Initial Commit

absl/base/internal/raw_logging.cc

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+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <atomic>
+#include <cassert>
+#include <cstdarg>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/atomic_hook.h"
+#include "absl/base/internal/log_severity.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/port.h"
+
+// We know how to perform low-level writes to stderr in POSIX and Windows.  For
+// these platforms, we define the token ABSL_LOW_LEVEL_WRITE_SUPPORTED.
+// Much of raw_logging.cc becomes a no-op when we can't output messages,
+// although a FATAL ABSL_RAW_LOG message will still abort the process.
+
+// ABSL_HAVE_POSIX_WRITE is defined when the platform provides posix write()
+// (as from unistd.h)
+//
+// This preprocessor token is also defined in raw_io.cc.  If you need to copy
+// this, consider moving both to config.h instead.
+#if defined(__linux__) || defined(__APPLE__) || defined(__Fuchsia__) || \
+    defined(__GENCLAVE__)
+#include <unistd.h>
+#define ABSL_HAVE_POSIX_WRITE 1
+#define ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
+#else
+#undef ABSL_HAVE_POSIX_WRITE
+#endif
+
+// ABSL_HAVE_SYSCALL_WRITE is defined when the platform provides the syscall
+//   syscall(SYS_write, /*int*/ fd, /*char* */ buf, /*size_t*/ len);
+// for low level operations that want to avoid libc.
+#if defined(__linux__) && !defined(__ANDROID__)
+#include <sys/syscall.h>
+#define ABSL_HAVE_SYSCALL_WRITE 1
+#define ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
+#else
+#undef ABSL_HAVE_SYSCALL_WRITE
+#endif
+
+#ifdef _WIN32
+#include <io.h>
+#define ABSL_HAVE_RAW_IO 1
+#define ABSL_LOW_LEVEL_WRITE_SUPPORTED 1
+#else
+#undef ABSL_HAVE_RAW_IO
+#endif
+
+// TODO(gfalcon): We want raw-logging to work on as many platforms as possible.
+// Explicitly #error out when not ABSL_LOW_LEVEL_WRITE_SUPPORTED, except for a
+// whitelisted set of platforms for which we expect not to be able to raw log.
+
+ABSL_CONST_INIT static absl::base_internal::AtomicHook<
+    absl::raw_logging_internal::LogPrefixHook> log_prefix_hook;
+ABSL_CONST_INIT static absl::base_internal::AtomicHook<
+    absl::raw_logging_internal::AbortHook> abort_hook;
+
+#ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
+static const char kTruncated[] = " ... (message truncated)\n";
+
+// sprintf the format to the buffer, adjusting *buf and *size to reflect the
+// consumed bytes, and return whether the message fit without truncation.  If
+// truncation occurred, if possible leave room in the buffer for the message
+// kTruncated[].
+inline static bool VADoRawLog(char** buf, int* size,
+                              const char* format, va_list ap) {
+  int n = vsnprintf(*buf, *size, format, ap);
+  bool result = true;
+  if (n < 0 || n > *size) {
+    result = false;
+    if (static_cast<size_t>(*size) > sizeof(kTruncated)) {
+      n = *size - sizeof(kTruncated);  // room for truncation message
+    } else {
+      n = 0;                           // no room for truncation message
+    }
+  }
+  *size -= n;
+  *buf += n;
+  return result;
+}
+#endif  // ABSL_LOW_LEVEL_WRITE_SUPPORTED
+
+static constexpr int kLogBufSize = 3000;
+
+namespace absl {
+namespace raw_logging_internal {
+void SafeWriteToStderr(const char *s, size_t len);
+}  // namespace raw_logging_internal
+}  // namespace absl
+
+namespace {
+
+// CAVEAT: vsnprintf called from *DoRawLog below has some (exotic) code paths
+// that invoke malloc() and getenv() that might acquire some locks.
+// If this becomes a problem we should reimplement a subset of vsnprintf
+// that does not need locks and malloc.
