Windows shims for env var emulation

Shims for GetEnvironmentVariableW / SetEnvironmentVariableW /
GetEnvironmentStringsW.
Passes test 'tests/run-pass/env.rs'

src/shims/env.rs

@@ -1,6 +1,7 @@
 use std::ffi::{OsString, OsStr};
 use std::env;
 use std::convert::TryFrom;
+use std::collections::hash_map::Values;
 
 use crate::stacked_borrows::Tag;
 use crate::rustc_target::abi::LayoutOf;
@@ -40,6 +41,10 @@ impl<'tcx> EnvVars<'tcx> {
         }
         ecx.update_environ()
     }
+
+    pub(super) fn values(&self) -> InterpResult<'tcx, Values<'_, OsString, Pointer<Tag>>> {
+        Ok(self.map.values())
+    }
 }
 
 fn alloc_env_var_as_c_str<'mir, 'tcx>(
@@ -82,6 +87,79 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         })
     }
 
+    fn getenvironmentvariablew(
+        &mut self,
+        name_op: OpTy<'tcx, Tag>, // LPCWSTR lpName
+        buf_op: OpTy<'tcx, Tag>, // LPWSTR  lpBuffer
+        size_op: OpTy<'tcx, Tag>, // DWORD   nSize
+    ) -> InterpResult<'tcx, u64> {
+        let this = self.eval_context_mut();
+        this.assert_target_os("windows", "GetEnvironmentVariableW");
+
+        let name_ptr = this.read_scalar(name_op)?.not_undef()?;
+        let name = this.read_os_str_from_wide_str(name_ptr)?;
+        Ok(match this.machine.env_vars.map.get(&name) {
+            Some(var_ptr) => {
+                // The offset is used to strip the "{name}=" part of the string.
+                let name_offset_bytes =
+                    u64::try_from(name.len()).unwrap().checked_add(1).unwrap().checked_mul(2).unwrap();
+                let var_ptr = Scalar::from(var_ptr.offset(Size::from_bytes(name_offset_bytes), this)?);
+
+                let var_size = u64::try_from(this.read_os_str_from_wide_str(var_ptr)?.len()).unwrap();
+                let buf_size = u64::try_from(this.read_scalar(size_op)?.to_i32()?).unwrap();
+                let return_val = if var_size.checked_add(1).unwrap() > buf_size {
+                    // If lpBuffer is not large enough to hold the data, the return value is the buffer size, in characters,
+                    // required to hold the string and its terminating null character and the contents of lpBuffer are undefined.
+                    var_size + 1
+                } else {
+                    let buf_ptr = this.read_scalar(buf_op)?.not_undef()?;
+                    for i in 0..var_size {
+                        this.memory.copy(
+                            this.force_ptr(var_ptr.ptr_offset(Size::from_bytes(i) * 2, this)?)?,
+                            this.force_ptr(buf_ptr.ptr_offset(Size::from_bytes(i) * 2, this)?)?,
+                            Size::from_bytes(2),
+                            true,
+                        )?;
+                    }
+                    // If the function succeeds, the return value is the number of characters stored in the buffer pointed to by lpBuffer,
+                    // not including the terminating null character.
+                    var_size
+                };
+                return_val
+            }
+            None => {
+                this.set_last_error(Scalar::from_u32(203))?; // ERROR_ENVVAR_NOT_FOUND
+                0 // return zero upon failure
+            }
+        })
+    }
+
+    fn getenvironmentstringsw(&mut self) -> InterpResult<'tcx, Scalar<Tag>> {
+        let this = self.eval_context_mut();
+        this.assert_target_os("windows", "GetEnvironmentStringsW");
+
+        // Info on layout of environment blocks in Windows: 
+        // https://docs.microsoft.com/en-us/windows/win32/procthread/environment-variables
+        let mut env_vars = std::ffi::OsString::new();
+        for &item in this.machine.env_vars.values()? {
+            let env_var = this.read_os_str_from_target_str(Scalar::from(item))?;
+            env_vars.push(env_var);
+            env_vars.push("\0");
+        }
+
+        // Allocate environment block
+        let tcx = this.tcx;
+        let env_block_size = env_vars.len().checked_add(1).unwrap();
+        let env_block_type = tcx.mk_array(tcx.types.u16, u64::try_from(env_block_size).unwrap());
+        let env_block_place = this.allocate(this.layout_of(env_block_type)?, MiriMemoryKind::WinHeap.into());
+
+        // Store environment variables to environment block
+        // Final null terminator(block terminator) is pushed by `write_os_str_to_wide_str`
+        this.write_os_str_to_wide_str(&env_vars, env_block_place, u64::try_from(env_block_size).unwrap())?;
+
+        Ok(env_block_place.ptr)
+    }
+
     fn setenv(
         &mut self,
         name_op: OpTy<'tcx, Tag>,
@@ -118,6 +196,46 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         }
     }
 
