Boot ROM Loader - mhightower83/Arduino-ESP8266-misc GitHub Wiki
When the Boot ROM loader loads an eboot.bin with multiple segments, the segment(s) preceding the last segment may need to be align filled to 16 bytes. Otherwise, a message similar to ho 0 tail 12 room 4 will appear in the boot message log.
This can be done through the eboot.ld file. Add something like:
.text : ALIGN(4)
{
...
. = ALIGN (16); /* Ensure 16-byte alignment to keep Boot ROM loader happy with multi-segment eboot */
} >iram1_0_seg :iram1_0_phdr
That said, while this will get rid of messages like ho 0 tail 12 room 4 in the boot message log. It is not clear to me, that it is an issue that needs to be fixed. I cannot find any details on that log message. And, I have found boot message logs posted where it occurs and the boot is considered a success.
In reading through some posts I found some boot message logs that did not have the ho 0 tail 12 room 4 message and each segment was not 16 byte filled. At least for the one, I saw the sum of all the segments together was 16-bytes aligned.
They added a multi-segment boot loader in the Arduino ESP8266 pre 3.0 core, so this does not appear to be an issue or real concern