add working shim for environ

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

@@ -84,6 +84,9 @@ pub struct MemoryExtra {
     /// An allocation ID to report when it is being allocated
     /// (helps for debugging memory leaks).
     tracked_alloc_id: Option<AllocId>,
+
+    /// The `AllocId` for the `environ` static.
+    pub(crate) environ: Option<Scalar<Tag>>,
 }
 
 impl MemoryExtra {
@@ -99,6 +102,7 @@ impl MemoryExtra {
             extern_statics: FxHashMap::default(),
             rng: RefCell::new(rng),
             tracked_alloc_id,
+            environ: None,
         }
     }
 
@@ -118,6 +122,16 @@ impl MemoryExtra {
                     .extern_statics
                     .insert(Symbol::intern("__cxa_thread_atexit_impl"), place.ptr.assert_ptr().alloc_id)
                     .unwrap_none();
+
+                // "environ"
+                let layout = this.layout_of(this.tcx.types.usize)?;
+                let place = this.allocate(layout, MiriMemoryKind::Machine.into());
+                this.write_scalar(this.memory.extra.environ.unwrap(), place.into())?;
+                this.memory
+                    .extra
+                    .extern_statics
+                    .insert(Symbol::intern("environ"), place.ptr.assert_ptr().alloc_id)
+                    .unwrap_none();
             }
             _ => {} // No "extern statics" supported on this platform
         }

src/shims/env.rs

@@ -2,6 +2,7 @@ use std::ffi::{OsString, OsStr};
 use std::env;
 
 use crate::stacked_borrows::Tag;
+use crate::rustc_target::abi::LayoutOf;
 use crate::*;
 
 use rustc_data_structures::fx::FxHashMap;
@@ -20,15 +21,29 @@ impl EnvVars {
         ecx: &mut InterpCx<'mir, 'tcx, Evaluator<'tcx>>,
         excluded_env_vars: Vec<String>,
     ) {
+        let mut vars = Vec::new();
         if ecx.machine.communicate {
             for (name, value) in env::vars() {
                 if !excluded_env_vars.contains(&name) {
                     let var_ptr =
                         alloc_env_var_as_c_str(name.as_ref(), value.as_ref(), ecx);
                     ecx.machine.env_vars.map.insert(OsString::from(name), var_ptr);
+                    vars.push(var_ptr.into());
                 }
             }
         }
+        // Add the trailing null pointer
+        vars.push(Scalar::from_int(0, ecx.pointer_size()));
+        // Make an array with all these pointers inside Miri.
+        let tcx = ecx.tcx;
+        let environ_layout =
+            ecx.layout_of(tcx.mk_array(tcx.mk_imm_ptr(tcx.types.u8), vars.len() as u64)).unwrap();
+        let environ_place = ecx.allocate(environ_layout, MiriMemoryKind::Machine.into());
+        for (idx, var) in vars.into_iter().enumerate() {
+            let place = ecx.mplace_field(environ_place, idx as u64).unwrap();
+            ecx.write_scalar(var, place.into()).unwrap();
+        }
+        ecx.memory.extra.environ = Some(environ_place.ptr.into());
     }
 }