Auto merge of rust-lang#2465 - RalfJung:strerror_r, r=RalfJung

avoid strerror_r failure on unknown errnum

This is an informative function anyway, so as fallback just return a string with the raw errnum. Avoids panics / interpreter aborts in std on unknown errnum in from_raw_os_error.

Author: bors

src/helpers.rs

@@ -609,20 +609,23 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     }
 
     /// The inverse of `io_error_to_errnum`.
-    fn errnum_to_io_error(
+    #[allow(clippy::needless_return)]
+    fn try_errnum_to_io_error(
         &self,
         errnum: Scalar<Provenance>,
-    ) -> InterpResult<'tcx, std::io::ErrorKind> {
+    ) -> InterpResult<'tcx, Option<std::io::ErrorKind>> {
         let this = self.eval_context_ref();
         let target = &this.tcx.sess.target;
         if target.families.iter().any(|f| f == "unix") {
             let errnum = errnum.to_i32()?;
             for &(name, kind) in UNIX_IO_ERROR_TABLE {
                 if errnum == this.eval_libc_i32(name)? {
-                    return Ok(kind);
+                    return Ok(Some(kind));
                 }
             }
-            throw_unsup_format!("raw errnum {:?} cannot be translated into io::Error", errnum)
+            // Our table is as complete as the mapping in std, so we are okay with saying "that's a
+            // strange one" here.
+            return Ok(None);
         } else {
             throw_unsup_format!(
                 "converting errnum into io::Error is unsupported for OS {}",

src/shims/unix/foreign_items.rs

@@ -465,8 +465,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let buf = this.read_pointer(buf)?;
                 let buflen = this.read_scalar(buflen)?.to_machine_usize(this)?;
 
-                let error = this.errnum_to_io_error(errnum)?;
-                let formatted = error.to_string();
+                let error = this.try_errnum_to_io_error(errnum)?;
+                let formatted = match error {
+                    Some(err) => format!("{err}"),
+                    None => format!("<unknown errnum in strerror_r: {errnum}>"),
+                };
                 let (complete, _) = this.write_os_str_to_c_str(OsStr::new(&formatted), buf, buflen)?;
                 let ret = if complete { 0 } else { this.eval_libc_i32("ERANGE")? };
                 this.write_int(ret, dest)?;

tests/pass/fs.rs

@@ -3,6 +3,7 @@
 
 #![feature(rustc_private)]
 #![feature(io_error_more)]
+#![feature(io_error_uncategorized)]
 
 use std::ffi::CString;
 use std::fs::{
@@ -26,6 +27,7 @@ fn main() {
     test_directory();
     test_canonicalize();
     test_dup_stdout_stderr();
+    test_from_raw_os_error();
 
     // These all require unix, if the test is changed to no longer `ignore-windows`, move these to a unix test
     test_file_open_unix_allow_two_args();
@@ -434,3 +436,11 @@ fn test_dup_stdout_stderr() {
         libc::write(new_stderr, bytes.as_ptr() as *const libc::c_void, bytes.len());
     }
 }
+
+fn test_from_raw_os_error() {
+    let code = 6; // not a code that std or Miri know
+    let error = Error::from_raw_os_error(code);
+    assert!(matches!(error.kind(), ErrorKind::Uncategorized));
+    // Make sure we can also format this.
+    format!("{error:?}");
+}