Auto merge of #3950 - RalfJung:handle_unsupported_foreign_item, r=RalfJung,saethlin,oli-obk

remove -Zmiri-panic-on-unsupported flag

Fixes https://github.com/rust-lang/miri/issues/3952, see that issue for discussion.

11 files changed, 3 insertions, 69 deletions

diff --git a/src/tools/miri/README.md b/src/tools/miri/README.md
index 9a50079bc94..a73fefaaf34 100644
--- a/src/tools/miri/README.md
+++ b/src/tools/miri/README.md
@@ -392,11 +392,6 @@ to Miri failing to detect cases of undefined behavior in a program.
   but reports to the program that it did actually write. This is useful when you
   are not interested in the actual program's output, but only want to see Miri's
   errors and warnings.
-* `-Zmiri-panic-on-unsupported` will make 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-recursive-validation` is a *highly experimental* flag that makes validity checking
   recurse below references.
 * `-Zmiri-retag-fields[=<all|none|scalar>]` controls when Stacked Borrows retagging recurses into
diff --git a/src/tools/miri/src/bin/miri.rs b/src/tools/miri/src/bin/miri.rs
index 8d3ae97e0e9..717229ba8b3 100644
--- a/src/tools/miri/src/bin/miri.rs
+++ b/src/tools/miri/src/bin/miri.rs
@@ -530,8 +530,6 @@ fn main() {
         } else if arg == "-Zmiri-ignore-leaks" {
             miri_config.ignore_leaks = true;
             miri_config.collect_leak_backtraces = false;
-        } else if arg == "-Zmiri-panic-on-unsupported" {
-            miri_config.panic_on_unsupported = true;
         } else if arg == "-Zmiri-strict-provenance" {
             miri_config.provenance_mode = ProvenanceMode::Strict;
         } else if arg == "-Zmiri-permissive-provenance" {
diff --git a/src/tools/miri/src/eval.rs b/src/tools/miri/src/eval.rs
index ece76e581f2..75dce211dd4 100644
--- a/src/tools/miri/src/eval.rs
+++ b/src/tools/miri/src/eval.rs
@@ -129,8 +129,6 @@ 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,
     /// Which style to use for printing backtraces.
     pub backtrace_style: BacktraceStyle,
     /// Which provenance to use for int2ptr casts
@@ -183,7 +181,6 @@ impl Default for MiriConfig {
             track_outdated_loads: false,
             cmpxchg_weak_failure_rate: 0.8, // 80%
             measureme_out: None,
-            panic_on_unsupported: false,
             backtrace_style: BacktraceStyle::Short,
             provenance_mode: ProvenanceMode::Default,
             mute_stdout_stderr: false,
diff --git a/src/tools/miri/src/helpers.rs b/src/tools/miri/src/helpers.rs
index 013bfe03aaf..8bd429deefc 100644
--- a/src/tools/miri/src/helpers.rs
+++ b/src/tools/miri/src/helpers.rs
@@ -14,7 +14,6 @@ use rustc_index::IndexVec;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols::ExportedSymbol;
-use rustc_middle::mir;
 use rustc_middle::ty::layout::{FnAbiOf, LayoutOf, MaybeResult, TyAndLayout};
 use rustc_middle::ty::{self, FloatTy, IntTy, Ty, TyCtxt, UintTy};
 use rustc_session::config::CrateType;
@@ -949,21 +948,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         crate_name == "std" || crate_name == "std_miri_test"
     }
 
-    /// Handler that should be called when an unsupported foreign item is encountered.
-    /// This function will either panic within the context of the emulated application
-    /// or return an error in the Miri process context
-    fn handle_unsupported_foreign_item(&mut self, error_msg: String) -> 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}");
-            this.start_panic(error_msg.as_ref(), mir::UnwindAction::Continue)?;
-            interp_ok(())
-        } else {
-            throw_machine_stop!(TerminationInfo::UnsupportedForeignItem(error_msg));
-        }
-    }
-
     fn check_abi_and_shim_symbol_clash(
         &mut self,
         abi: Abi,
diff --git a/src/tools/miri/src/machine.rs b/src/tools/miri/src/machine.rs
index b9cebcfe9cd..0d28a4ed3e4 100644
--- a/src/tools/miri/src/machine.rs
+++ b/src/tools/miri/src/machine.rs
@@ -496,11 +496,6 @@ pub struct MiriMachine<'tcx> {
     /// `None` means no `Instance` exported under the given name is found.
     pub(crate) exported_symbols_cache: FxHashMap<Symbol, Option<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,
-
     /// Equivalent setting as RUST_BACKTRACE on encountering an error.
     pub(crate) backtrace_style: BacktraceStyle,
 
