addressing some of the PR comments; still issues with the TARGET env var

Author: Ellen Arteca

src/shims/foreign_items.rs

@@ -369,9 +369,12 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
 
         // First deal with any external C functions in linked .so file
         // (if any SO file is specified, and if the host target == the session target)
-        if this.machine.external_so_lib.as_ref().is_some()
-            && option_env!("TARGET") == Some(&this.tcx.sess.opts.target_triple.to_string())
-        {
+        if this.machine.external_so_lib.as_ref().is_some() {
+            if option_env!("TARGET") != Some(&this.tcx.sess.opts.target_triple.to_string()) {
+                throw_ub_format!(
+                    "calling external C functions in linked .so file requires target and host to be the same"
+                );
+            }
             // An Ok(false) here means that the function being called was not exported
             // by the specified SO file; we should continue and check if it corresponds to
             // a provided shim.

tests/compiletest.rs

@@ -12,15 +12,16 @@ fn miri_path() -> PathBuf {
 fn build_so_for_c_ffi_tests() {
     let cc = option_env!("CC").unwrap_or("cc");
     // Target directory that we can write to.
-    let so_target_dir = env!("CARGO_TARGET_DIR").to_owned() + "/miri-extern-so";
+    let so_target_dir = Path::new(&env::var_os("CARGO_TARGET_DIR").unwrap()).join("miri-extern-so");
     // Create the directory if it does not already exist.
-    std::fs::create_dir_all(so_target_dir.as_str())
+    std::fs::create_dir_all(&so_target_dir)
         .expect("Failed to create directory for shared object file");
+    let so_file_path = so_target_dir.join("libtestlib.so");
     let cc_output = Command::new(cc)
         .args([
             "-shared",
             "-o",
-            &(so_target_dir + "/libtestlib.so"),
+            so_file_path.to_str().unwrap(),
             "tests/extern-so/test.c",
             // Only add the functions specified in libcode.version to the shared object file.
             // This is to avoid automatically adding `malloc`, etc.

tests/fail/extern-so/function_not_in_SO.rs renamed to tests/fail/extern-so/function_not_in_so.rs

@@ -1,12 +1,12 @@
 error: unsupported operation: can't call foreign function: foo
-  --> $DIR/function_not_in_SO.rs:LL:CC
+  --> $DIR/function_not_in_so.rs:LL:CC
    |
 LL |         foo();
    |         ^^^^^ can't call foreign function: foo
    |
    = help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
    = note: backtrace:
-   = note: inside `main` at $DIR/function_not_in_SO.rs:LL:CC
+   = note: inside `main` at $DIR/function_not_in_so.rs:LL:CC
 
 note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace