various small nits

- share implementation with miri_starting_unwind
- make test use a custom unwinding class
- extend comments
- use NeedsUnwind more consistently

Author: RalfJung

ci/ci.sh

@@ -145,7 +145,7 @@ case $HOST_TARGET in
     TEST_TARGET=s390x-unknown-linux-gnu run_tests # big-endian architecture of choice
     # Partially supported targets (tier 2)
     BASIC="empty_main integer vec string btreemap hello hashmap heap_alloc align" # ensures we have the basics: stdout/stderr, system allocator, randomness (for HashMap initialization)
-    UNIX="panic/panic concurrency/simple atomic libc-mem libc-misc libc-random env num_cpus" # the things that are very similar across all Unixes, and hence easily supported there
+    UNIX="panic/panic panic/unwind concurrency/simple atomic libc-mem libc-misc libc-random env num_cpus" # the things that are very similar across all Unixes, and hence easily supported there
     TEST_TARGET=x86_64-unknown-freebsd run_tests_minimal $BASIC $UNIX threadname libc-time fs
     TEST_TARGET=i686-unknown-freebsd   run_tests_minimal $BASIC $UNIX threadname libc-time fs
     TEST_TARGET=x86_64-unknown-illumos run_tests_minimal $BASIC $UNIX pthread-sync

src/intrinsics/atomic.rs

@@ -116,7 +116,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             _ => return Ok(EmulateItemResult::NotSupported),
         }
-        Ok(EmulateItemResult::NeedsJumping)
+        Ok(EmulateItemResult::NeedsReturn)
     }
 }
 

src/intrinsics/mod.rs

@@ -62,7 +62,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     args: instance.args,
                 }))
             }
-            EmulateItemResult::NeedsJumping => {
+            EmulateItemResult::NeedsReturn => {
                 trace!("{:?}", this.dump_place(&dest.clone().into()));
                 this.return_to_block(ret)?;
                 Ok(None)
@@ -446,6 +446,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             _ => return Ok(EmulateItemResult::NotSupported),
         }
 
-        Ok(EmulateItemResult::NeedsJumping)
+        Ok(EmulateItemResult::NeedsReturn)
     }
 }

src/intrinsics/simd.rs

@@ -746,7 +746,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             _ => return Ok(EmulateItemResult::NotSupported),
         }
-        Ok(EmulateItemResult::NeedsJumping)
+        Ok(EmulateItemResult::NeedsReturn)
     }
 
     fn fminmax_op(

src/shims/alloc.rs

@@ -87,7 +87,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
             AllocatorKind::Default => {
                 default(this)?;
-                Ok(EmulateItemResult::NeedsJumping)
+                Ok(EmulateItemResult::NeedsReturn)
             }
         }
     }

src/shims/foreign_items.rs

@@ -82,8 +82,8 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         }
 
         // The rest either implements the logic, or falls back to `lookup_exported_symbol`.
-        match this.emulate_foreign_item_inner(link_name, abi, args, dest, unwind)? {
-            EmulateItemResult::NeedsJumping => {
+        match this.emulate_foreign_item_inner(link_name, abi, args, dest)? {
+            EmulateItemResult::NeedsReturn => {
                 trace!("{:?}", this.dump_place(&dest.clone().into()));
                 this.return_to_block(ret)?;
             }
@@ -210,7 +210,6 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         abi: Abi,
         args: &[OpTy<'tcx, Provenance>],
         dest: &MPlaceTy<'tcx, Provenance>,
-        unwind: mir::UnwindAction,
     ) -> InterpResult<'tcx, EmulateItemResult> {
         let this = self.eval_context_mut();
 
@@ -222,7 +221,7 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             // by the specified `.so` file; we should continue and check if it corresponds to
             // a provided shim.
             if this.call_native_fn(link_name, dest, args)? {
-                return Ok(EmulateItemResult::NeedsJumping);
+                return Ok(EmulateItemResult::NeedsReturn);
             }
         }
 
@@ -267,9 +266,9 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         match link_name.as_str() {
             // Miri-specific extern functions
             "miri_start_unwind" => {
-                // `check_shim` happens inside `handle_miri_start_unwind`.
-                this.handle_miri_start_unwind(abi, link_name, args, unwind)?;
-                return Ok(EmulateItemResult::AlreadyJumped);
+                let [payload] = this.check_shim(abi, Abi::Rust, link_name, args)?;
+                this.handle_miri_start_unwind(payload)?;
+                return Ok(EmulateItemResult::NeedsUnwind);
             }
             "miri_run_provenance_gc" => {
                 let [] = this.check_shim(abi, Abi::Rust, link_name, args)?;
@@ -484,7 +483,7 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     "__rust_alloc" => return this.emulate_allocator(default),
                     "miri_alloc" => {
                         default(this)?;
-                        return Ok(EmulateItemResult::NeedsJumping);
+                        return Ok(EmulateItemResult::NeedsReturn);
                     }
                     _ => unreachable!(),
                 }
@@ -544,7 +543,7 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                     }
                     "miri_dealloc" => {
                         default(this)?;
-                        return Ok(EmulateItemResult::NeedsJumping);
+                        return Ok(EmulateItemResult::NeedsReturn);
                     }
                     _ => unreachable!(),
                 }
@@ -965,6 +964,6 @@ trait EvalContextExtPriv<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         };
         // We only fall through to here if we did *not* hit the `_` arm above,
         // i.e., if we actually emulated the function with one of the shims.
-        Ok(EmulateItemResult::NeedsJumping)
+        Ok(EmulateItemResult::NeedsReturn)
     }
 }

