Added support for prctl handling thread names

Author: YohDeadfall

src/shims/unix/linux/foreign_items.rs

@@ -72,6 +72,60 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             }
 
             // Threading
+            "prctl" => {
+                // We do not use `check_shim` here because `syscall` is variadic. The argument
+                // count is checked bellow.
+                this.check_abi_and_shim_symbol_clash(abi, Abi::C { unwind: false }, link_name)?;
+
+                if args.is_empty() {
+                    throw_ub_format!(
+                        "incorrect number of arguments for prctl: got 0, expected at least 1"
+                    );
+                }
+
+                // Since only two prctl calls are currently handled, and both expext just two arguments,
+                // it makes sense to handle validation here, outside of the match block below.
+                if args.len() < 2 {
+                    throw_ub_format!(
+                        "incorrect number of arguments for `PR_SET_NAME` prctl: got {}, expected at least 2",
+                        args.len()
+                    );
+                }
+
+                for (i, arg) in args.iter().enumerate() {
+                    let val = this.read_scalar(arg)?.to_i32()?;
+                    if val != 0 {
+                        throw_ub_format!(
+                            "incorrect value of {}th argument for 'PR_SET_NAME' prctl: got {}, expected 0L",
+                            i,
+                            val
+                        );
+                    }
+                }
+
+                let op = this.read_scalar(&args[0])?.to_i32()?;
+                let pr_set_name = this.eval_libc_i32("PR_SET_NAME");
+                let pr_get_name = this.eval_libc_i32("PR_GET_NAME");
+
+                let res = match op {
+                    op if op == pr_set_name => {
+                        let tid = this.linux_gettid()?;
+                        let name = this.read_scalar(&args[1])?;
+                        let name_len = 16;
+
+                        this.pthread_setname_np(tid, name, name_len)?
+                    }
+                    op if op == pr_get_name => {
+                        let tid = this.linux_gettid()?;
+                        let name = this.read_scalar(&args[1])?;
+                        let name_len = Scalar::from_target_usize(16, this);
+
+                        this.pthread_getname_np(tid, name, name_len)?
+                    }
+                    _ => return Ok(EmulateItemResult::NotSupported),
+                };
+                this.write_scalar(res, dest)?;
+            }
             "pthread_setname_np" => {
                 let [thread, name] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;

tests/pass-dep/libc/prctl.rs

@@ -0,0 +1,56 @@
+//@ignore-target: windows # No prctl on Windows
+//@ignore-target: apple # No prctl on macOS
+use std::ffi::CStr;
+use std::ffi::CString;
+use std::thread;
+
+fn main() {
+    let long_name = std::iter::once("test_named_thread_truncation")
+        .chain(std::iter::repeat(" yada").take(100))
+        .collect::<String>();
+
+    fn set_thread_name(name: &CStr) -> i32 {
+        cfg_if::cfg_if! {
+            if #[cfg(any(target_os = "linux", target_os = "illumos", target_os = "solaris", target_os = "freebsd"))] {
+                unsafe { libc::pthread_setname_np(libc::pthread_self(), name.as_ptr().cast()) }
+            } else {
+                compile_error!("set_thread_name not supported for this OS")
+            }
+        }
+    }
+
+    fn get_thread_name(name: &mut [u8]) -> i32 {
+        cfg_if::cfg_if! {
+            if #[cfg(any(
+                target_os = "linux",
+                target_os = "illumos",
+                target_os = "solaris",
+                target_os = "freebsd",
+            ))] {
+                unsafe {
+                    libc::pthread_getname_np(libc::pthread_self(), name.as_mut_ptr().cast(), name.len())
+                }
+            } else {
+                compile_error!("get_thread_name not supported for this OS")
+            }
+        }
+    }
+
+    let result = thread::Builder::new().name(long_name.clone()).spawn(move || {
+        // Rust remembers the full thread name itself.
+        assert_eq!(thread::current().name(), Some(long_name.as_str()));
+
+        // But the system is limited -- make sure we successfully set a truncation.
+        let mut buf = vec![0u8; long_name.len() + 1];
+        assert_eq!(get_thread_name(&mut buf), 0);
+        let cstr = CStr::from_bytes_until_nul(&buf).unwrap();
+        assert!(cstr.to_bytes().len() >= 15, "name is too short: len={}", cstr.to_bytes().len()); // POSIX seems to promise at least 15 chars
+        assert!(long_name.as_bytes().starts_with(cstr.to_bytes()));
+
+        // 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.
+        assert_ne!(set_thread_name(&CString::new(long_name).unwrap()), 0);
+    });
+    result.unwrap().join().unwrap();
+}