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A comment on Valve is testing ARM64 support for popular games. Parent comment

Re:Valve is testing ARM64 support for popular games by agosz on Monday September 23, 2024 @06:39PM (#41631343)
ARM64EC doesn't really make your code JITable. It is ARM64 code with thunks to enable transitions to x64 code. That's why it runs at near native speeds; not because of the JIT. The x64 portions of the binary do get JITed though, but the ARM64EC portions are usually much faster.

All x64 code gets JITed but that's regardless of whether ARM64EC is used or not; ARM64EC allows ARM64 applications to interface with x64 binaries.

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Re:Valve is testing ARM64 support for popular games by sedatk on Monday September 23, 2024 @09:34PM (#41632320)
Okay, I had assumed JIT for x64 wasn't possible (yet) and ARM64EC enabled that partially. So, ARM64EC images are actually native ARM code that can interact with emulated (+JITted) components. For some reason, I thought native ARM64 binaries already had this capability, but they don't. Thanks, that's actually a better state of affairs in Windows on ARM land.
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Re:Valve is testing ARM64 support for popular games by agosz on Tuesday September 24, 2024 @12:26AM (#41633103)
Yes, that's correct! Unfortunately ARM64 can't fully interface with x64 code (e.g. you can't translate an ARM64 CONTEXT to an x64 one directly due to differing numbers of registers), so the backwards compatibility is restricted to ARM64EC only.
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