Merge #1129

1129: Standard exception types for singlepass backend. r=losfair a=losfair



Co-authored-by: losfair <[email protected]>

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## **[Unreleased]**
 
+- [#1129](https://github.com/wasmerio/wasmer/pull/1129) Standard exception types for singlepass backend.
+
 ## 0.13.1 - 2020-01-16
 - Fix bug in wapm related to the `package.wasmer_extra_flags` entry in the manifest
 

lib/runtime-core/src/backend.rs

@@ -122,6 +122,32 @@ pub struct CompilerConfig {
     pub backend_specific_config: Option<BackendCompilerConfig>,
 }
 
+/// An exception table for a `RunnableModule`.
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
+pub struct ExceptionTable {
+    /// Mappings from offsets in generated machine code to the corresponding exception code.
+    pub offset_to_code: HashMap<usize, ExceptionCode>,
+}
+
+impl ExceptionTable {
+    pub fn new() -> Self {
+        Self::default()
+    }
+}
+
+/// The code of an exception.
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Serialize, Deserialize)]
+pub enum ExceptionCode {
+    /// An `unreachable` opcode was executed.
+    Unreachable,
+
+    /// An arithmetic exception, e.g. divided by zero.
+    Arithmetic,
+
+    /// Memory access exception, e.g. misaligned/out-of-bound read/write.
+    Memory,
+}
+
 pub trait Compiler {
     /// Compiles a `Module` from WebAssembly binary format.
     /// The `CompileToken` parameter ensures that this can only
@@ -153,6 +179,10 @@ pub trait RunnableModule: Send + Sync {
         None
     }
 
+    fn get_exception_table(&self) -> Option<&ExceptionTable> {
+        None
+    }
+
     unsafe fn patch_local_function(&self, _idx: usize, _target_address: usize) -> bool {
         false
     }

lib/runtime-core/src/error.rs

@@ -1,5 +1,6 @@
 //! The error module contains the data structures and helper functions used to implement errors that
 //! are produced and returned from the wasmer runtime core.
+use crate::backend::ExceptionCode;
 use crate::types::{FuncSig, GlobalDescriptor, MemoryDescriptor, TableDescriptor, Type};
 use core::borrow::Borrow;
 use std::any::Any;
@@ -208,6 +209,8 @@ impl std::fmt::Display for RuntimeError {
                     write!(f, "\"{}\"", s)
                 } else if let Some(s) = data.downcast_ref::<&str>() {
                     write!(f, "\"{}\"", s)
+                } else if let Some(exc_code) = data.downcast_ref::<ExceptionCode>() {
+                    write!(f, "Caught exception of type \"{:?}\".", exc_code)
                 } else {
                     write!(f, "unknown error")
                 }

lib/runtime-core/src/fault.rs

@@ -375,23 +375,50 @@ extern "C" fn signal_trap_handler(
                 _ => {}
             }
 
+            // Now we have looked up all possible handler tables but failed to find a handler
+            // for this exception that allows a normal return.
+            //
+            // So here we check whether this exception is caused by a suspend signal, return the
+            // state image if so, or throw the exception out otherwise.
+
             let ctx: &mut vm::Ctx = &mut **CURRENT_CTX.with(|x| x.get());
             let es_image = fault
                 .read_stack(None)
                 .expect("fault.read_stack() failed. Broken invariants?");
 
             if is_suspend_signal {
+                // If this is a suspend signal, we parse the runtime state and return the resulting image.
                 let image = build_instance_image(ctx, es_image);
                 unwind_result = Box::new(image);
             } else {
+                // Otherwise, this is a real exception and we just throw it to the caller.
                 if es_image.frames.len() > 0 {
                     eprintln!(
                         "\n{}",
                         "Wasmer encountered an error while running your WebAssembly program."
                     );
                     es_image.print_backtrace_if_needed();
                 }
-                // Just let the error propagate otherwise
+
+                // Look up the exception tables and try to find an exception code.
+                let exc_code = CURRENT_CODE_VERSIONS.with(|versions| {
+                    let versions = versions.borrow();
+                    for v in versions.iter() {
+                        if let Some(table) = v.runnable_module.get_exception_table() {
+                            let ip = fault.ip.get();
+                            let end = v.base + v.msm.total_size;
+                            if ip >= v.base && ip < end {
+                                if let Some(exc_code) = table.offset_to_code.get(&(ip - v.base)) {
+                                    return Some(*exc_code);
+                                }
+                            }
+                        }
+                    }
+                    None
+                });
+                if let Some(code) = exc_code {
+                    unwind_result = Box::new(code);
+                }
             }
 
             true

lib/runtime/src/lib.rs

@@ -94,7 +94,7 @@
 #[macro_use]
 extern crate serde_derive;
 
-pub use wasmer_runtime_core::backend::Features;
+pub use wasmer_runtime_core::backend::{ExceptionCode, Features};
 pub use wasmer_runtime_core::codegen::{MiddlewareChain, StreamingCompiler};
 pub use wasmer_runtime_core::export::Export;
 pub use wasmer_runtime_core::global::Global;
@@ -111,6 +111,12 @@ pub use wasmer_runtime_core::Func;
 pub use wasmer_runtime_core::{compile_with, validate};
 pub use wasmer_runtime_core::{func, imports};
 
+#[cfg(unix)]
+pub use wasmer_runtime_core::{
+    fault::{pop_code_version, push_code_version},
+    state::CodeVersion,
+};
+
 pub mod memory {
     //! The memory module contains the implementation data structures and helper functions used to
     //! manipulate and access wasm memory.