src/shims/mod.rs

@@ -22,10 +22,10 @@ pub use unix::{DirTable, FdTable};
 /// What needs to be done after emulating an item (a shim or an intrinsic) is done.
 pub enum EmulateItemResult {
     /// The caller is expected to jump to the return block.
-    NeedsJumping,
+    NeedsReturn,
     /// The caller is expected to jump to the unwind block.
     NeedsUnwind,
-    /// Jumping has already been taken care of.
+    /// Jumping to the next block has already been taken care of.
     AlreadyJumped,
     /// The item is not supported.
     NotSupported,

src/shims/panic.rs

@@ -13,7 +13,6 @@
 
 use rustc_ast::Mutability;
 use rustc_middle::{mir, ty};
-use rustc_span::Symbol;
 use rustc_target::spec::abi::Abi;
 use rustc_target::spec::PanicStrategy;
 
@@ -46,25 +45,15 @@ impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir,
 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     /// Handles the special `miri_start_unwind` intrinsic, which is called
     /// by libpanic_unwind to delegate the actual unwinding process to Miri.
-    fn handle_miri_start_unwind(
-        &mut self,
-        abi: Abi,
-        link_name: Symbol,
-        args: &[OpTy<'tcx, Provenance>],
-        unwind: mir::UnwindAction,
-    ) -> InterpResult<'tcx> {
+    fn handle_miri_start_unwind(&mut self, payload: &OpTy<'tcx, Provenance>) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
 
         trace!("miri_start_unwind: {:?}", this.frame().instance);
 
-        // Get the raw pointer stored in arg[0] (the panic payload).
-        let [payload] = this.check_shim(abi, Abi::Rust, link_name, args)?;
         let payload = this.read_scalar(payload)?;
         let thread = this.active_thread_mut();
         thread.panic_payloads.push(payload);
 
-        // Jump to the unwind block to begin unwinding.
-        this.unwind_to_block(unwind)?;
         Ok(())
     }
 

src/shims/unix/android/foreign_items.rs

@@ -27,6 +27,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
 
             _ => return Ok(EmulateItemResult::NotSupported),
         }
-        Ok(EmulateItemResult::NeedsJumping)
+        Ok(EmulateItemResult::NeedsReturn)
     }
 }

src/shims/unix/foreign_items.rs

@@ -640,14 +640,28 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
                 this.write_scalar(Scalar::from_target_usize(len, this), dest)?;
             }
             "_Unwind_RaiseException" => {
-                trace!("_Unwind_RaiseException: {:?}", this.frame().instance);
-
-                // Get the raw pointer stored in arg[0] (the panic payload).
+                // This is not formally part of POSIX, but it is very wide-spread on POSIX systems.
+                // It was originally specified as part of the Itanium C++ ABI:
+                // https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html#base-throw.
+                // On Linux it is
+                // documented as part of the LSB:
+                // https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/baselib--unwind-raiseexception.html
+                // Basically every other UNIX uses the exact same api though. Arm also references
+                // back to the Itanium C++ ABI for the definition of `_Unwind_RaiseException` for
+                // arm64:
+                // https://github.com/ARM-software/abi-aa/blob/main/cppabi64/cppabi64.rst#toc-entry-35
+                // For arm32 they did something custom, but similar enough that the same
+                // `_Unwind_RaiseException` impl in miri should work:
+                // https://github.com/ARM-software/abi-aa/blob/main/ehabi32/ehabi32.rst
+                if !matches!(&*this.tcx.sess.target.os, "linux" | "freebsd" | "illumos" | "solaris" | "android" | "macos") {
+                    throw_unsup_format!(
+                        "`_Unwind_RaiseException` is not supported on {}",
+                        this.tcx.sess.target.os
+                    );
+                }
+                // This function looks and behaves excatly like miri_start_unwind.
                 let [payload] = this.check_shim(abi, Abi::C { unwind: true }, link_name, args)?;
-                let payload = this.read_scalar(payload)?;
-                let thread = this.active_thread_mut();
-                thread.panic_payloads.push(payload);
-
+                this.handle_miri_start_unwind(payload)?;
                 return Ok(EmulateItemResult::NeedsUnwind);
             }
 
@@ -771,6 +785,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
             }
         };
 
-        Ok(EmulateItemResult::NeedsJumping)
+        Ok(EmulateItemResult::NeedsReturn)
     }
 }