Polymorphic host functions based on dynamic trampoline generation.

lib/runtime-core-tests/tests/imports.rs

@@ -1,6 +1,13 @@
+use std::sync::Arc;
 use wasmer_runtime_core::{
-    compile_with, error::RuntimeError, imports, memory::Memory, typed_func::Func,
-    types::MemoryDescriptor, units::Pages, vm, Instance,
+    compile_with,
+    error::RuntimeError,
+    imports,
+    memory::Memory,
+    typed_func::Func,
+    types::{FuncSig, MemoryDescriptor, Type, Value},
+    units::Pages,
+    vm, Instance,
 };
 use wasmer_runtime_core_tests::{get_compiler, wat2wasm};
 
@@ -68,6 +75,7 @@ fn imported_functions_forms(test: &dyn Fn(&Instance)) {
   (import "env" "memory" (memory 1 1))
   (import "env" "callback_fn" (func $callback_fn (type $type)))
   (import "env" "callback_closure" (func $callback_closure (type $type)))
+  (import "env" "callback_closure_polymorphic" (func $callback_closure_polymorphic (type $type)))
   (import "env" "callback_closure_with_env" (func $callback_closure_with_env (type $type)))
   (import "env" "callback_fn_with_vmctx" (func $callback_fn_with_vmctx (type $type)))
   (import "env" "callback_closure_with_vmctx" (func $callback_closure_with_vmctx (type $type)))
@@ -86,6 +94,10 @@ fn imported_functions_forms(test: &dyn Fn(&Instance)) {
     get_local 0
     call $callback_closure)
 
+  (func (export "function_closure_polymorphic") (type $type)
+    get_local 0
+    call $callback_closure_polymorphic)
+
   (func (export "function_closure_with_env") (type $type)
     get_local 0
     call $callback_closure_with_env)
@@ -142,6 +154,16 @@ fn imported_functions_forms(test: &dyn Fn(&Instance)) {
                 Ok(n + 1)
             }),
 
+            "callback_closure_polymorphic" => Func::<i32, i32, _>::new_polymorphic(
+                Arc::new(FuncSig::new(vec![Type::I32], vec![Type::I32])),
+                |_, params| -> Vec<Value> {
+                    match params[0] {
+                        Value::I32(x) => vec![Value::I32(x + 1)],
+                        _ => unreachable!()
+                    }
+                }
+            ),
+
             // Closure with a captured environment (a single variable + an instance of `Memory`).
             "callback_closure_with_env" => Func::new(move |n: i32| -> Result<i32, ()> {
                 let shift_ = shift + memory.view::<i32>()[0].get();
@@ -236,6 +258,11 @@ macro_rules! test {
 
 test!(test_fn, function_fn, Ok(2));
 test!(test_closure, function_closure, Ok(2));
+test!(
+    test_closure_polymorphic,
+    function_closure_polymorphic,
+    Ok(2)
+);
 test!(
     test_closure_with_env,
     function_closure_with_env,

lib/runtime-core/src/loader.rs

@@ -1,7 +1,9 @@
 //! The loader module functions are used to load an instance.
 use crate::{backend::RunnableModule, module::ModuleInfo, types::Type, types::Value, vm::Ctx};
 #[cfg(unix)]
-use libc::{mmap, mprotect, munmap, MAP_ANON, MAP_PRIVATE, PROT_EXEC, PROT_READ, PROT_WRITE};
+use libc::{
+    mmap, mprotect, munmap, MAP_ANON, MAP_NORESERVE, MAP_PRIVATE, PROT_EXEC, PROT_READ, PROT_WRITE,
+};
 use std::{
     fmt::Debug,
     ops::{Deref, DerefMut},
@@ -169,7 +171,7 @@ impl CodeMemory {
                 std::ptr::null_mut(),
                 size,
                 PROT_READ | PROT_WRITE,
-                MAP_PRIVATE | MAP_ANON,
+                MAP_PRIVATE | MAP_ANON | MAP_NORESERVE,
                 -1,
                 0,
             )
@@ -196,6 +198,20 @@ impl CodeMemory {
             panic!("cannot set code memory to writable");
         }
     }
+
+    /// Makes this code memory both writable and executable.
+    ///
+    /// Avoid using this if a combination `make_executable` and `make_writable` can be used.
+    pub fn make_writable_executable(&self) {
+        if unsafe { mprotect(self.ptr as _, self.size, PROT_READ | PROT_WRITE | PROT_EXEC) } != 0 {
+            panic!("cannot set code memory to writable and executable");
+        }
+    }
+
+    /// Returns the backing pointer of this code memory.
+    pub fn get_backing_ptr(&self) -> *mut u8 {
+        self.ptr
+    }
 }
 
