---
tags: Computer Architecture
---
# RVVM
contributed by <`huang-me`>, <`OliveLake`>
:::info
Expectation
- [x] RVVM ( https://github.com/LekKit/RVVM ) 同時支援 RV64 和 RV32，本課程著重於
RV32，請針對 RV32 準備相關的開發工具 (可重用 GNU Toolchain)
- [x] 留意 Linux 啟動流程: OpenSBI -> U-Boot -> Linux kernel ->
userspace，請學習相關的背景知識，說明個別元件的作用，特別是 OpenSBI
- [ ] 準備 RV32 的 Linux 核心，你們可能會遭遇技術困難，記錄下來並嘗試排除
- [ ] 說明 Linux 核心在 RV32/RVVM 啟動過程中，除了 CPU，還有哪些週邊的互動 (如中斷控制器和 timer)
- [ ] RVVM 可通過 RISC-V compliance tests，請以最新的程式碼搭配新的測試，確認在 RV32 (及相關
extension) 得以通過，並記錄過程，若發現問題就回報給 RVVM 開發團隊.
:::
## Introduction
As shown in figure below
RVVM replace QEMU, and we need to prepare `OS kernel` & `cross compiler tools` & ==Distributions== for it.
## Prerequisites to build RVVM
### Build riscv32 linux toolchain
There are two types riscv-gnu-toolchain,
1. `riscv32-unknown-elf-gcc`, cross compiler using newlib for 32bit
RISC-V bare-metal.
2. `riscv32-unknown-linux-gnu-gcc`, corss compiler using glibc which provides the core libraries for GNU/Linux systems.
:::spoiler stupid try
## Why wrong
**Toolchain leading with `riscv-none-embed-` is toolchain for ==embedded system==.
We're going to build risc-v linux, so we need toolchain leading with `riscv64-unknown-linux-gnu-`.**
### Build OpenSBI
```shell=
export CROSS_COMPILE=riscv-none-embed-
git clone https://github.com/starfive-tech/opensbi.git
cd opensbi
make PLATFORM="generic"
```
- `fw_jump.bin` will be generated in
`opensbi/build/platform/generic/firmware`
### Build linux kernel
```shell=
// generate config
make ARCH=riscv CROSS_COMPILE=riscv-none-embed- defconfig
// compile
make ARCH=riscv CROSS_COMPILE=riscv-none-embed- -j 4
```
- `Image` will be generated in
`linux/arch/riscv/boot`
### Build busy box
```shell=
git clone https://git.busybox.net/busybox
cd busybox
CROSS_COMPILE=riscv-none-embed- make menuconfig
CROSS_COMPILE=riscv-none-embed- make // error
```
:::danger
```
include/platform.h:168:11: fatal error: byteswap.h: No such file or directory
168 | # include <byteswap.h>
| ^~~~~~~~~~~~
```
riscv-none-embed- has no `byteswap.h`
:::
#### Prerequisite
For ubuntu, there are some needed packages to build toolchain.
```
$ sudo apt-get install autoconf automake autotools-dev curl python3 libmpc-dev libmpfr-dev libgmp-dev gawk build-essential bison flex texinfo gperf libtool patchutils bc zlib1g-dev libexpat-dev
```
#### Installation
```shell
git clone https://github.com/riscv-collab/riscv-gnu-toolchain.git --recursive
cd riscv-gnu-toolchain
./configure --prefix=/opt/riscv32-linux --with-arch=rv32imc --enable-linux
sudo make linux
```
#### Errors in building riscv linux toolchain
After `sudo make linux`
```
error : mips nios2 powerpc riscv glibc requires the A extension
```
Because RISC-V Linux require `A-extension` as minimal requirement, so at least we should use `--wtih-arch=rv32ia` or `--with-arch=rv64ia` for building linux toolchain. We sholud use
```
make clean
./configure --prefix=opt/riscv32-linux --with-arch=rv32imac --enable-linux
make linux
```
==PICTURE==
### Setup toolchain & environment variable
```shell
export PATH=$PATH:/opt/riscv32-linux/bin
export CROSS_COMPILE=riscv32-unknown-linux-gnu-
export ARCH=riscv
```
## Introduction for Boot flow
### RISC-V Upstream Boot Flow
* ZSBL(Zeroth Stage Boot Loader): Initial platform-specific bootloader,the first program being run after power-on. Core starts fetching from ROM of SoC, copying FSBL image from SD into memory.
