only expose environ on linux

Author: pvdrz

src/eval.rs

@@ -77,8 +77,8 @@ pub fn create_ecx<'mir, 'tcx: 'mir>(
         ),
     );
     // Complete initialization.
-    MemoryExtra::init_extern_statics(&mut ecx)?;
     EnvVars::init(&mut ecx, config.excluded_env_vars)?;
+    MemoryExtra::init_extern_statics(&mut ecx)?;
 
     // Setup first stack-frame
     let main_instance = ty::Instance::mono(tcx, main_id);

src/machine.rs

@@ -112,29 +112,23 @@ impl<'tcx> MemoryExtra<'tcx> {
     ) -> InterpResult<'tcx> {
         let target_os = this.tcx.sess.target.target.target_os.as_str();
         match target_os {
-            "linux" | "macos" => {
-                if target_os == "linux" {
-                    // "__cxa_thread_atexit_impl"
-                    // This should be all-zero, pointer-sized.
-                    let layout = this.layout_of(this.tcx.types.usize)?;
-                    let place = this.allocate(layout, MiriMemoryKind::Machine.into());
-                    this.write_scalar(Scalar::from_machine_usize(0, &*this.tcx), place.into())?;
-                    this.memory
-                        .extra
-                        .extern_statics
-                        .insert(Symbol::intern("__cxa_thread_atexit_impl"), place.ptr.assert_ptr().alloc_id)
-                        .unwrap_none();
-                }
-                // "environ"
+            "linux" => {
+                // "__cxa_thread_atexit_impl"
+                // This should be all-zero, pointer-sized.
                 let layout = this.layout_of(this.tcx.types.usize)?;
                 let place = this.allocate(layout, MiriMemoryKind::Machine.into());
                 this.write_scalar(Scalar::from_machine_usize(0, &*this.tcx), place.into())?;
                 this.memory
                     .extra
                     .extern_statics
-                    .insert(Symbol::intern("environ"), place.ptr.assert_ptr().alloc_id)
+                    .insert(Symbol::intern("__cxa_thread_atexit_impl"), place.ptr.assert_ptr().alloc_id)
+                    .unwrap_none();
+                // "environ"
+                this.memory
+                    .extra
+                    .extern_statics
+                    .insert(Symbol::intern("environ"), this.memory.extra.environ.unwrap().ptr.assert_ptr().alloc_id)
                     .unwrap_none();
-                this.memory.extra.environ = Some(place);
             }
             _ => {} // No "extern statics" supported on this platform
         }

src/shims/env.rs

@@ -30,6 +30,11 @@ impl EnvVars {
                 }
             }
         }
+        // Initialize the `environ` static
+        let layout = ecx.layout_of(ecx.tcx.types.usize)?;
+        let place = ecx.allocate(layout, MiriMemoryKind::Machine.into());
+        ecx.write_scalar(Scalar::from_machine_usize(0, &*ecx.tcx), place.into())?;
+        ecx.memory.extra.environ = Some(place);
         ecx.update_environ()
     }
 }
@@ -156,12 +161,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
     }
 
     /// Updates the `environ` static. It should not be called before
-    /// `MemoryExtra::init_extern_statics`.
+    /// `EnvVars::init`.
     fn update_environ(&mut self) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
         // Deallocate the old environ value.
         let old_vars_ptr = this.read_scalar(this.memory.extra.environ.unwrap().into())?.not_undef()?;
-        // The pointer itself can be null because `MemoryExtra::init_extern_statics` only
+        // The pointer itself can be null because `EnvVars::init` only
         // initializes the place for the static but not the static itself.
         if !this.is_null(old_vars_ptr)? {
             this.memory.deallocate(this.force_ptr(old_vars_ptr)?, None, MiriMemoryKind::Machine.into())?;

src/shims/foreign_items/posix/macos.rs

@@ -41,10 +41,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let result = this.macos_fstat(args[0], args[1])?;
                 this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
             }
-            // Environment related shims
-            "_NSGetEnviron" => {
-                this.write_scalar(this.memory.extra.environ.unwrap().ptr, dest)?;
-            }
+
             // The only reason this is not in the `posix` module is because the `linux` item has a
             // different name.
             "opendir$INODE64" => {
@@ -59,6 +56,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 this.write_scalar(Scalar::from_int(result, dest.layout.size), dest)?;
             }
 
+            // Environment related shims
+            "_NSGetEnviron" => {
+                this.write_scalar(this.memory.extra.environ.unwrap().ptr, dest)?;
+            }
+
             // Time related shims
             "gettimeofday" => {
                 let result = this.gettimeofday(args[0], args[1])?;

tests/compile-fail/environ-gets-deallocated.rs

@@ -3,9 +3,9 @@
 #[cfg(target_os="linux")]
 fn get_environ() -> *const *const u8 {
   extern "C" {
-    static environ: *const *const u8;
+    static mut environ: *const *const u8;
   }
-  environ
+  unsafe { environ }
 }
 
 #[cfg(target_os="macos")]