 #[cfg(unix)]

lib/runtime-core/src/trampoline_x64.rs

@@ -9,6 +9,8 @@
 use crate::loader::CodeMemory;
 use crate::vm::Ctx;
 use std::fmt;
+use std::ptr::NonNull;
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::{mem, slice};
 
 lazy_static! {
@@ -29,6 +31,50 @@ lazy_static! {
             mem::transmute(ptr)
         }
     };
+
+    static ref TRAMPOLINES: TrampBuffer = TrampBuffer::new();
+}
+
+struct TrampBuffer {
+    buffer: CodeMemory,
+    len: AtomicUsize,
+}
+
+impl TrampBuffer {
+    /// Creates a trampoline buffer.
+    fn new() -> TrampBuffer {
+        // Pre-allocate 64 MiB of virtual memory for code.
+        let mem = CodeMemory::new(64 * 1048576);
+        mem.make_writable_executable();
+        TrampBuffer {
+            buffer: mem,
+            len: AtomicUsize::new(0),
+        }
+    }
+
+    /// Bump allocation. Copies `buf` to the end of this code memory.
+    ///
+    /// FIXME: Proper storage recycling.
+    fn append(&self, buf: &[u8]) -> Option<NonNull<u8>> {
+        let begin = self.len.fetch_add(buf.len(), Ordering::SeqCst);
+        let end = begin + buf.len();
+
+        // Length overflowed. Revert and return None.
+        if end > self.buffer.len() {
+            self.len.fetch_sub(buf.len(), Ordering::SeqCst);
+            return None;
+        }
+
+        // Now we have unique ownership to `self.buffer[begin..end]`.
+        let slice = unsafe {
+            std::slice::from_raw_parts_mut(
+                self.buffer.get_backing_ptr().offset(begin as _),
+                buf.len(),
+            )
+        };
+        slice.copy_from_slice(buf);
+        Some(NonNull::new(slice.as_mut_ptr()).unwrap())
+    }
 }
 
 /// An opaque type for pointers to a callable memory location.
@@ -219,6 +265,11 @@ impl TrampolineBufferBuilder {
         idx
     }
 
+    /// Appends to the global trampoline buffer.
+    pub fn append_global(self) -> Option<NonNull<u8>> {
+        TRAMPOLINES.append(&self.code)
+    }
+
     /// Consumes the builder and builds the trampoline buffer.
     pub fn build(self) -> TrampolineBuffer {
         get_context(); // ensure lazy initialization is completed

lib/runtime-core/src/typed_func.rs

@@ -240,6 +240,79 @@ where
             _phantom: PhantomData,
         }
     }
+
+    /// Creates a polymorphic function.
+    #[allow(unused_variables)]
+    #[cfg(all(unix, target_arch = "x86_64"))]
+    pub fn new_polymorphic<F>(signature: Arc<FuncSig>, func: F) -> Func<'a, Args, Rets, Host>
+    where
+        F: Fn(&mut vm::Ctx, &[crate::types::Value]) -> Vec<crate::types::Value> + 'static,
+    {
+        use crate::trampoline_x64::*;
+        use crate::types::Value;
+        use std::convert::TryFrom;
+
+        struct PolymorphicContext {
+            arg_types: Vec<Type>,
+            func: Box<Fn(&mut vm::Ctx, &[Value]) -> Vec<Value>>,
+        }
+        unsafe extern "C" fn enter_host_polymorphic(
+            ctx: *const CallContext,
+            args: *const u64,
+        ) -> u64 {
+            let ctx = &*(ctx as *const PolymorphicContext);
+            let vmctx = &mut *(*args.offset(0) as *mut vm::Ctx);
+            let args: Vec<Value> = ctx
+                .arg_types
+                .iter()
+                .enumerate()
+                .map(|(i, t)| {
+                    let i = i + 1; // skip vmctx
+                    match *t {
+                        Type::I32 => Value::I32(*args.offset(i as _) as i32),
+                        Type::I64 => Value::I64(*args.offset(i as _) as i64),
+                        Type::F32 => Value::F32(f32::from_bits(*args.offset(i as _) as u32)),
+                        Type::F64 => Value::F64(f64::from_bits(*args.offset(i as _) as u64)),
+                        Type::V128 => {
+                            panic!("enter_host_polymorphic: 128-bit types are not supported")
+                        }
+                    }
+                })
+                .collect();
+            let rets = (ctx.func)(vmctx, &args);
+            if rets.len() == 0 {
+                0
+            } else if rets.len() == 1 {
+                u64::try_from(rets[0].to_u128()).expect(
+                    "128-bit return value from polymorphic host functions is not yet supported",
+                )
+            } else {
+                panic!(
+                    "multiple return values from polymorphic host functions is not yet supported"
+                );
+            }
+        }
+        let mut builder = TrampolineBufferBuilder::new();
+        let ctx = Box::new(PolymorphicContext {
+            arg_types: signature.params().to_vec(),
+            func: Box::new(func),
+        });
+        builder.add_callinfo_trampoline(
+            enter_host_polymorphic,
+            Box::into_raw(ctx) as *const _,
+            (signature.params().len() + 1) as u32, // +vmctx
+        );
+        let ptr = builder
+            .append_global()
+            .expect("cannot bump-allocate global trampoline memory");
+        Func {
+            inner: Host(()),
+            func: ptr.cast::<vm::Func>(),
+            func_env: None,
+            vmctx: ptr::null_mut(),
+            _phantom: PhantomData,
+        }
+    }
 }
 
 impl<'a, Args, Rets, Inner> Func<'a, Args, Rets, Inner>

lib/runtime-core/src/vm.rs

@@ -545,13 +545,13 @@ impl Ctx {
 /// `typed_func` module within the `wrap` functions, to wrap imported
 /// functions.
 #[repr(transparent)]
-pub struct Func(pub(self) *mut c_void);
+pub struct Func(*mut c_void);
 
 /// Represents a function environment pointer, like a captured
 /// environment of a closure. It is mostly used in the `typed_func`
 /// module within the `wrap` functions, to wrap imported functions.
 #[repr(transparent)]
-pub struct FuncEnv(pub(self) *mut c_void);
+pub struct FuncEnv(*mut c_void);
 
 /// Represents a function context. It is used by imported functions
 /// only.