initial commit

Build small no_std example for rv64i target.

This code executes some linux syscalls as demo and therefore expects to
be executed in rv64 linux.

7 files changed, 211 insertions, 0 deletions

diff --git a/.cargo/config b/.cargo/config
new file mode 100644
index 0000000..6588394
--- /dev/null
+++ b/.cargo/config
@@ -0,0 +1,9 @@
+[build]
+target = "riscv64imac-unknown-none-elf"
+
+[target.riscv64imac-unknown-none-elf]
+# Effectively build for rv64i.
+rustflags = ["-C", "target-feature=-m,-a,-c"]
+runner    = "qemu-riscv64"
+#runner    = "qemu-riscv64 -d in_asm"
+#runner    = "qemu-riscv64 -strace"
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..51c8e32
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "user-sw"
+version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..f7e203e
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name    = "user-sw"
+version = "0.1.0"
+authors = ["Johannes Stoelp"]
+edition = "2021"
+license = "<TODO>"
+
+[dependencies]
diff --git a/build.rs b/build.rs
new file mode 100644
index 0000000..827c302
--- /dev/null
+++ b/build.rs
@@ -0,0 +1,61 @@
+/// Generate rust constants for linux riscv syscall numbers.
+///
+/// Syscall numbers are parsed from the `linux/unistd.h` header.
+/// This script uses the `riscv64-linux-gnu-*` tools to find to header, make sure those tools are
+/// in the PATH.
+///
+/// For simplicity, this script unwraps any Option/Result because we want to fail in case of any
+/// error.
+
+fn main() {
+    // Get sysroot to find header location.
+    let out = std::process::Command::new("riscv64-linux-gnu-gcc")
+        .arg("-print-sysroot")
+        .output()
+        .unwrap();
+    let sysroot = std::str::from_utf8(&out.stdout).unwrap();
+    let header = format!("{}/include/linux/unistd.h", sysroot.trim_end());
+
+    // The header should "basically" never change.
+    println!("cargo:rerun-if-changed={}", header);
+
+    // Run header through preprocessor and dump macro definitions.
+    let out = std::process::Command::new("riscv64-linux-gnu-cpp")
+        .arg("-dM")
+        .arg(header)
+        .output()
+        .unwrap();
+    let defines = std::str::from_utf8(&out.stdout).unwrap();
+
+    let mut output = String::with_capacity(256);
+
+    // Parse out lines of the format
+    //   #define __NR_<syscall> <nr>
+    // and generate output strings.
+    for line in defines.lines() {
+        let line = match line.strip_prefix("#define __NR_") {
+            Some(line) => line,
+            None => continue,
+        };
+
+        let (sys, nr) = match line.split_once(' ') {
+            Some(split) => split,
+            None => continue,
+        };
+
+        let nr = match nr.parse::<usize>() {
+            Ok(nr) => nr,
+            Err(_) => continue,
+        };
+
+        output.push_str(&format!(
+            "#[allow(unused)] const SYS_{}: usize = {};\n",
+            sys.to_uppercase(),
+            nr
+        ));
+    }
+
+    // Write out rust file with syscall numbers.
+    let outfile = format!("{}/syscalls.rs", std::env::var("OUT_DIR").unwrap());
+    std::fs::write(&outfile, output).unwrap();
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..3191f8d
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,105 @@
+#![no_std]
+
+/// Raw file descriptor.
+///
+/// Instances of `Fd` can be constructed with [`stdout()`] and [`stderr()`].
+pub struct Fd(i32);
+
+impl core::fmt::Write for Fd {
+    fn write_str(&mut self, s: &str) -> Result<(), core::fmt::Error> {
+        if sys::write(self.0, s.as_bytes()) != -1 {
+            Ok(())
+        } else {
+            Err(core::fmt::Error)
+        }
+    }
+}
+
+/// Construct raw file descriptor for `stdout`.
+pub fn stdout() -> Fd {
+    Fd(1)
+}
+
+/// Construct raw file descriptor for `stderr`.
+pub fn stderr() -> Fd {
+    Fd(2)
+}
+
+/// Write format string to `stdout`, swallowing any errors.
+#[macro_export]
+macro_rules! println {
+    () => ({
+        $crate::println!("")
+    });
+    ($($arg:tt)*) => ({
+        use core::fmt::Write;
+        let _ = writeln!(&mut $crate::stdout(), $($arg)*);
+    });
+}
+
+/// Write format string to `stderr`, swallowing any errors.
+#[macro_export]
+macro_rules! eprintln {
+    () => ({
+        $crate::eprintln!("")
+    });
+    ($($arg:tt)*) => ({
+        use core::fmt::Write;
+        let _ = writeln!(&mut $crate::stderr(), $($arg)*);
+    });
+}
+
+/// Wrapper to invoke `riscv` linux syscalls.
+///
+/// Syscalls are generated according to the linux [syscall(2)][man-syscall] abi.
+///
+/// # Invocation
+/// ```
+/// Arch/ABI  Instruction  System  Ret  Ret
+///                        call #  val  val2
+/// ----------------------------------------
+/// riscv     ecall        a7      a0   a1
+/// ```
+///
+/// # Arguments
+/// ```
+/// Arch/ABI  arg1  arg2  arg3  arg4  arg5  arg6
+/// --------------------------------------------
+/// riscv     a0    a1    a2    a3    a4    a5
+/// ```
+///
+/// [man-syscall]: https://man7.org/linux/man-pages/man2/syscall.2.html
+#[cfg(target_arch = "riscv64")]
+pub mod sys {
+    use core::arch::asm;
+
+    // Include generated syscall numbers (build.rs).
+    include!(concat!(env!("OUT_DIR"), "/syscalls.rs"));
+
+    #[inline]
+    pub fn write(fd: i32, buf: &[u8]) -> i32 {
+        let mut ret;
+        unsafe {
+            asm!(
+                "ecall",
+                in("a7") SYS_WRITE,
+                inlateout("a0") fd => ret,
+                in("a1") buf.as_ptr(),
+                in("a2") buf.len(),
+            );
+        }
+        ret
+    }
+
+    #[inline]
+    pub fn exit(status: i32) -> ! {
+        unsafe {
+            asm!(
+                "ecall",
+                in("a7") SYS_EXIT,
+                in("a0") status,
+                options(noreturn),
+            );
+        }
+    }
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..f1ea8b0
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,20 @@
+#![no_std]
+#![no_main]
+
+use user_sw::{eprintln, println, sys};
+
+fn main() {
+    println!("Hello {} from rust main().", 1337);
+}
+
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    main();
+    sys::exit(0);
+}
+
+#[panic_handler]
+fn panic_handler(info: &core::panic::PanicInfo) -> ! {
+    eprintln!("{}", info);
+    sys::exit(42);
+}