How can I allocate a variable to a specific section?

There is something else. With your

int rawVideo __attribute__ ((section (".onchip_ram_100Kbytes.rwdata"))); 

line, you are only allocating an integer, which is 4 bytes. This means that each time you do a read of more than 4 bytes, you overwrite a part of memory that could be used for something else, causing random crashes. You need to allocate a buffer big enough for what you want to do. Something like:

char rawVideo __attribute__ ((section (".onchip_ram_100Kbytes.rwdata"))); 

and then remove the & in front of rawVideo in the read call.