_size' are pointers to the buffer and buffer size. If the
152 // hook writes a prefix, it must increment *buffer and decrement *buf_size
153 // accordingly.
154 using LogPrefixHook = bool (*)(absl::LogSeverity severity, const char* file,
155 int line, char** buffer, int* buf_size);
156
157 // Function type for a raw_logging customization hook called to abort a process
158 // when a FATAL message is logged. If the provided AbortHook() returns, the
159 // logging system will call abort().
160 //
161 // 'file' and 'line' are the file and line number where the ABSL_RAW_LOG macro
162 // was located.
163 // The NUL-terminated logged message lives in the buffer between 'buf_start'
164 // and 'buf_end'. 'prefix_end' points to the first non-prefix character of the
165 // buffer (as written by the LogPrefixHook.)
166 using AbortHook = void (*)(const char* file, int line, const char* buf_start,
167 const char* prefix_end, const char* buf_end);
168
169 // Internal logging function for ABSL_INTERNAL_LOG to dispatch to.
170 //
171 // TODO(gfalcon): When string_view no longer depends on base, change this
172 // interface to take its message as a string_view instead.
173 using InternalLogFunction = void (*)(absl::LogSeverity severity,
174 const char* file, int line,
175 const std::string& message);
176
177 ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_DLL extern base_internal::AtomicHook<
178 InternalLogFunction>
179 internal_log_function;
180
181 // Registers hooks of the above types. Only a single hook of each type may be
182 // registered. It is an error to call these functions multiple times with
183 // different input arguments.
184 //
185 // These functions are safe to call at any point during initialization; they do
186 // not block or malloc, and are async-signal safe.
187 void RegisterLogPrefixHook(LogPrefixHook func);
188 void RegisterAbortHook(AbortHook func);
189 void RegisterInternalLogFunction(InternalLogFunction func);
190
191 } // namespace raw_logging_internal
192 ABSL_NAMESPACE_END
193 } // namespace absl
194
195 #endif // ABSL_BASE_INTERNAL_RAW_LOGGING_H_
196