this post was submitted on 02 Nov 2023
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RISC-V
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RISC-V (pronounced "risk-five") is a license-free, modular, extensible instruction set architecture (ISA).
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Very little information about this. Can't even tell if it is going to be 32-bit or 64-bit.
There have been open source cores for running on FPGAs available for some time. Most work seem to have been for 64-bit, so this seems likely.
A "capability" (in this context) is a pointer with bounds and access rights built in. Memory tagging in hardware makes capabilities unforgeable. Cheri/RISC-V allows for multiple models: Full, hybrid and legacy. In the full model, capabilities and Cheri instructions are used instead of pointers and normal instructions — and buffer overflows are impossible. In hybrid models, capabilities are used to protect certain resources, or used for compartmentalisation within a program (cap inside legacy, or legacy inside cap). The downside is that a stored capability is twice as large as a normal pointer. 128 bits on 64-bit systems and 64 bits on 32-bit systems ... despite bounds being "compressed" using a floating-point like encoding to have larger granularity the larger they are.
Wow. I remember seeing something like this in description of ELBRUS architecture.
Interesting. Thank you.