make unix path handling on Windows hosts preserve absoluteness

README.md

@@ -581,7 +581,7 @@ extern "Rust" {
     /// Performs conversion of path separators as needed.
     ///
     /// Usually Miri performs this kind of conversion automatically. However, manual conversion
-    /// might be necessary when reading an environment variable that was set of the host
+    /// might be necessary when reading an environment variable that was set on the host
     /// (such as TMPDIR) and using it as a target path.
     ///
     /// Only works with isolation disabled.

src/shims/os_str.rs

@@ -174,7 +174,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let this = self.eval_context_ref();
         let os_str = this.read_os_str_from_c_str(ptr)?;
 
-        Ok(match this.convert_path_separator(Cow::Borrowed(os_str), PathConversion::TargetToHost) {
+        Ok(match this.convert_path(Cow::Borrowed(os_str), PathConversion::TargetToHost) {
             Cow::Borrowed(x) => Cow::Borrowed(Path::new(x)),
             Cow::Owned(y) => Cow::Owned(PathBuf::from(y)),
         })
@@ -188,10 +188,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let this = self.eval_context_ref();
         let os_str = this.read_os_str_from_wide_str(ptr)?;
 
-        Ok(this
-            .convert_path_separator(Cow::Owned(os_str), PathConversion::TargetToHost)
-            .into_owned()
-            .into())
+        Ok(this.convert_path(Cow::Owned(os_str), PathConversion::TargetToHost).into_owned().into())
     }
 
     /// Write a Path to the machine memory (as a null-terminated sequence of bytes),
@@ -203,8 +200,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         size: u64,
     ) -> InterpResult<'tcx, (bool, u64)> {
         let this = self.eval_context_mut();
-        let os_str = this
-            .convert_path_separator(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
+        let os_str =
+            this.convert_path(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
         this.write_os_str_to_c_str(&os_str, ptr, size)
     }
 
@@ -217,8 +214,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         size: u64,
     ) -> InterpResult<'tcx, (bool, u64)> {
         let this = self.eval_context_mut();
-        let os_str = this
-            .convert_path_separator(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
+        let os_str =
+            this.convert_path(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
         this.write_os_str_to_wide_str(&os_str, ptr, size)
     }
 
@@ -230,18 +227,19 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         memkind: MemoryKind<MiriMemoryKind>,
     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
         let this = self.eval_context_mut();
-        let os_str = this
-            .convert_path_separator(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
+        let os_str =
+            this.convert_path(Cow::Borrowed(path.as_os_str()), PathConversion::HostToTarget);
         this.alloc_os_str_as_c_str(&os_str, memkind)
     }
 
-    fn convert_path_separator<'a>(
+    fn convert_path<'a>(
         &self,
         os_str: Cow<'a, OsStr>,
         direction: PathConversion,
     ) -> Cow<'a, OsStr> {
         let this = self.eval_context_ref();
         let target_os = &this.tcx.sess.target.os;
+
         #[cfg(windows)]
         return if target_os == "windows" {
             // Windows-on-Windows, all fine.
@@ -252,10 +250,35 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 PathConversion::HostToTarget => ('\\', '/'),
                 PathConversion::TargetToHost => ('/', '\\'),
             };
-            let converted = os_str
+            let mut converted = os_str
                 .encode_wide()
                 .map(|wchar| if wchar == from as u16 { to as u16 } else { wchar })
                 .collect::<Vec<_>>();
+            // We also have to ensure that absolute paths remain absolute.
+            match direction {
+                PathConversion::HostToTarget => {
+                    // If this is an absolute Windows path that starts with a drive letter (`C:/...`
+                    // after separator conversion), it would not be considered absolute by Unix
+                    // target code.
+                    if converted.get(1).copied() == Some(':' as u16)
+                        && converted.get(2).copied() == Some('/' as u16)
+                    {
+                        // We add a `/` at the beginning, to store the absolute Windows
+                        // path in something that looks like an absolute Unix path.
+                        converted.insert(0, '/' as u16);
+                    }
+                }
+                PathConversion::TargetToHost => {
+                    // If the path is `\C:\`, the leading backslash was probably added by the above code
+                    // and we should get rid of it again.
+                    if converted.get(0).copied() == Some('\\' as u16)
+                        && converted.get(2).copied() == Some(':' as u16)
+                        && converted.get(3).copied() == Some('\\' as u16)
+                    {
+                        converted.remove(0);
+                    }
+                }
+            }
             Cow::Owned(OsString::from_wide(&converted))
         };
         #[cfg(unix)]
@@ -270,6 +293,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 .iter()
                 .map(|&wchar| if wchar == from as u8 { to as u8 } else { wchar })
                 .collect::<Vec<_>>();
+            // TODO: Once we actually support file system things on Windows targets, we'll probably
+            // have to also do something clever for absolute path preservation here, like above.
             Cow::Owned(OsString::from_vec(converted))
         } else {
             // Unix-on-Unix, all is fine.