* FSBL(first Stage Boot Loader): Initial platform-specific bootloader. FSBL is SiFive specific and will be replaced by Coreboot/U-Boot SPL.
:::spoiler What is U-Boot SPL
Usually regular bootloader (e.g. U-Boot) binary is bigger than SRAM, So we need to create some additional bootloader, referred as first-stage bootloader (in two-stage bootloader scenario).
Regularly the first-stage bootloader is U-Boot SPL, and the second-stage bootloader is U-Boot.
:::
<br>
* OpenSBI: The RISC-V Supervisor Binary Interface (SBI) specifications. Aimed at providing RUNTIME services in M-mode, typically used in boot stage following ROM/LOADER.
:::warning
RVVM allows boot the Linux kernel directly after SBI, without U-Boot. Therefore we need to execute `fw_jump.bin` which contain OpenSBI and initial firmware.
:::
* fw_jump: Firmware provides by OpenSBI with `static` jump address to the next booting stage, so previous booting stage (i.e. LOADER) has to load next booting stage (i.e. BOOTLADER) at a fixed location.
### Build linux kernel image
Create simple Hello world of booting Linux on RVVM
```
mkdir riscv32-linux
cd riscv32-linux
git clone https://github.com/torvalds/linux
git checkout v5.4.0
make ARCH=riscv CROSS_COMPILE=riscv32-unknown-linux-gnu- defconfig
```
### Build U-Boot
```shell=
git clone https://github.com/u-boot/u-boot.git
make qemu-riscv32_smode_defconfig
make
```
### Build OpenSBI
```shell
git clone https://github.com/starfive-tech/opensbi.git
cd opensbi
make PLATFORM="generic" FW_PAYLOAD_PATH=../u-boot/u-boot.bin
```
error occurs
```
cc: error: unrecognized argument in option ‘-mabi=lp64’
cc: note: valid arguments to ‘-mabi=’ are: ms sysv
cc: error: unrecognized argument in option ‘-mcmodel=medany’
cc: note: valid arguments to ‘-mcmodel=’ are: 32 kernel large medium small; did you mean ‘medium’?
```
Caused by failing to use RISC-V compiler, reset path:
```
export CROSS_COMPILE=/opt/riscv32-unknown-linux-gnu-
```
`fw_jump.bin` will be generated in `opensbi/build/platform/generic/firmware`
## Build RVVM
Build RVVM using GNU make on linux
```
git clone https://github.com/LekKit/RVVM
cd RVVM
make
```
There is an error about `no such file or directory : X11/keysym.h & X11/extentions/XShm.h`
Solution :
```
sudo apt install libx11-dev
sudo apt install x11proto-xext-dev
```
Then keep building RVVM
```
cd release.linux.riscv
./rvvm_riscv fw_jump.bin -kernel linux_Imag -mem 2G -smp 2 -res 1280x720
```
:::danger
loop forever
:::
After contact with RVVM team, it seems like we are running U-Boot as SBI payload, and U-Boot tries to access MMC flash - RVVM doesn't support flash (yet), so U-Boot keep resets the VM.
One solution is we built U-Boot with IDE (ATA) hard-drives, and another way is we boot the Linux kernel directly after SBI, without U-Boot.
==Rebuild without U-Boot==
```
make PLATFORM="generic"
```
```
cd release.linux.riscv
./rvvm_riscv fw_jump.bin -kernel linux_Imag
```
### Build Distributions
There is not that much pre-built distributions for 32-bit RISC-V, so we use `Buildroot`
```
./rvvm_riscv fw_jump.bin -kernel linux_image -image rootfs.img -mem 1G -res 1280x720
```
### Complience Test
#### What complience test for?
Due to RISC-V is an open ISA, and the freedom of extending the ISA with custom instructions and extensions, the compliance tests are essential to confirm the basic operation is in accordance with the specification
#### Start Test
TODO
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