From 76d99c37c90496425fb7f3f8e2be4e9c16f276af Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sat, 6 Aug 2022 15:21:08 -0400
Subject: [PATCH] fix RUSTC_BACKTRACE always being set

---
 src/bin/miri.rs  | 7 +++++++
 src/eval.rs      | 6 +++++-
 src/shims/env.rs | 8 ++++----
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/bin/miri.rs b/src/bin/miri.rs
index 489eb959906..430f9e2f637 100644
--- a/src/bin/miri.rs
+++ b/src/bin/miri.rs
@@ -306,6 +306,11 @@ fn parse_comma_list<T: FromStr>(input: &str) -> Result<Vec<T>, T::Err> {
 }
 
 fn main() {
+    // Snapshot a copy of the environment before `rustc` starts messing with it.
+    // (`install_ice_hook` might change `RUST_BACKTRACE`.)
+    let env_snapshot = env::vars_os().collect::<Vec<_>>();
+
+    // Earliest rustc setup.
     rustc_driver::install_ice_hook();
 
     // If the environment asks us to actually be rustc, then do that.
@@ -333,6 +338,8 @@ fn main() {
 
     // Parse our arguments and split them across `rustc` and `miri`.
     let mut miri_config = miri::MiriConfig::default();
+    miri_config.env = env_snapshot;
+
     let mut rustc_args = vec![];
     let mut after_dashdash = false;
 
diff --git a/src/eval.rs b/src/eval.rs
index cb24dea3a88..981776e3eeb 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -1,7 +1,7 @@
 //! Main evaluator loop and setting up the initial stack frame.
 
 use std::collections::HashSet;
-use std::ffi::OsStr;
+use std::ffi::{OsStr, OsString};
 use std::iter;
 use std::panic::{self, AssertUnwindSafe};
 use std::thread;
@@ -72,6 +72,9 @@ pub enum BacktraceStyle {
 /// Configuration needed to spawn a Miri instance.
 #[derive(Clone)]
 pub struct MiriConfig {
+    /// The host environment snapshot to use as basis for what is provided to the interpreted program.
+    /// (This is still subject to isolation as well as `excluded_env_vars` and `forwarded_env_vars`.)
+    pub env: Vec<(OsString, OsString)>,
     /// Determine if validity checking is enabled.
     pub validate: bool,
     /// Determines if Stacked Borrows is enabled.
@@ -130,6 +133,7 @@ pub struct MiriConfig {
 impl Default for MiriConfig {
     fn default() -> MiriConfig {
         MiriConfig {
+            env: vec![],
             validate: true,
             stacked_borrows: true,
             check_alignment: AlignmentCheck::Int,
diff --git a/src/shims/env.rs b/src/shims/env.rs
index db1ddf6291f..07b9cf18192 100644
--- a/src/shims/env.rs
+++ b/src/shims/env.rs
@@ -49,11 +49,11 @@ pub(crate) fn init<'mir>(
 
         // Skip the loop entirely if we don't want to forward anything.
         if ecx.machine.communicate() || !config.forwarded_env_vars.is_empty() {
-            for (name, value) in env::vars_os() {
+            for (name, value) in &config.env {
                 // Always forward what is in `forwarded_env_vars`; that list can take precedence over excluded_env_vars.
-                let forward = config.forwarded_env_vars.iter().any(|v| **v == name)
+                let forward = config.forwarded_env_vars.iter().any(|v| **v == *name)
                     || (ecx.machine.communicate()
-                        && !excluded_env_vars.iter().any(|v| **v == name));
+                        && !excluded_env_vars.iter().any(|v| **v == *name));
                 if forward {
                     let var_ptr = match target_os {
                         target if target_os_is_unix(target) =>
@@ -65,7 +65,7 @@ pub(crate) fn init<'mir>(
                                 unsupported
                             ),
                     };
-                    ecx.machine.env_vars.map.insert(name, var_ptr);
+                    ecx.machine.env_vars.map.insert(name.clone(), var_ptr);
                 }
             }
         }