+    fn setenvironmentvariablew(
+        &mut self,
+        name_op: OpTy<'tcx, Tag>, // LPCWSTR lpName,
+        value_op: OpTy<'tcx, Tag>, // LPCWSTR lpValue,
+    ) -> InterpResult<'tcx, i32> {
+        let mut this = self.eval_context_mut();
+        this.assert_target_os("windows", "SetEnvironmentVariableW");
+
+        let name_ptr = this.read_scalar(name_op)?.not_undef()?;
+        let value_ptr = this.read_scalar(value_op)?.not_undef()?;
+
+        let mut new = None;
+        if !this.is_null(name_ptr)? {
+            let name = this.read_os_str_from_target_str(name_ptr)?;
+            if this.is_null(value_ptr)? {
+                // Delete environment variable `{name}`
+                if let Some(var) = this.machine.env_vars.map.remove(&name) {
+                    this.memory.deallocate(var, None, MiriMemoryKind::Machine.into())?;
+                    this.update_environ()?;
+                }
+                return Ok(1);  // return non-zero on success
+            }
+            if !name.is_empty() && !name.to_string_lossy().contains('=') {
+                let value = this.read_os_str_from_target_str(value_ptr)?;
+                new = Some((name.to_owned(), value.to_owned()));
+            }
+        }
+        if let Some((name, value)) = new {
+            let var_ptr = alloc_env_var_as_target_str(&name, &value, &mut this)?;
+            if let Some(var) = this.machine.env_vars.map.insert(name, var_ptr) {
+                this.memory
+                    .deallocate(var, None, MiriMemoryKind::Machine.into())?;
+            }
+            this.update_environ()?;
+            Ok(1) // return non-zero on success
+        } else {
+            Ok(0)
+        }
+    }
+
     fn unsetenv(&mut self, name_op: OpTy<'tcx, Tag>) -> InterpResult<'tcx, i32> {
         let this = self.eval_context_mut();
         let target_os = &this.tcx.sess.target.target.target_os;
@@ -126,7 +244,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let name_ptr = this.read_scalar(name_op)?.not_undef()?;
         let mut success = None;
         if !this.is_null(name_ptr)? {
-            let name = this.read_os_str_from_c_str(name_ptr)?.to_owned();
+            let name = this.read_os_str_from_target_str(name_ptr)?.to_owned();
             if !name.is_empty() && !name.to_string_lossy().contains('=') {
                 success = Some(this.machine.env_vars.map.remove(&name));
             }

src/shims/foreign_items/windows.rs

@@ -23,22 +23,26 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
             // Environment related shims
             "GetEnvironmentVariableW" => {
-                // args[0] : LPCWSTR lpName (32-bit ptr to a const string of 16-bit Unicode chars)
-                // args[1] : LPWSTR lpBuffer (32-bit pointer to a string of 16-bit Unicode chars)
-                // lpBuffer : ptr to buffer that receives contents of the env_var as a null-terminated string.
-                // Return `# of chars` stored in the buffer pointed to by lpBuffer, excluding null-terminator.
-                // Return 0 upon failure.
-
-                // This is not the env var you are looking for.
-                this.set_last_error(Scalar::from_u32(203))?; // ERROR_ENVVAR_NOT_FOUND
-                this.write_null(dest)?;
+                let result = this.getenvironmentvariablew(args[0], args[1], args[2])?;
+                this.write_scalar(Scalar::from_uint(result, dest.layout.size), dest)?;
             }
 
             "SetEnvironmentVariableW" => {
-                // args[0] : LPCWSTR lpName (32-bit ptr to a const string of 16-bit Unicode chars)
-                // args[1] : LPCWSTR lpValue (32-bit ptr to a const string of 16-bit Unicode chars)
-                // Return nonzero if success, else return 0.
-                throw_unsup_format!("can't set environment variable on Windows");
+                let result = this.setenvironmentvariablew(args[0], args[1])?;
+                this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
+            }
+
+            "GetEnvironmentStringsW" => {
+                let result = this.getenvironmentstringsw()?;
+                // If the function succeeds, the return value is a pointer to the environment block of the current process.
+                this.write_scalar(result, dest)?;
+            }
+
+            "FreeEnvironmentStringsW" => {
+                let old_vars_ptr = this.read_scalar(args[0])?.not_undef()?;
+                let result = this.memory.deallocate(this.force_ptr(old_vars_ptr)?, None, MiriMemoryKind::WinHeap.into()).is_ok();
+                // If the function succeeds, the return value is nonzero.
+                this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
             }
 
             // File related shims

tests/run-pass/env.rs

@@ -1,5 +1,3 @@
-//ignore-windows: TODO env var emulation stubbed out on Windows
-
 use std::env;
 
 fn main() {