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.

1 files changed, 61 insertions, 0 deletions

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();
+}