Improve prctl, add a test.

Author: Vytautas Astrauskas

src/shims/thread.rs

@@ -102,12 +102,17 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
 
         let option = this.read_scalar(option)?.not_undef()?.to_i32()?;
-        if option != this.eval_libc_i32("PR_SET_NAME")? {
-            throw_unsup_format!("Miri supports only PR_SET_NAME");
+        if option == this.eval_libc_i32("PR_SET_NAME")? {
+            let address = this.read_scalar(arg2)?.not_undef()?;
+            let name = this.memory.read_c_str(address)?.to_owned();
+            this.set_active_thread_name(name)?;
+        } else if option == this.eval_libc_i32("PR_GET_NAME")? {
+            let address = this.read_scalar(arg2)?.not_undef()?;
+            let name = this.get_active_thread_name()?;
+            this.memory.write_bytes(address, name)?;
+        } else {
+            throw_unsup_format!("Unsupported prctl option.");
         }
-        let address = this.read_scalar(arg2)?.not_undef()?;
-        let name = this.memory.read_c_str(address)?.to_owned();
-        this.set_active_thread_name(name)?;
 
         Ok(0)
     }

tests/run-pass/concurrency/libc_prctl_thread_name.rs

@@ -0,0 +1,17 @@
+// ignore-windows: No libc on Windows
+
+#![feature(rustc_private)]
+
+extern crate libc;
+
+use std::ffi::CString;
+
+fn main() {
+    unsafe {
+        let thread_name = CString::new("hello").expect("CString::new failed");
+        assert_eq!(libc::prctl(libc::PR_SET_NAME, thread_name.as_ptr() as u64, 0, 0, 0), 0);
+        let mut buf = [0; 6];
+        assert_eq!(libc::prctl(libc::PR_GET_NAME, buf.as_mut_ptr() as u64, 0, 0, 0), 0);
+        assert_eq!(thread_name.as_bytes_with_nul(), buf);
+    }
+}