Building a 64-bit aarch64 kernel and userspace for the Raspberry Pi 4

Re:Building a 64-bit aarch64 kernel and userspace for the Ra... by lokedhs on Saturday November 16, 2019 @10:14AM (#21553002)

Does it? What does the 64-bit mode provide that the 32-bit one doesn't? On x86 things were different because the 64-bit ABI also provided access to more registers and other benefits, but as far as I know, the 32-bit mode has the same features as 64-bit on ARM.

This reminds me of when the UltraSPARC CPU's came out. I was working at Sun at the time, and I remember asking why Solaris 2.6 was released without 64-bit support. The reason was the same, there was really no benefit to it (except for support for more than 4 GB of RAM in a single process, which wasn't really needed back then).

Even as later versions of Solaris came out with native 64-bit support, the entire userspace was still 32-bit because it worked on both architectures, and the binaries were both smaller and also faster.

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Re:Building a 64-bit aarch64 kernel and userspace for the Ra... by Tuna-Fish on Saturday November 16, 2019 @10:26AM (#21553078)

> On x86 things were different because the 64-bit ABI also provided access to more registers and other benefits, but as far as I know, the 32-bit mode has the same features as 64-bit on ARM.

It doesn't. 64-bit arm has 31 GPRs. It also has much cleaner decode and some low-end cpus that can do it and 32-bit execute it faster than they do 32-bit code.

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Re:Building a 64-bit aarch64 kernel and userspace for the Ra... by lokedhs on Saturday November 16, 2019 @10:40AM (#21553155)

Thank you for the clarification. I didn't know that.

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Re:Building a 64-bit aarch64 kernel and userspace for the Ra... by gonzo on Sunday November 17, 2019 @01:09AM (#21556767)

But you worked at Sun?

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Re:Building a 64-bit aarch64 kernel and userspace for the Ra... by lokedhs on Monday November 18, 2019 @04:15AM (#21562910)

I did. But Sun never used ARM. They used SPARC, and later x86.

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