Auto merge of rust-lang#3953 - YohDeadfall:glibc-thread-name, r=RalfJung

Fixed pthread_getname_np impl for glibc

The behavior of `glibc` differs a bit different for `pthread_getname_np` from other implementations. It requires the buffer to be at least 16 bytes wide without exception.

[Docs](https://www.man7.org/linux/man-pages/man3/pthread_setname_np.3.html):

```
The pthread_getname_np() function can be used to retrieve the
name of the thread.  The thread argument specifies the thread
whose name is to be retrieved.  The buffer name is used to return
the thread name; size specifies the number of bytes available in
name.  The buffer specified by name should be at least 16
characters in length.  The returned thread name in the output
buffer will be null terminated.
```

[Source](https://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/pthread_getname.c;hb=dff8da6b3e89b986bb7f6b1ec18cf65d5972e307#l37):

```c
int
__pthread_getname_np (pthread_t th, char *buf, size_t len)
{
  const struct pthread *pd = (const struct pthread *) th;

  /* Unfortunately the kernel headers do not export the TASK_COMM_LEN
     macro.  So we have to define it here.  */
#define TASK_COMM_LEN 16
  if (len < TASK_COMM_LEN)
    return ERANGE;
```

Author: bors

src/tools/miri/src/shims/unix/linux/foreign_items.rs

@@ -9,6 +9,11 @@ use crate::machine::{SIGRTMAX, SIGRTMIN};
 use crate::shims::unix::*;
 use crate::*;
 
+// The documentation of glibc complains that the kernel never exposes
+// TASK_COMM_LEN through the headers, so it's assumed to always be 16 bytes
+// long including a null terminator.
+const TASK_COMM_LEN: usize = 16;
+
 pub fn is_dyn_sym(name: &str) -> bool {
     matches!(name, "statx")
 }
@@ -74,22 +79,29 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             "pthread_setname_np" => {
                 let [thread, name] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let max_len = 16;
                 let res = this.pthread_setname_np(
                     this.read_scalar(thread)?,
                     this.read_scalar(name)?,
-                    max_len,
+                    TASK_COMM_LEN,
                 )?;
                 this.write_scalar(res, dest)?;
             }
             "pthread_getname_np" => {
                 let [thread, name, len] =
                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
-                let res = this.pthread_getname_np(
-                    this.read_scalar(thread)?,
-                    this.read_scalar(name)?,
-                    this.read_scalar(len)?,
-                )?;
+                // The function's behavior isn't portable between platforms.
+                // In case of glibc, the length of the output buffer must
+                // be not shorter than TASK_COMM_LEN.
+                let len = this.read_scalar(len)?;
+                let res = if len.to_target_usize(this)? < TASK_COMM_LEN as u64 {
+                    this.eval_libc("ERANGE")
+                } else {
+                    this.pthread_getname_np(
+                        this.read_scalar(thread)?,
+                        this.read_scalar(name)?,
+                        len,
+                    )?
+                };
                 this.write_scalar(res, dest)?;
             }
             "gettid" => {

src/tools/miri/tests/pass-dep/libc/pthread-threadname.rs

@@ -5,6 +5,9 @@ use std::ffi::CString;
 use std::thread;
 
 fn main() {
+    // The short name should be shorter than 16 bytes which POSIX promises
+    // for thread names. The length includes a null terminator.
+    let short_name = "test_named".to_owned();
     let long_name = std::iter::once("test_named_thread_truncation")
         .chain(std::iter::repeat(" yada").take(100))
         .collect::<String>();
@@ -48,23 +51,64 @@ fn main() {
         }
     }
 
-    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()));
+    thread::Builder::new()
+        .name(short_name.clone())
+        .spawn(move || {
+            // Rust remembers the full thread name itself.
+            assert_eq!(thread::current().name(), Some(short_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()));
+            // Note that glibc requires 15 bytes long buffer exculding a null terminator.
+            // Otherwise, `pthread_getname_np` returns an error.
+            let mut buf = vec![0u8; short_name.len().max(15) + 1];
+            assert_eq!(get_thread_name(&mut buf), 0);
 
-        // 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);
-    });
-    result.unwrap().join().unwrap();
+            let cstr = CStr::from_bytes_until_nul(&buf).unwrap();
+            // POSIX seems to promise at least 15 chars excluding a null terminator.
+            assert_eq!(short_name.as_bytes(), cstr.to_bytes());
+
+            // Also test directly calling pthread_setname to check its return value.
+            assert_eq!(set_thread_name(&cstr), 0);
+
+            // For glibc used by linux-gnu there should be a failue,
+            // if a shorter than 16 bytes buffer is provided, even if that would be
+            // large enough for the thread name.
+            #[cfg(target_os = "linux")]
+            assert_eq!(get_thread_name(&mut buf[..15]), libc::ERANGE);
+        })
+        .unwrap()
+        .join()
+        .unwrap();
+
+    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.
+            // Note that there's no specific to glibc buffer requirement, since the value
+            // `long_name` is longer than 16 bytes including a null terminator.
+            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();
+            // POSIX seems to promise at least 15 chars excluding a null terminator.
+            assert!(
+                cstr.to_bytes().len() >= 15,
+                "name is too short: len={}",
+                cstr.to_bytes().len()
+            );
+            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 (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);
+        })
+        .unwrap()
+        .join()
+        .unwrap();
 }