[microdump] Move microdump writes to the crash ring-buffer log

src/client/linux/log/log.cc

Index: src/client/linux/log/log.cc
diff --git a/src/client/linux/log/log.cc b/src/client/linux/log/log.cc
index 186359139054177f85239d4a1e94304042c5fcbf..fc23aa6d528a57f067a4748d44ae881224f04ad5 100644
--- a/src/client/linux/log/log.cc
+++ b/src/client/linux/log/log.cc
@@ -31,15 +31,51 @@
 
 #if defined(__ANDROID__)
 #include <android/log.h>
+#include <dlfcn.h>
 #else
 #include "third_party/lss/linux_syscall_support.h"
 #endif
 
 namespace logger {
 
+#if defined(__ANDROID__)
+namespace {
+
+// __android_log_buf_write() is not exported in the NDK and is being used by
+// dynamic runtime linking. Its declaration is taken from Android's
+// system/core/include/log/log.h.
+using AndroidLogBufferWriteFunc = int (*)(int bufID, int prio, const char *tag,
+                                          const char *text);
+const int kAndroidCrashLogId = 4;  // From LOG_ID_CRASH in log.h.
+const char kAndroidLogTag[] = "google-breakpad";
+
+bool g_crash_log_initialized = false;
+AndroidLogBufferWriteFunc g_android_log_buf_write = nullptr;
+
+}  // namespace
+
+void initializeCrashLogWriter() {
+  if (g_crash_log_initialized)
+    return;
+  g_android_log_buf_write = reinterpret_cast<AndroidLogBufferWriteFunc>(
+      dlsym(RTLD_DEFAULT, "__android_log_buf_write"));
+  g_crash_log_initialized = true;
+}
+
+int writeToCrashLog(const char* buf) {
+  // Try writing to the crash log ring buffer. If not available, fall back to
+  // the standard log buffer.
+  if (g_android_log_buf_write) {
+    return g_android_log_buf_write(kAndroidCrashLogId, ANDROID_LOG_FATAL,
+                                   kAndroidLogTag, buf);
+  }
+  return __android_log_write(ANDROID_LOG_FATAL, kAndroidLogTag, buf);
+}
+#endif
+
 int write(const char* buf, size_t nbytes) {
 #if defined(__ANDROID__)
-  return __android_log_write(ANDROID_LOG_WARN, "google-breakpad", buf);
+  return __android_log_write(ANDROID_LOG_WARN, kAndroidLogTag, buf);
 #else
   return sys_write(2, buf, nbytes);
 #endif