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A comment on Writing ARM64 Code for Apple Platforms. Parent comment

Re:Writing ARM64 Code for Apple Platforms by NobodyNada on Thursday June 24, 2021 @12:52PM (#27620320)
> On Darwin, x18 is used [...] on hardware where Meltdown mitigations are needed. [...] On M1, it's currently usable by applications

I’m confused. x18 is an ARM register, but I thought Meltdown only affected x86 chips. Were iOS devices vulnerable to Meltdown too? Or did you mean not x18 specifically but some equivalent OS-reserved x86 register?

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Re:Writing ARM64 Code for Apple Platforms by somebody_amzn on Thursday June 24, 2021 @12:55PM (#27620388)
Yeah, Meltdown did affect quite some Arm CPUs, including the Cortex-A75 too.

However, due to specific features of the Arm architecture, it was patchable without a significant performance hit.

(see this section: https://siguza.github.io/KTRR/#meltdownspectre-mitigations-1..., which made the need for actually doing a page table switch avoidable)

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Re:Writing ARM64 Code for Apple Platforms by NobodyNada on Thursday June 24, 2021 @01:05PM (#27620574)
Interesting, thanks for the link!
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