@@ -667,7 +662,6 @@ impl<'tcx> MiriMachine<'tcx> {
             profiler,
             string_cache: Default::default(),
             exported_symbols_cache: FxHashMap::default(),
-            panic_on_unsupported: config.panic_on_unsupported,
             backtrace_style: config.backtrace_style,
             local_crates,
             extern_statics: FxHashMap::default(),
@@ -807,7 +801,6 @@ impl VisitProvenance for MiriMachine<'_> {
             profiler: _,
             string_cache: _,
             exported_symbols_cache: _,
-            panic_on_unsupported: _,
             backtrace_style: _,
             local_crates: _,
             rng: _,
diff --git a/src/tools/miri/src/shims/foreign_items.rs b/src/tools/miri/src/shims/foreign_items.rs
index 78b07f68b44..7fce5b63306 100644
--- a/src/tools/miri/src/shims/foreign_items.rs
+++ b/src/tools/miri/src/shims/foreign_items.rs
@@ -83,11 +83,10 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     return interp_ok(Some(body));
                 }
 
-                this.handle_unsupported_foreign_item(format!(
+                throw_machine_stop!(TerminationInfo::UnsupportedForeignItem(format!(
                     "can't call foreign function `{link_name}` on OS `{os}`",
                     os = this.tcx.sess.target.os,
-                ))?;
-                return interp_ok(None);
+                )));
             }
         }
 
diff --git a/src/tools/miri/src/shims/unix/linux/foreign_items.rs b/src/tools/miri/src/shims/unix/linux/foreign_items.rs
index 2a72004378e..2f3e1f29dd2 100644
--- a/src/tools/miri/src/shims/unix/linux/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/linux/foreign_items.rs
@@ -168,10 +168,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                         this.write_int(result.to_i32()?, dest)?;
                     }
                     id => {
-                        this.handle_unsupported_foreign_item(format!(
-                            "can't execute syscall with ID {id}"
-                        ))?;
-                        return interp_ok(EmulateItemResult::AlreadyJumped);
+                        throw_unsup_format!("can't execute syscall with ID {id}");
                     }
                 }
             }
diff --git a/src/tools/miri/tests/panic/unsupported_foreign_function.rs b/src/tools/miri/tests/panic/unsupported_foreign_function.rs
deleted file mode 100644
index b8301c50772..00000000000
--- a/src/tools/miri/tests/panic/unsupported_foreign_function.rs
+++ /dev/null
@@ -1,12 +0,0 @@
-//@compile-flags: -Zmiri-panic-on-unsupported
-//@normalize-stderr-test: "OS `.*`" -> "$$OS"
-
-fn main() {
-    extern "Rust" {
-        fn foo();
-    }
-
-    unsafe {
-        foo();
-    }
-}
diff --git a/src/tools/miri/tests/panic/unsupported_foreign_function.stderr b/src/tools/miri/tests/panic/unsupported_foreign_function.stderr
deleted file mode 100644
index 278af9612d6..00000000000
--- a/src/tools/miri/tests/panic/unsupported_foreign_function.stderr
+++ /dev/null
@@ -1,4 +0,0 @@
-thread 'main' panicked at tests/panic/unsupported_foreign_function.rs:LL:CC:
-unsupported Miri functionality: can't call foreign function `foo` on $OS
-note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
diff --git a/src/tools/miri/tests/panic/unsupported_syscall.rs b/src/tools/miri/tests/panic/unsupported_syscall.rs
deleted file mode 100644
index bbb076b169a..00000000000
--- a/src/tools/miri/tests/panic/unsupported_syscall.rs
+++ /dev/null
@@ -1,9 +0,0 @@
-//@ignore-target: windows # no `syscall` on Windows
-//@ignore-target: apple # `syscall` is not supported on macOS
-//@compile-flags: -Zmiri-panic-on-unsupported
-
-fn main() {
-    unsafe {
-        libc::syscall(0);
-    }
-}
diff --git a/src/tools/miri/tests/panic/unsupported_syscall.stderr b/src/tools/miri/tests/panic/unsupported_syscall.stderr
deleted file mode 100644
index e9b2b5b6652..00000000000
--- a/src/tools/miri/tests/panic/unsupported_syscall.stderr
+++ /dev/null
@@ -1,4 +0,0 @@
-thread 'main' panicked at tests/panic/unsupported_syscall.rs:LL:CC:
-unsupported Miri functionality: can't execute syscall with ID 0
-note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
-note: in Miri, you may have to set `MIRIFLAGS=-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect