Add support for panicking in the emulated application when unsupported functionality is encountered

README.md

@@ -228,6 +228,11 @@ environment variable:
    This can be used to find which parts of your program are executing slowly under Miri.
    The profile is written out to a file with the prefix `<name>`, and can be processed
    using the tools in the repository https://github.com/rust-lang/measureme.
+* `-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 (and halting
+  execution). Note that code might not expect these operations to ever panic, so
+  this flag can lead to strange (mis)behavior.
 * `-Zmiri-seed=<hex>` configures the seed of the RNG that Miri uses to resolve
   non-determinism.  This RNG is used to pick base addresses for allocations.
   When isolation is enabled (the default), this is also used to emulate system

src/bin/miri.rs

@@ -296,6 +296,9 @@ fn main() {
                 "-Zmiri-ignore-leaks" => {
                     miri_config.ignore_leaks = true;
                 }
+                "-Zmiri-panic-on-unsupported" => {
+                    miri_config.panic_on_unsupported = true;
+                }
                 "-Zmiri-track-raw-pointers" => {
                     miri_config.track_raw = true;
                 }

src/eval.rs

@@ -59,6 +59,8 @@ pub struct MiriConfig {
     /// If `Some`, enable the `measureme` profiler, writing results to a file
     /// with the specified prefix.
     pub measureme_out: Option<String>,
+    /// Panic when unsupported functionality is encountered
+    pub panic_on_unsupported: bool,
 }
 
 impl Default for MiriConfig {
@@ -80,6 +82,7 @@ impl Default for MiriConfig {
             data_race_detector: true,
             cmpxchg_weak_failure_rate: 0.8,
             measureme_out: None,
+            panic_on_unsupported: false,
         }
     }
 }

src/helpers.rs

@@ -636,6 +636,23 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 == this.tcx.def_path(start_fn).krate
         })
     }
+
+    /// Handler that should be called when unsupported functionality is encountered.
+    /// This function will either panic within the context of the emulated application
+    /// or return an error in the Miri process context
+    ///
+    /// Return value of `Ok(bool)` indicates whether execution should continue.
+    fn handle_unsupported<S: AsRef<str>>(&mut self, error_msg: S) -> InterpResult<'tcx, ()> {
+        let this = self.eval_context_mut();
+        if this.machine.panic_on_unsupported {
+            // message is slightly different here to make automated analysis easier
+            let error_msg = format!("unsupported Miri functionality: {}", error_msg.as_ref());
+            this.start_panic(error_msg.as_ref(), StackPopUnwind::Skip)?;
+            return Ok(());
+        } else {
+            throw_unsup_format!("{}", error_msg.as_ref());
+        }
+    }
 }
 
 /// Check that the number of args is what we expect.

src/machine.rs

@@ -297,6 +297,11 @@ pub struct Evaluator<'mir, 'tcx> {
 
     /// Cache of `Instance` exported under the given `Symbol` name.
     pub(crate) exported_symbols_cache: FxHashMap<Symbol, Instance<'tcx>>,
+
+    /// Whether to raise a panic in the context of the evaluated process when unsupported
+    /// functionality is encountered. If `false`, an error is propagated in the Miri application context
+    /// instead (default behavior)
+    pub(crate) panic_on_unsupported: bool,
 }
 
 impl<'mir, 'tcx> Evaluator<'mir, 'tcx> {
@@ -326,6 +331,7 @@ impl<'mir, 'tcx> Evaluator<'mir, 'tcx> {
             profiler,
             string_cache: Default::default(),
             exported_symbols_cache: FxHashMap::default(),
+            panic_on_unsupported: config.panic_on_unsupported,
         }
     }
 }

src/shims/foreign_items.rs

@@ -259,7 +259,11 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                     if let Some(body) = this.lookup_exported_symbol(link_name_sym)? {
                         return Ok(Some(body));
                     }
-                    throw_unsup_format!("can't call (diverging) foreign function: {}", link_name);
+                    this.handle_unsupported(format!(
+                        "can't call (diverging) foreign function: {}",
+                        link_name
+                    ))?;
+                    return Ok(None);
                 }
             },
             Some(p) => p,
@@ -276,7 +280,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 if let Some(body) = this.lookup_exported_symbol(link_name_sym)? {
                     return Ok(Some(body));
                 }
-                throw_unsup_format!("can't call foreign function: {}", link_name);
+
+                this.handle_unsupported(format!("can't call foreign function: {}", link_name))?;
+                return Ok(None);
             }
         }
 

src/shims/panic.rs

@@ -161,7 +161,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         }
     }
 
-    /// Starta a panic in the interpreter with the given message as payload.
+    /// Start a panic in the interpreter with the given message as payload.
     fn start_panic(&mut self, msg: &str, unwind: StackPopUnwind) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
 

src/shims/posix/linux/foreign_items.rs

@@ -183,7 +183,10 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                     id if id == sys_futex => {
                         futex(this, args, dest)?;
                     }
-                    id => throw_unsup_format!("Miri does not support syscall ID {}", id),
+                    id => {
+                        this.handle_unsupported(format!("can't execute syscall with ID {}", id))?;
+                        return Ok(EmulateByNameResult::NotSupported);
+                    }
                 }
             }
 

src/shims/windows/foreign_items.rs

@@ -343,7 +343,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             // Better error for attempts to create a thread
             "CreateThread" => {
                 this.check_abi(abi, Abi::System { unwind: false })?;
-                throw_unsup_format!("Miri does not support concurrency on Windows");
+
+                this.handle_unsupported("can't create threads on Windows")?;
+                return Ok(EmulateByNameResult::AlreadyJumped);
             }
 
             // Incomplete shims that we "stub out" just to get pre-main initialization code to work.

tests/compile-fail/concurrency/thread-spawn.rs

@@ -3,7 +3,7 @@
 
 use std::thread;
 
-// error-pattern: Miri does not support concurrency on Windows
+// error-pattern: can't create threads on Windows
 
 fn main() {
     thread::spawn(|| {});

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