use correct stat type and fix some redundancy

Author: RalfJung

src/shims/unix/freebsd/foreign_items.rs

@@ -148,7 +148,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let result = this.macos_fbsd_solarish_lstat(path, buf)?;
                 this.write_scalar(result, dest)?;
             }
-            "fstat" | "fstat@FBSD_1.0" => {
+            "fstat@FBSD_1.0" => {
                 let [fd, buf] = this.check_shim_sig_lenient(abi, CanonAbi::C, link_name, args)?;
                 let result = this.fstat(fd, buf)?;
                 this.write_scalar(result, dest)?;

src/shims/unix/fs.rs

@@ -130,7 +130,11 @@ trait EvalContextExtPrivate<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let (modified_sec, modified_nsec) = metadata.modified.unwrap_or((0, 0));
         let mode = metadata.mode.to_uint(this.libc_ty_layout("mode_t").size)?;
 
-        let buf = this.deref_pointer_as(buf_op, this.libc_ty_layout("stat"))?;
+        // We do *not* use `deref_pointer_as` here since determining the right pointee type
+        // is highly non-trivial: it depends on which exact alias of the function was invoked
+        // (e.g. `fstat` vs `fstat64`), and then on FreeBSD it also depends on the ABI level
+        // which can be different between the libc used by std and the libc used by everyone else.
+        let buf = this.deref_pointer(buf_op)?;
         this.write_int_fields_named(
             &[
                 ("st_dev", metadata.dev.into()),
@@ -156,9 +160,6 @@ trait EvalContextExtPrivate<'tcx>: crate::MiriInterpCxExt<'tcx> {
         if matches!(&this.tcx.sess.target.os, Os::MacOs | Os::FreeBsd) {
             this.write_int_fields_named(
                 &[
-                    ("st_atime_nsec", access_nsec.into()),
-                    ("st_mtime_nsec", modified_nsec.into()),
-                    ("st_ctime_nsec", 0),
                     ("st_birthtime", created_sec.into()),
                     ("st_birthtime_nsec", created_nsec.into()),
                     ("st_flags", 0),

src/shims/unix/solarish/foreign_items.rs

@@ -100,11 +100,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let result = this.macos_fbsd_solarish_lstat(path, buf)?;
                 this.write_scalar(result, dest)?;
             }
-            "fstat" | "fstat64" => {
-                let [fd, buf] = this.check_shim_sig_lenient(abi, CanonAbi::C, link_name, args)?;
-                let result = this.fstat(fd, buf)?;
-                this.write_scalar(result, dest)?;
-            }
             "readdir" => {
                 let [dirp] = this.check_shim_sig_lenient(abi, CanonAbi::C, link_name, args)?;
                 let result = this.readdir64("dirent", dirp)?;

tests/pass-dep/libc/libc-fs.rs

@@ -461,13 +461,15 @@ fn test_fstat() {
     let file = File::open(&path).unwrap();
     let fd = file.as_raw_fd();
 
-    let mut stat: libc::stat = unsafe { MaybeUninit::zeroed().assume_init() };
-    let res = unsafe { libc::fstat(fd, &mut stat) };
+    let mut stat = MaybeUninit::<libc::stat>::uninit();
+    let res = unsafe { libc::fstat(fd, stat.as_mut_ptr()) };
     assert_eq!(res, 0);
+    let stat = unsafe { stat.assume_init_ref() };
 
     assert_eq!(stat.st_size, 5);
     assert_eq!(stat.st_mode & libc::S_IFMT, libc::S_IFREG);
 
+    // Check that all fields are initialized.
     let _st_nlink = stat.st_nlink;
     let _st_blksize = stat.st_blksize;
     let _st_blocks = stat.st_blocks;