src/shims/unix/fs.rs

@@ -1667,7 +1667,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 // 'readlink' truncates the resolved path if the provided buffer is not large
                 // enough, and does *not* add a null terminator. That means we cannot use the usual
                 // `write_path_to_c_str` and have to re-implement parts of it ourselves.
-                let resolved = this.convert_path_separator(
+                let resolved = this.convert_path(
                     Cow::Borrowed(resolved.as_ref()),
                     crate::shims::os_str::PathConversion::HostToTarget,
                 );

test-cargo-miri/src/main.rs

@@ -2,6 +2,7 @@ use byteorder::{BigEndian, ByteOrder};
 use std::env;
 #[cfg(unix)]
 use std::io::{self, BufRead};
+use std::path::PathBuf;
 
 fn main() {
     // Check env var set by `build.rs`.
@@ -21,12 +22,30 @@ fn main() {
     // If there were no arguments, access stdin and test working dir.
     // (We rely on the test runner to always disable isolation when passing no arguments.)
     if std::env::args().len() <= 1 {
+        fn host_to_target_path(path: String) -> PathBuf {
+            use std::ffi::{CStr, CString};
+
+            let path = CString::new(path).unwrap();
+            let mut out = Vec::with_capacity(1024);
+
+            unsafe {
+                extern "Rust" {
+                    fn miri_host_to_target_path(
+                        path: *const i8,
+                        out: *mut i8,
+                        out_size: usize,
+                    ) -> usize;
+                }
+                let ret = miri_host_to_target_path(path.as_ptr(), out.as_mut_ptr(), out.capacity());
+                assert_eq!(ret, 0);
+                let out = CStr::from_ptr(out.as_ptr()).to_str().unwrap();
+                PathBuf::from(out)
+            }
+        }
+
         // CWD should be crate root.
-        // We have to normalize slashes, as the env var might be set for a different target's conventions.
         let env_dir = env::current_dir().unwrap();
-        let env_dir = env_dir.to_string_lossy().replace("\\", "/");
-        let crate_dir = env::var_os("CARGO_MANIFEST_DIR").unwrap();
-        let crate_dir = crate_dir.to_string_lossy().replace("\\", "/");
+        let crate_dir = host_to_target_path(env::var("CARGO_MANIFEST_DIR").unwrap());
         assert_eq!(env_dir, crate_dir);
 
         #[cfg(unix)]

test-cargo-miri/subcrate/main.rs

@@ -4,13 +4,30 @@ use std::path::PathBuf;
 fn main() {
     println!("subcrate running");
 
