A common way to detect an EOF is to perform a read syscall until the return value (the count of the number of bytes to read) is 0. When this happens, programs know that the end-of-file has been reached and will stop calling the read() syscall.
We believe that the op-program when compiled to MIPS will instead read the first 8 bytes of the preimage to determine the length and then perform the exact number of read syscalls to obtain the correct number of bytes from the preimage data. But because we dont actually know how it will be compiled, we are submitting this just in case it actually does the former.
If the MIPS program uses the former method to read the preimage data, the read syscall will revert because the part offset will be out of bounds and therefore cannot be inserted into the preimage oracle. Thus, this line will always revert because the _offset cannot be inserted into the preimage oracle because of OOB error.
For instance, consider a preimage of length 100 (92 bytes of data and 8 bytes to store the length). To read the entire preimage you will need 25 syscalls to read the entire preimage, and 1 syscall to detect the EOF by returning 0.
The MIPS read syscall that returns 0 will have a _partOffset of 100, but this cant be inserted into the preimage oracle because in many of the functions, OOB error will occur because the _partOffset will be 100 which will equal to size + 8 which is 100 and the function will revert.