+// E.g. google3/third_party/clearsilver/core/util/snprintf.c
+// looks like such a reimplementation.
+
+// Helper for RawLog below.
+// *DoRawLog writes to *buf of *size and move them past the written portion.
+// It returns true iff there was no overflow or error.
+bool DoRawLog(char** buf, int* size, const char* format, ...)
+    ABSL_PRINTF_ATTRIBUTE(3, 4);
+bool DoRawLog(char** buf, int* size, const char* format, ...) {
+  va_list ap;
+  va_start(ap, format);
+  int n = vsnprintf(*buf, *size, format, ap);
+  va_end(ap);
+  if (n < 0 || n > *size) return false;
+  *size -= n;
+  *buf += n;
+  return true;
+}
+
+void RawLogVA(absl::LogSeverity severity, const char* file, int line,
+              const char* format, va_list ap) {
+  char buffer[kLogBufSize];
+  char* buf = buffer;
+  int size = sizeof(buffer);
+#ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
+  bool enabled = true;
+#else
+  bool enabled = false;
+#endif
+
+#ifdef ABSL_MIN_LOG_LEVEL
+  if (static_cast<int>(severity) < ABSL_MIN_LOG_LEVEL &&
+      severity < absl::LogSeverity::kFatal) {
+    enabled = false;
+  }
+#endif
+
+  auto log_prefix_hook_ptr = log_prefix_hook.Load();
+  if (log_prefix_hook_ptr) {
+    enabled = log_prefix_hook_ptr(severity, file, line, &buf, &size);
+  } else {
+    if (enabled) {
+      DoRawLog(&buf, &size, "[%s : %d] RAW: ", file, line);
+    }
+  }
+  const char* const prefix_end = buf;
+
+#ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
+  if (enabled) {
+    bool no_chop = VADoRawLog(&buf, &size, format, ap);
+    if (no_chop) {
+      DoRawLog(&buf, &size, "\n");
+    } else {
+      DoRawLog(&buf, &size, "%s", kTruncated);
+    }
+    absl::raw_logging_internal::SafeWriteToStderr(buffer, strlen(buffer));
+  }
+#else
+  static_cast<void>(format);
+  static_cast<void>(ap);
+#endif
+
+  // Abort the process after logging a FATAL message, even if the output itself
+  // was suppressed.
+  if (severity == absl::LogSeverity::kFatal) {
+    abort_hook(file, line, buffer, prefix_end, buffer + kLogBufSize);
+    abort();
+  }
+}
+
+}  // namespace
+
+namespace absl {
+namespace raw_logging_internal {
+
+// Writes the provided buffer directly to stderr, in a safe, low-level manner.
+//
+// In POSIX this means calling write(), which is async-signal safe and does
+// not malloc.  If the platform supports the SYS_write syscall, we invoke that
+// directly to side-step any libc interception.
+void SafeWriteToStderr(const char *s, size_t len) {
+#if defined(ABSL_HAVE_SYSCALL_WRITE)
+  syscall(SYS_write, STDERR_FILENO, s, len);
+#elif defined(ABSL_HAVE_POSIX_WRITE)
+  write(STDERR_FILENO, s, len);
+#elif defined(ABSL_HAVE_RAW_IO)
+  _write(/* stderr */ 2, s, len);
+#else
+  // stderr logging unsupported on this platform
+  (void) s;
+  (void) len;
+#endif
+}
+
+void RawLog(absl::LogSeverity severity, const char* file, int line,
+            const char* format, ...) {
+  va_list ap;
+  va_start(ap, format);
+  RawLogVA(severity, file, line, format, ap);
+  va_end(ap);
+}
+
+bool RawLoggingFullySupported() {
+#ifdef ABSL_LOW_LEVEL_WRITE_SUPPORTED
+  return true;
+#else  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
+  return false;
+#endif  // !ABSL_LOW_LEVEL_WRITE_SUPPORTED
+}
+
+}  // namespace raw_logging_internal
+}  // namespace absl