+    fn host_to_target_path(path: String) -> PathBuf {
+        use std::ffi::{CStr, CString};
+
+        let path = CString::new(path).unwrap();
+        let mut out = Vec::with_capacity(1024);
+
+        unsafe {
+            extern "Rust" {
+                fn miri_host_to_target_path(
+                    path: *const i8,
+                    out: *mut i8,
+                    out_size: usize,
+                ) -> usize;
+            }
+            let ret = miri_host_to_target_path(path.as_ptr(), out.as_mut_ptr(), out.capacity());
+            assert_eq!(ret, 0);
+            let out = CStr::from_ptr(out.as_ptr()).to_str().unwrap();
+            PathBuf::from(out)
+        }
+    }
+
     // CWD should be workspace root, i.e., one level up from crate root.
-    // We have to normalize slashes, as the env var might be set for a different target's conventions.
     let env_dir = env::current_dir().unwrap();
-    let env_dir = env_dir.to_string_lossy().replace("\\", "/");
-    let crate_dir = env::var_os("CARGO_MANIFEST_DIR").unwrap();
-    let crate_dir = crate_dir.to_string_lossy().replace("\\", "/");
-    let crate_dir = PathBuf::from(crate_dir);
-    let crate_dir = crate_dir.parent().unwrap().to_string_lossy();
+    let crate_dir = host_to_target_path(env::var("CARGO_MANIFEST_DIR").unwrap());
+    let crate_dir = crate_dir.parent().unwrap();
     assert_eq!(env_dir, crate_dir);
 }

test-cargo-miri/subcrate/test.rs

@@ -1,16 +1,37 @@
 use std::env;
 
+use std::path::PathBuf;
+
 use byteorder::{ByteOrder, LittleEndian};
 
 fn main() {
     println!("subcrate testing");
 
+    fn host_to_target_path(path: String) -> PathBuf {
+        use std::ffi::{CStr, CString};
+
+        let path = CString::new(path).unwrap();
+        let mut out = Vec::with_capacity(1024);
+
+        unsafe {
+            extern "Rust" {
+                fn miri_host_to_target_path(
+                    path: *const i8,
+                    out: *mut i8,
+                    out_size: usize,
+                ) -> usize;
+            }
+            let ret = miri_host_to_target_path(path.as_ptr(), out.as_mut_ptr(), out.capacity());
+            assert_eq!(ret, 0);
+            let out = CStr::from_ptr(out.as_ptr()).to_str().unwrap();
+            PathBuf::from(out)
+        }
+    }
+
     // CWD should be crate root.
     // We have to normalize slashes, as the env var might be set for a different target's conventions.
     let env_dir = env::current_dir().unwrap();
-    let env_dir = env_dir.to_string_lossy().replace("\\", "/");
-    let crate_dir = env::var_os("CARGO_MANIFEST_DIR").unwrap();
-    let crate_dir = crate_dir.to_string_lossy().replace("\\", "/");
+    let crate_dir = host_to_target_path(env::var("CARGO_MANIFEST_DIR").unwrap());
     assert_eq!(env_dir, crate_dir);
 
     // Make sure we can call dev-dependencies.

tests/pass/shims/fs.rs

@@ -15,6 +15,7 @@ use std::io::{Error, ErrorKind, IsTerminal, Read, Result, Seek, SeekFrom, Write}
 use std::path::{Path, PathBuf};
 
 fn main() {
+    test_path_conversion();
     test_file();
     test_file_clone();
     test_file_create_new();
@@ -28,15 +29,11 @@ fn main() {
     test_directory();
     test_canonicalize();
     test_from_raw_os_error();
-    test_path_conversion();
 }
 
-fn tmp() -> PathBuf {
+fn host_to_target_path(path: String) -> PathBuf {
     use std::ffi::{CStr, CString};
 
-    let path = std::env::var("MIRI_TEMP")
-        .unwrap_or_else(|_| std::env::temp_dir().into_os_string().into_string().unwrap());
-    // These are host paths. We need to convert them to the target.
     let path = CString::new(path).unwrap();
     let mut out = Vec::with_capacity(1024);
 
@@ -51,6 +48,13 @@ fn tmp() -> PathBuf {
     }
 }
 
+fn tmp() -> PathBuf {
+    let path = std::env::var("MIRI_TEMP")
+        .unwrap_or_else(|_| std::env::temp_dir().into_os_string().into_string().unwrap());
+    // These are host paths. We need to convert them to the target.
+    host_to_target_path(path)
+}
+
 /// Prepare: compute filename and make sure the file does not exist.
 fn prepare(filename: &str) -> PathBuf {
     let path = tmp().join(filename);