remove the ability to disable ABI checking

Author: RalfJung

README.md

@@ -359,8 +359,6 @@ The remaining flags are for advanced use only, and more likely to change or be r
 Some of these are **unsound**, which means they can lead
 to Miri failing to detect cases of undefined behavior in a program.
 
-* `-Zmiri-disable-abi-check` disables checking [function ABI]. Using this flag
-  is **unsound**. This flag is **deprecated**.
 * `-Zmiri-disable-alignment-check` disables checking pointer alignment, so you
   can focus on other failures, but it means Miri can miss bugs in your program.
   Using this flag is **unsound**.

src/bin/miri.rs

@@ -413,10 +413,9 @@ fn main() {
             );
         } else if arg == "-Zmiri-disable-abi-check" {
             eprintln!(
-                "WARNING: the flag `-Zmiri-disable-abi-check` is deprecated and planned to be removed.\n\
-                If you have a use-case for it, please file an issue."
+                "WARNING: the flag `-Zmiri-disable-abi-check` no longer has any effect; \
+                    ABI checks cannot be disabled any more"
             );
-            miri_config.check_abi = false;
         } else if arg == "-Zmiri-disable-isolation" {
             if matches!(isolation_enabled, Some(true)) {
                 show_error!(

src/eval.rs

@@ -94,8 +94,6 @@ pub struct MiriConfig {
     pub unique_is_unique: bool,
     /// Controls alignment checking.
     pub check_alignment: AlignmentCheck,
-    /// Controls function [ABI](Abi) checking.
-    pub check_abi: bool,
     /// Action for an op requiring communication with the host.
     pub isolated_op: IsolatedOp,
     /// Determines if memory leaks should be ignored.
@@ -160,7 +158,6 @@ impl Default for MiriConfig {
             borrow_tracker: Some(BorrowTrackerMethod::StackedBorrows),
             unique_is_unique: false,
             check_alignment: AlignmentCheck::Int,
-            check_abi: true,
             isolated_op: IsolatedOp::Reject(RejectOpWith::Abort),
             ignore_leaks: false,
             forwarded_env_vars: vec![],

src/helpers.rs

@@ -380,7 +380,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let this = self.eval_context_mut();
         let param_env = ty::ParamEnv::reveal_all(); // in Miri this is always the param_env we use... and this.param_env is private.
         let callee_abi = f.ty(*this.tcx, param_env).fn_sig(*this.tcx).abi();
-        if this.machine.enforce_abi && callee_abi != caller_abi {
+        if callee_abi != caller_abi {
             throw_ub_format!(
                 "calling a function with ABI {} using caller ABI {}",
                 callee_abi.name(),
@@ -938,7 +938,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
     /// Check that the ABI is what we expect.
     fn check_abi<'a>(&self, abi: Abi, exp_abi: Abi) -> InterpResult<'a, ()> {
-        if self.eval_context_ref().machine.enforce_abi && abi != exp_abi {
+        if abi != exp_abi {
             throw_ub_format!(
                 "calling a function with ABI {} using caller ABI {}",
                 exp_abi.name(),

src/machine.rs

@@ -460,9 +460,6 @@ pub struct MiriMachine<'mir, 'tcx> {
     /// Whether to enforce the validity invariant.
     pub(crate) validate: bool,
 
-    /// Whether to enforce [ABI](Abi) of function calls.
-    pub(crate) enforce_abi: bool,
-
     /// The table of file descriptors.
     pub(crate) file_handler: shims::unix::FileHandler,
     /// The table of directory descriptors.
@@ -639,7 +636,6 @@ impl<'mir, 'tcx> MiriMachine<'mir, 'tcx> {
             tls: TlsData::default(),
             isolated_op: config.isolated_op,
             validate: config.validate,
-            enforce_abi: config.check_abi,
             file_handler: FileHandler::new(config.mute_stdout_stderr),
             dir_handler: Default::default(),
             layouts,
@@ -781,7 +777,6 @@ impl VisitProvenance for MiriMachine<'_, '_> {
             tcx: _,
             isolated_op: _,
             validate: _,
-            enforce_abi: _,
             clock: _,
             layouts: _,
             static_roots: _,
@@ -928,8 +923,8 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     }
 
     #[inline(always)]
-    fn enforce_abi(ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
-        ecx.machine.enforce_abi
+    fn enforce_abi(_ecx: &MiriInterpCx<'mir, 'tcx>) -> bool {
+        true
     }
 
     #[inline(always)]

tests/fail-dep/concurrency/unwind_top_of_stack.rs

@@ -19,7 +19,6 @@ fn main() {
         after_call = {
             Return()
         }
-
     }
 }
 

tests/fail-dep/concurrency/unwind_top_of_stack.stderr

@@ -1,4 +1,3 @@
-//@compile-flags: -Zmiri-disable-abi-check
 #![feature(c_unwind)]
 
 #[no_mangle]

tests/fail/function_calls/arg_inplace_mutate.rs

@@ -1,5 +1,3 @@
-WARNING: the flag `-Zmiri-disable-abi-check` is deprecated and planned to be removed.
-If you have a use-case for it, please file an issue.
 thread 'main' panicked at $DIR/exported_symbol_bad_unwind1.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

tests/fail/function_calls/exported_symbol_bad_unwind1.rs

@@ -1,6 +1,9 @@
 #![feature(c_unwind)]
 
 //! Unwinding when the caller ABI is "C" (without "-unwind") is UB.
+// The opposite version (callee does not allow unwinding) is impossible to
+// even write: MIR validation catches functions that have `UnwindContinue` but
+// are not allowed to unwind.
 
 extern "C-unwind" fn unwind() {
     panic!();