debuggerd: remove maximum abort message length.

Let the logging implementation be the imposer of limits.

Bug: http://b/64759619
Test: debuggerd_test
Change-Id: I8bc73bf2301ce071668993b740880224846a4e75

debuggerd/debuggerd_test.cpp

@@ -354,7 +354,14 @@ TEST_F(CrasherTest, abort_message) {
   int intercept_result;
   unique_fd output_fd;
   StartProcess([]() {
-    android_set_abort_message("abort message goes here");
+    // Arrived at experimentally;
+    // logd truncates at 4062.
+    // strlen("Abort message: ''") is 17.
+    // That's 4045, but we also want a NUL.
+    char buf[4045 + 1];
+    memset(buf, 'x', sizeof(buf));
+    buf[sizeof(buf) - 1] = '\0';
+    android_set_abort_message(buf);
     abort();
   });
   StartIntercept(&output_fd);
@@ -366,7 +373,7 @@ TEST_F(CrasherTest, abort_message) {
 
   std::string result;
   ConsumeFd(std::move(output_fd), &result);
-  ASSERT_MATCH(result, R"(Abort message: 'abort message goes here')");
+  ASSERT_MATCH(result, R"(Abort message: 'x{4045}')");
 }
 
 TEST_F(CrasherTest, abort_message_backtrace) {

debuggerd/libdebuggerd/tombstone.cpp

@@ -239,19 +239,23 @@ static void dump_abort_message(log_t* log, Memory* process_memory, uint64_t addr
     return;
   }
 
-  char msg[512];
-  if (length >= sizeof(msg)) {
-    _LOG(log, logtype::HEADER, "Abort message too long: claimed length = %zd\n", length);
+  // The length field includes the length of the length field itself.
+  if (length < sizeof(size_t)) {
+    _LOG(log, logtype::HEADER, "Abort message header malformed: claimed length = %zd\n", length);
     return;
   }
 
-  if (!process_memory->ReadFully(address + sizeof(length), msg, length)) {
+  length -= sizeof(size_t);
+
+  std::vector<char> msg(length);
+  if (!process_memory->ReadFully(address + sizeof(length), &msg[0], length)) {
     _LOG(log, logtype::HEADER, "Failed to read abort message: %s\n", strerror(errno));
     return;
   }
 
+  // The abort message should be null terminated already, but just in case...
   msg[length] = '\0';
-  _LOG(log, logtype::HEADER, "Abort message: '%s'\n", msg);
+  _LOG(log, logtype::HEADER, "Abort message: '%s'\n", &msg[0]);
 }
 
 static void dump_all_maps(log_t* log, BacktraceMap* map, Memory* process_memory, uint64_t addr) {

debuggerd/libdebuggerd/utility.cpp

@@ -74,25 +74,22 @@ void _LOG(log_t* log, enum logtype ltype, const char* fmt, ...) {
                       && (log->crashed_tid == log->current_tid);
   static bool write_to_kmsg = should_write_to_kmsg();
 
-  char buf[512];
+  std::string msg;
   va_list ap;
   va_start(ap, fmt);
-  vsnprintf(buf, sizeof(buf), fmt, ap);
+  android::base::StringAppendV(&msg, fmt, ap);
   va_end(ap);
 
-  size_t len = strlen(buf);
-  if (len <= 0) {
-    return;
-  }
+  if (msg.empty()) return;
 
   if (write_to_tombstone) {
-    TEMP_FAILURE_RETRY(write(log->tfd, buf, len));
+    TEMP_FAILURE_RETRY(write(log->tfd, msg.c_str(), msg.size()));
   }
 
   if (write_to_logcat) {
-    __android_log_buf_write(LOG_ID_CRASH, ANDROID_LOG_FATAL, LOG_TAG, buf);
+    __android_log_buf_write(LOG_ID_CRASH, ANDROID_LOG_FATAL, LOG_TAG, msg.c_str());
     if (log->amfd_data != nullptr) {
-      *log->amfd_data += buf;
+      *log->amfd_data += msg;
     }
 
     if (write_to_kmsg) {
@@ -100,11 +97,11 @@ void _LOG(log_t* log, enum logtype ltype, const char* fmt, ...) {
       if (kmsg_fd.get() >= 0) {
         // Our output might contain newlines which would otherwise be handled by the android logger.
         // Split the lines up ourselves before sending to the kernel logger.
-        if (buf[len - 1] == '\n') {
-          buf[len - 1] = '\0';
+        if (msg.back() == '\n') {
+          msg.back() = '\0';
         }
 
-        std::vector<std::string> fragments = android::base::Split(buf, "\n");
+        std::vector<std::string> fragments = android::base::Split(msg, "\n");
         for (const std::string& fragment : fragments) {
           static constexpr char prefix[] = "<3>DEBUG: ";
           struct iovec iov[3];