title: how to rebuild bbl with payload option
body: <p>I'm rebuilding fesvr, pk and bbl run applications on a zedboard. fester, pk runs well, but bbl seems to be built with a dummy payload.</p>
  
  <p>Does anyone know how to rebuilt bbl with proper payload? When I boot riscv-linux with "$ fesvr-zedboard +disk=/sdcard/riscv/root.bin bbl /sdcard/riscv/vmlinux", the "R" logo shows up, and then the console puts "bbl is built with dummy payload. Rebuild it using --with-payload= option".</p>
  
  <p>I looked at the payload.S assembly code under riscv-tools/pk/bbl, it seems the building process wants to include a correct program that sets up something. Does anyone know how to write such a payload code file for zed board, or can I find it somewhere?</p>
  
  <p>One more question, I found riscv-poky to be a better linux distribution. Do I need to use the same command, i.e., fesvr xxx bbl yyy to boot riscv-poky? I've read other ppl have encountered trouble in doing this: <a href="https://stackoverflow.com/questions/32737946/how-to-boot-the-linux-of-riscv-poky-on-zedboard">How to boot the linux of riscv-poky on ZedBoard?</a></p>