The paper submission for Todd Mortimer's #AsiaBSDcon 2019 talk "Removing #ROP gadgets from #OpenBSD", recommended read for those who weren't able to catch the live stream. 
https://doi.asiabsdcon.org/10.25263/asiabsdcon2019/p01b
Other PDF's are up on the asiabsdcon website as well, included a combined PDF.
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Slides are now up too, which go into the solution for aligned ROP gadget reduction for intentional return instructions, or RETGUARD, in a little bit in-depth discussion than the paper. With some very useful examples to help grok. 
https://www.openbsd.org/papers/asiabsdcon2019-rop-slides.pdf
