From 4754b66f72a8fbfd48e30ae0bd12a44d13a4ce10 Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Sun, 1 May 2022 17:50:00 +0200
Subject: 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.
---
 src/lib.rs | 105 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 src/lib.rs

(limited to 'src/lib.rs')

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),
+            );
+        }
+    }
+}
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