Update README, add tests

Author: landaire

README.md

@@ -262,6 +262,9 @@ environment variable:
   this pointer. Note that it is not currently guaranteed that code that works
   with `-Zmiri-track-raw-pointers` also works without
   `-Zmiri-track-raw-pointers`, but for the vast majority of code, this will be the case.
+* `-Zmiri-panic-on-unsupported` will makes some forms of unsupported functionality
+  such as FFI and unsupported syscalls panic within the context of the emulated
+  application instead of raising an error within the context of Miri.
 
 Some native rustc `-Z` flags are also very relevant for Miri:
 

src/bin/miri.rs

@@ -233,7 +233,7 @@ fn main() {
                 "-Zmiri-ignore-leaks" => {
                     miri_config.ignore_leaks = true;
                 }
-                "-Zmiri-panic-on-unsupported-syscalls" => {
+                "-Zmiri-panic-on-unsupported" => {
                     miri_config.panic_on_unsupported = true;
                 }
                 "-Zmiri-track-raw-pointers" => {

src/shims/posix/linux/foreign_items.rs

@@ -189,7 +189,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                         );
                         if this.eval_context_ref().machine.panic_on_unsupported {
                             // message is slightly different here to make automated analysis easier
-                            this.start_panic(error_msg.as_ref(), StackPopUnwind::NotAllowed)?;
+                            this.start_panic(error_msg.as_ref(), StackPopUnwind::Skip)?;
                             return Ok(false);
                         } else {
                             throw_unsup_format!("{}", error_msg);
@@ -233,7 +233,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 );
                 if this.eval_context_ref().machine.panic_on_unsupported {
                     // message is slightly different here to make automated analysis easier
-                    this.start_panic(error_msg.as_ref(), StackPopUnwind::NotAllowed)?;
+                    this.start_panic(error_msg.as_ref(), StackPopUnwind::Skip)?;
                     return Ok(false);
                 } else {
                     throw_unsup_format!("{}", error_msg);

src/shims/posix/macos/foreign_items.rs

@@ -163,7 +163,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 );
                 if this.eval_context_ref().machine.panic_on_unsupported {
                     // message is slightly different here to make automated analysis easier
-                    this.start_panic(error_msg.as_ref(), StackPopUnwind::NotAllowed)?;
+                    this.start_panic(error_msg.as_ref(), StackPopUnwind::Skip)?;
                     return Ok(false);
                 } else {
                     throw_unsup_format!("{}", error_msg);

src/shims/windows/foreign_items.rs

@@ -346,7 +346,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let error_msg =
                     "unsupported Miri functionality: concurrency is not supported on Windows";
                 if this.eval_context_ref().machine.panic_on_unsupported {
-                    this.start_panic(error_msg, StackPopUnwind::NotAllowed)?;
+                    this.start_panic(error_msg, StackPopUnwind::Skip)?;
                     return Ok(false);
                 } else {
                     throw_unsup_format!("{}", error_msg);
@@ -430,7 +430,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 );
                 if this.eval_context_ref().machine.panic_on_unsupported {
                     // message is slightly different here to make automated analysis easier
-                    this.start_panic(error_msg.as_ref(), StackPopUnwind::NotAllowed)?;
+                    this.start_panic(error_msg.as_ref(), StackPopUnwind::Skip)?;
                     return Ok(false);
                 } else {
                     throw_unsup_format!("{}", error_msg);

tests/compile-fail/unsupported_foreign_function.rs

@@ -4,6 +4,6 @@ fn main() {
     }
 
     unsafe {
-        foo(); //~ ERROR unsupported operation: can't call foreign function: foo
+        foo(); //~ ERROR unsupported Miri functionality: can't call foreign function "foo"
     }
 }

tests/run-pass/panic/unsupported_foreign_function.rs

@@ -0,0 +1,11 @@
+// compile-flags: -Zmiri-panic-on-unsupported
+
+fn main() {
+    extern "Rust" {
+        fn foo();
+    }
+
+    unsafe {
+        foo();
+    }
+}

tests/run-pass/panic/unsupported_foreign_function.stderr

@@ -0,0 +1,2 @@
+thread 'main' panicked at 'unsupported Miri functionality: can't call foreign function "foo"', $DIR/unsupported_foreign_function.rs:9:9
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace