PR edits: check for host == target, moving some testing setup around as per @RalfJung s comments

Author: Ellen Arteca

miri

@@ -104,7 +104,8 @@ esac
 
 ## Prepare the environment
 # Determine some toolchain properties
-TARGET=$(rustc +$TOOLCHAIN --version --verbose | grep "^host:" | cut -d ' ' -f 2)
+# export the target so its available in miri
+export TARGET=$(rustc +$TOOLCHAIN --version --verbose | grep "^host:" | cut -d ' ' -f 2)
 SYSROOT=$(rustc +$TOOLCHAIN --print sysroot)
 LIBDIR=$SYSROOT/lib/rustlib/$TARGET/lib
 if ! test -d "$LIBDIR"; then

src/shims/ffi_support.rs

@@ -237,8 +237,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             .map(|cur_arg| cur_arg.arg_downcast())
             .collect::<Vec<libffi::high::Arg<'_>>>();
 
-        // Code pointer to C function.
-        // let ptr = CodePtr(*func.deref() as *mut _);
         // Call the function and store output, depending on return type in the function signature.
         self.call_external_c_and_store_return(link_name, dest, code_ptr, libffi_args)?;
         Ok(true)
@@ -272,7 +270,7 @@ pub enum CArg {
 
 impl<'a> CArg {
     /// Convert a `CArg` to a `libffi` argument type.
-    pub fn arg_downcast(&'a self) -> libffi::high::Arg<'a> {
+    fn arg_downcast(&'a self) -> libffi::high::Arg<'a> {
         match self {
             CArg::Int8(i) => ffi::arg(i),
             CArg::Int16(i) => ffi::arg(i),

src/shims/foreign_items.rs

@@ -368,8 +368,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let this = self.eval_context_mut();
 
         // First deal with any external C functions in linked .so file
-        // (if any SO file is specified).
-        if this.machine.external_so_lib.as_ref().is_some() {
+        // (if any SO file is specified, and if the host target == the session target)
+        if this.machine.external_so_lib.as_ref().is_some()
+            && env!("TARGET") == this.tcx.sess.opts.target_triple.to_string()
+        {
             // 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

@@ -11,11 +11,16 @@ fn miri_path() -> PathBuf {
 // Build the shared object file for testing external C function calls.
 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";
+    // Create the directory if it does not already exist.
+    std::fs::create_dir_all(so_target_dir.as_str())
+        .expect("Failed to create directory for shared object file");
     let cc_output = Command::new(cc)
         .args([
             "-shared",
             "-o",
-            "tests/extern-so/libtestlib.so",
+            &(so_target_dir + "/libtestlib.so"),
             "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.