from Hacker News

How does dynamic dispatch work in WebAssembly?

by mnemonik on 4/26/18, 3:46 PM with 19 comments

• by repsilat on 4/28/18, 3:16 AM

  Kinda annoying, but not surprising. VMs and bytecode formats make simplifying assumptions based on the languages they expect to be hosted on top of them, and that usually means "Something with control flow like C."

  Creative uses of computed jumps, messing with the stack, dynamic codegen, all sorts of weird things your new language might do to efficiently implement some new control or data structure aren't likely to be possible.

  At least in the short term nobody is going to be too upset. Today if something needs to wring all the power available from your CPU it isn't reasonable to put it on the web. That will continue to be true. WASM is the wise 80% solution, not a toy for ASM hackers and people messing around with weird prototype programming languages.

• by amluto on 4/27/18, 11:02 PM

  Someone should make a CPU that does this. Intel CET is a bit of a start, but a CALL instruction that takes a “type” operand and only calls functions of that type would be a big improvement. So would a totally separate return address stack.

• by merlish on 4/28/18, 11:32 AM

  How do you implement co-operative multitasking in WebAssembly?

  Do you have to analyze the source program & know where every possible call to a yield is, and store all resulting suffixes of a function as new functions?

• by foota on 4/28/18, 3:24 AM

  I'll be interested to read about the first WASM vulnerabilities that are revealed.

• by gok on 4/28/18, 1:46 AM

  So how are function pointers in (say) C implemented?