Linux Proxy Kernel

[David Castells Rufas]

Hi,

Spike implements a proxy kernel to provide a minimal set of syscalls.

(to run applications compiled with riscv64-unknown-elf-gcc)

Then, it provides a bootloader to be able to boot Linux
(and be able to run applications compiled with riscv64-unkown-linux-gnu-gcc).

Does anyone know why they didn't provide a proxy kernel for the Linux syscalls instead ?

Do you know it anyone tried to do this (before myself) ?

BR

[Tommy Murphy]

Doesn't this explain it?

https://github.com/riscv-software-src/riscv-pk

"The RISC-V Proxy Kernel, pk, is a lightweight application execution environment that can host statically-linked RISC-V ELF binaries. It is designed to support tethered RISC-V implementations with limited I/O capability and thus handles I/O-related system calls by proxying them to a host computer."

[Tommy Murphy]

Also - as far as I recall the BBL is effectively deprecated in favour of something like OpenSBI?

[David Castells Rufas]

No, this explains what pk does, i.e. intercepting the syscalls (when executing ECALL instructions) generated by bare-metal applications (compiled with riscv64-unknown-elf-gcc).
The proposed method to simulate Linux applications is to execute the full Linux Kernel on spike, which is a considerable larger piece of code (and time). Moreover, by executing full Linux you cannot access host resources (like files) when running the target (RISC-V) system. 

I am asking because I am implementing a Linux proxy-kernel for the punxa RISC-V python-based simulator (https://github.com/davidcastells/punxa/tree/main/test/proxykernel_linux/hello) and I would like to know...

1) Why Spike didn't go this way ? Is there a problem I missed that will  seriously limit its usefulness. I already succesfully tested a "hello world" application and I find it quite interesting for teaching purposes.  
2) Did anybody make the same/similar experiment before ? 

[Christoph Müllner]

QEMU provides user space emulation
(https://qemu-project.gitlab.io/qemu/user/index.html).

>
> BR
>
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[David Castells Rufas]

You are right. Thanks