[scudo][standalone] Split logs on Android

[cryptoad]

Summary

The function used to log on Android will cut the message past
a certain amount of characters, which mostly materializes when
dumping the size class map on OOM.

This change splits the log message at newline boundaries.

[hctim]

compiler-rt/lib/scudo/standalone/linux.cpp

187

Is this true? Should we just fallback to async_safe_write_log if we don't see a newline? example,

common.cpp:25 has outputRaw("Scudo ERROR: internal map or unmap failure");, and while that'll still be output as it's less than 1024 characters, feels like the invariant that "if it has more than 1K characters it must have a newline" seems fragile.

[cryptoad]

compiler-rt/lib/scudo/standalone/linux.cpp

187

More than 1024 chars with no newline shouldn't happen, particularly since we mostly want things that are human-understandable in the logs
But I'll just fallback to async_safe_write_log.

[hctim]

LGTM w/ planned changes to fallback.

[cryptoad]

If no newline is found, proceed and log the buffer.

[cryptoad]

Without the spurious s in the comment.

compiler-rt/lib/scudo/standalone/linux.cpp

 
 // Allocation free syslog-like API.
 extern "C" WEAK int async_safe_write_log(int pri, const char *tag,
                                          const char *msg);
 
 void outputRaw(const char *Buffer) {
   if (&async_safe_write_log) {
     constexpr s32 AndroidLogInfo = 4;
+    constexpr uptr MaxLength = 1024U;
+    char LocalBuffer[MaxLength];
+    while (strlen(Buffer) > MaxLength) {
+      uptr P;
+      for (P = MaxLength - 1; P > 0; P--) {
+        if (Buffer[P] == '\n') {
+          memcpy(LocalBuffer, Buffer, P);
+          LocalBuffer[P] = '\0';
+          async_safe_write_log(AndroidLogInfo, "scudo", LocalBuffer);
+          Buffer = &Buffer[P + 1];
+          break;
+        }
+      }
+      // If no newline was found, just log the buffer.
+      if (P == 0)
+        break;
+    }
     async_safe_write_log(AndroidLogInfo, "scudo", Buffer);
   } else {
     write(2, Buffer, strlen(Buffer));
   }
 }
 
 extern "C" WEAK void android_set_abort_message(const char *);
 
 void setAbortMessage(const char *Message) {
   if (&android_set_abort_message)
     android_set_abort_message(Message);
 }
 
 } // namespace scudo
 
 #endif // SCUDO_LINUX