There's several examples of P-code/Pascal VMs around [0][1][2][3]. Some more detailed than others.
[0] https://en.wikipedia.org/wiki/P-code_machine#Example_machine [1] http://www.icodeguru.com/vc/10book/books/book4/secg.htm [2] http://blackmesatech.com/2011/12/pl0/pl0.xhtml [3] https://github.com/lkesteloot/turbopascal On Sat, Jun 18, 2016 at 10:39 AM, Kamil Cholewiński <harry6...@gmail.com> wrote: > On Sat, 18 Jun 2016, Connor Lane Smith <c...@lubutu.com> wrote: >> Hi all, >> >> I was wondering if others had an opinion on JIT. Suppose we don't need >> anything fancy like adaptive optimisation, but just wanted to compile >> a program at runtime. One possibility might be to generate C code and >> store that in a file and then call the C compiler and then execute the >> resulting binary... But that seems a bit unpleasant, prone to >> compilation failure, and not particularly lightweight either. >> >> One solution could be simply to produce assembly code, but then that >> is tied to a specific architecture, which is unfortunate. There's also >> LLVM, but that is a very big and complicated dependency, which >> shouldn't really be necessary if we're just jitting something quickly >> and don't mind it being a little unoptimised for the sake of >> simplicity and speed of compilation. We just want to portably generate >> machine code and then run it. >> >> An ideal might be something like an abstract instruction set together >> with a JIT for the abstract machine. To be honest a JIT might not even >> be necessary so long as it is has very little interpretation overhead, >> the instruction set is general purpose and fixed, and it plays well >> with the C memory model. >> >> Does anyone have any ideas? >> >> Thanks, >> cls > > Hi Connor, > > Creating a simple and general-purpose VM shouldn't be hard! It used to > be my favourite exercise for learning a new programming language. > > Probably much more difficult to get real-world performance; I wouldn't > be surprised if the initial efforts resulted in a 1000x-slower-than-C > execution speed for typical programs. > > With lots of test cases, tuning, benchmarks, and generally a lot of hard > work, I can imagine you could bring it to the 10-100x-slower[1] class. > > [1]: > https://benchmarksgame.alioth.debian.org/u64q/compare.php?lang=python3&lang2=gcc > > Of course this doesn't matter that much if your purpose is mostly > scripting behavior (games), or IO-bound stuff (as in waiting for > database - things like Snabb[2] actually do need some real power). > Having good C interop via FFI can save you in many cases. > > [2]: https://github.com/snabbco/snabb > > Yes, JITing is inherently architecture-specific, but the bytecode can be > designed with trade-offs between interpretation and compilation speed. > These days supporting x86-64, ARM and MIPS probably covers >99% of the > devices you'll ever encounter in the wild; the rest can run a bit slower > until someone is motivated enough to write a JIT backend. > > I've never had a close look at any of the Big Name VMs, as most of that > code must suck horribly. Some real-world VMs&JITs however remained > relatively simple - I think there might be a lot to learn from Dis[3] > and LuaJIT[4]. > > [3]: http://doc.cat-v.org/inferno/4th_edition/dis_VM_design > [4]: http://luajit.org/ > > If you have some concrete applications in mind, please do share. I'd > gladly give a shot at prototyping something in this area. > > <3,K. >