# Getting Ready for APX extensions to x64

**URL:** https://racket.discourse.group/t/getting-ready-for-apx-extensions-to-x64/4342
**Category:** Internals
**Created:** [August 5, 2026, 1:56am UTC](https://racket.discourse.group/t/getting-ready-for-apx-extensions-to-x64/4342 "2026-08-05T01:56:30Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![ndykman](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/ndykman/32/2140_2.png) [@ndykman](https://racket.discourse.group/u/ndykman)
#### Post date: [August 5, 2026, 1:56am UTC](https://racket.discourse.group/t/getting-ready-for-apx-extensions-to-x64/4342/1 "2026-08-05T01:56:30Z")

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Nothing pressing since the hardware isn't out yet, but there is a lot of stuff there that may impact things. One is an addition to the Win64 calling convention in that registers `R30` and `R31` (if available) are non-volatile. I don't know if ChezScheme still uses a custom `setjmp` and `longjmp`, but if so, that might need to change to account for that.

The other big thing is three argument instructions and potential optimizations around that.