Implemented truncation for prctl

Author: YohDeadfall

src/shims/unix/android/thread.rs

@@ -20,26 +20,31 @@ pub fn prctl<'tcx>(
     // https://github.com/rust-lang/libc/pull/3941 lands.
     const PR_SET_NAME: i32 = 15;
     const PR_GET_NAME: i32 = 16;
+    const TASK_COMM_LEN: usize = 16;
 
     let [op] = check_min_arg_count("prctl", args)?;
     let res = match this.read_scalar(op)?.to_i32()? {
         PR_SET_NAME => {
             let [_, name] = check_min_arg_count("prctl(PR_SET_NAME, ...)", args)?;
 
-            let tid = this.pthread_self()?;
-            let name = this.read_scalar(name)?;
-            let name_len = 16;
+            let name = this.read_scalar(name)?.to_pointer(this)?;
+            let name =
+                this.read_c_str(name)?.iter().take(TASK_COMM_LEN - 1).copied().collect::<Vec<_>>();
+
+            let thread = this.pthread_self()?.to_int(this.libc_ty_layout("pthread_t").size)?;
+            let thread = ThreadId::try_from(thread).unwrap();
 
-            this.pthread_setname_np(tid, name, name_len)?
+            this.set_thread_name(thread, name);
+            Scalar::from_u32(0)
         }
         PR_GET_NAME => {
             let [_, name] = check_min_arg_count("prctl(PR_GET_NAME, ...)", args)?;
 
-            let tid = this.pthread_self()?;
+            let thread = this.pthread_self()?;
             let name = this.read_scalar(name)?;
-            let name_len = Scalar::from_target_usize(16, this);
+            let name_len = Scalar::from_target_usize(TASK_COMM_LEN as u64, this);
 
-            this.pthread_getname_np(tid, name, name_len)?
+            this.pthread_getname_np(thread, name, name_len)?
         }
         op => {
             this.handle_unsupported_foreign_item(format!("can't execute prctl with OP {op}"))?;

tests/pass-dep/libc/threadname.rs

@@ -1,7 +1,5 @@
 //@ignore-target: windows # No pthreads and prctl on Windows
 use std::ffi::CStr;
-#[cfg(not(target_os = "freebsd"))]
-use std::ffi::CString;
 use std::thread;
 
 fn main() {
@@ -69,10 +67,11 @@ fn main() {
 
         // Also test directly calling pthread_setname to check its return value.
         assert_eq!(set_thread_name(&cstr), 0);
-        // But with a too long name it should fail (except on FreeBSD where the
-        // function has no return, hence cannot indicate failure).
-        #[cfg(not(target_os = "freebsd"))]
-        assert_ne!(set_thread_name(&CString::new(long_name).unwrap()), 0);
+        // But with a too long name it should fail except:
+        // * on FreeBSD where the function has no return, hence cannot indicate failure,
+        // * on Android where prctl silently truncates the string.
+        #[cfg(not(any(target_os = "freebsd", target_os = "android")))]
+        assert_ne!(set_thread_name(&std::ffi::CString::new(long_name).unwrap()), 0);
     });
     result.unwrap().join().unwrap();
 }