https://github.com/johannst/rv64i-linux-user-no-std

rv64i linux userspace no_std
https://github.com/johannst/rv64i-linux-user-no-std

nostd nostdlib qemu risc-v riscv rust syscall

Last synced: about 1 year ago
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rv64i linux userspace no_std

• Host: GitHub
• URL: https://github.com/johannst/rv64i-linux-user-no-std
• Owner: johannst
• License: mit
• Created: 2022-11-10T21:04:21.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2022-11-13T14:13:40.000Z (over 3 years ago)
• Last Synced: 2025-01-22T01:36:32.611Z (over 1 year ago)
• Topics: nostd, nostdlib, qemu, risc-v, riscv, rust, syscall
• Language: Rust
• Homepage:
• Size: 6.84 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# riscv64i `#[no_std]` Linux user space example

This repository serves to my later self as reference to document some

`#[no_std]` and inline assembly features as well as cargo configurations.

It builds a `riscv64i` Linux user space binary which invokes some syscalls

according to the Linux [syscall(2)

ABI](https://man7.org/linux/man-pages/man2/syscall.2.html) for riscv.

```txt

Arch/ABI    Instruction           System  Ret  Ret  Error    Notes

                                  call #  val  val2

───────────────────────────────────────────────────────────────────

riscv       ecall                 a7      a0   a1   -

Arch/ABI      arg1  arg2  arg3  arg4  arg5  arg6  arg7  Notes

──────────────────────────────────────────────────────────────

riscv         a0    a1    a2    a3    a4    a5    -

```

The syscalls are implemented in [lib.rs](src/lib.rs).

When building, cargo runs the [build.rs](build.rs) script before building the

crate itself, which in this case generates some rust code for the syscall

numbers from the riscv C headers.

Looking into [.cargo/config](.cargo/config) we actually build for the

`riscv64imac-unknown-none-elf` rather than the `riscv64gc-unknown-linux-gnu`

target, as our goal is to build a `risv64*i*` binary and that way we just have

to disable a few more extensions :^).

The binary can be automatically run in the QEMU user space emulator with `cargo

run`, this is because the `runner` is specified in

[.cargo/config](.cargo/config).

## Requirements

- `riscv64-linux-gnu-gcc` toolchain for parsing syscall numbers in

  [build.rs](build.rs)

- `riscv64imac-unknown-none-elf` rustc target to generate riscv target code

  (`rustup target add riscv64imac-unknown-none-elf`)

- `qemu-riscv64` QEMU userspace emulator