Better Wasmtime API for embedder (#287)

* Migrate wasm-rust-api code to wasmtime.

wasmtime-api/src/trampoline/code_memory.rs

@@ -0,0 +1,83 @@
+//! Memory management for executable code.
+// Copy of wasmtime's wasmtime-jit/src/code_memory.rs
+
+use core::{cmp, mem};
+use region;
+use std::string::String;
+use std::vec::Vec;
+use wasmtime_runtime::{Mmap, VMFunctionBody};
+
+/// Memory manager for executable code.
+pub(crate) struct CodeMemory {
+    current: Mmap,
+    mmaps: Vec<Mmap>,
+    position: usize,
+    published: usize,
+}
+
+impl CodeMemory {
+    /// Create a new `CodeMemory` instance.
+    pub fn new() -> Self {
+        Self {
+            current: Mmap::new(),
+            mmaps: Vec::new(),
+            position: 0,
+            published: 0,
+        }
+    }
+
+    /// Allocate `size` bytes of memory which can be made executable later by
+    /// calling `publish()`. Note that we allocate the memory as writeable so
+    /// that it can be written to and patched, though we make it readonly before
+    /// actually executing from it.
+    ///
+    /// TODO: Add an alignment flag.
+    fn allocate(&mut self, size: usize) -> Result<&mut [u8], String> {
+        if self.current.len() - self.position < size {
+            self.mmaps.push(mem::replace(
+                &mut self.current,
+                Mmap::with_at_least(cmp::max(0x10000, size))?,
+            ));
+            self.position = 0;
+        }
+        let old_position = self.position;
+        self.position += size;
+        Ok(&mut self.current.as_mut_slice()[old_position..self.position])
+    }
+
+    /// Convert mut a slice from u8 to VMFunctionBody.
+    fn view_as_mut_vmfunc_slice(slice: &mut [u8]) -> &mut [VMFunctionBody] {
+        let byte_ptr: *mut [u8] = slice;
+        let body_ptr = byte_ptr as *mut [VMFunctionBody];
+        unsafe { &mut *body_ptr }
+    }
+
+    /// Allocate enough memory to hold a copy of `slice` and copy the data into it.
+    /// TODO: Reorganize the code that calls this to emit code directly into the
+    /// mmap region rather than into a Vec that we need to copy in.
+    pub fn allocate_copy_of_byte_slice(
+        &mut self,
+        slice: &[u8],
+    ) -> Result<&mut [VMFunctionBody], String> {
+        let new = self.allocate(slice.len())?;
+        new.copy_from_slice(slice);
+        Ok(Self::view_as_mut_vmfunc_slice(new))
+    }
+
+    /// Make all allocated memory executable.
+    pub fn publish(&mut self) {
+        self.mmaps
+            .push(mem::replace(&mut self.current, Mmap::new()));
+        self.position = 0;
+
+        for m in &mut self.mmaps[self.published..] {
+            if m.len() != 0 {
+                unsafe {
+                    region::protect(m.as_mut_ptr(), m.len(), region::Protection::ReadExecute)
+                }
+                .expect("unable to make memory readonly and executable");
+            }
+        }
+        self.published = self.mmaps.len();
+    }
+}

wasmtime-api/src/trampoline/create_handle.rs

@@ -0,0 +1,289 @@
+//! Support for a calling of an imported function.
+
+use crate::trampoline::code_memory::CodeMemory;
+use cranelift_codegen::ir::types;
+use cranelift_codegen::ir::{InstBuilder, StackSlotData, StackSlotKind, TrapCode};
+use cranelift_codegen::Context;
+use cranelift_codegen::{binemit, ir, isa};
+use cranelift_entity::{EntityRef, PrimaryMap};
+use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
+use cranelift_wasm::{DefinedFuncIndex, FuncIndex};
+//use target_lexicon::HOST;
+use failure::Error;
+use wasmtime_environ::{Export, Module};
+use wasmtime_runtime::{Imports, InstanceHandle, VMContext, VMFunctionBody};
+
+use core::cmp;
+use std::cell::RefCell;
+use std::collections::{HashMap, HashSet};
+use std::rc::Rc;
+
+use crate::{Func, Trap, Val};
+
+struct TrampolineState {
+    func: Rc<RefCell<Func>>,
+    trap: Option<Rc<RefCell<Trap>>>,
+    #[allow(dead_code)]
+    code_memory: CodeMemory,
+}
+
+unsafe extern "C" fn stub_fn(vmctx: *mut VMContext, call_id: u32, values_vec: *mut i64) -> u32 {
+    let mut instance = InstanceHandle::from_vmctx(vmctx);
+
+    let (args, returns_len) = {
+        let module = instance.module_ref();
+        let signature = &module.signatures[module.functions[FuncIndex::new(call_id as usize)]];
+
+        let mut args = Vec::new();
+        for i in 1..signature.params.len() {
+            args.push(Val::read_value_from(
+                values_vec.offset(i as isize - 1),
+                signature.params[i].value_type,
+            ))
+        }
+        (args, signature.returns.len())
+    };
+
+    let func = instance
+        .host_state()
+        .downcast_mut::<TrampolineState>()
+        .expect("state")
+        .func
+        .borrow();
+
+    match func.call(&args) {
+        Ok(returns) => {
+            for i in 0..returns_len {
+                // TODO check signature.returns[i].value_type ?
+                returns[i].write_value_to(values_vec.offset(i as isize));
+            }
+            0
+        }
+        Err(trap) => {
+            // TODO read custom exception
+            InstanceHandle::from_vmctx(vmctx)
+                .host_state()
+                .downcast_mut::<TrampolineState>()
+                .expect("state")
+                .trap = Some(trap);
+            1
+        }
+    }
+}
+
+/// Create a trampoline for invoking a Callable.
+fn make_trampoline(
+    isa: &dyn isa::TargetIsa,
+    code_memory: &mut CodeMemory,
+    fn_builder_ctx: &mut FunctionBuilderContext,
+    call_id: u32,
+    signature: &ir::Signature,
+) -> *const VMFunctionBody {
+    // Mostly reverse copy of the similar method from wasmtime's
+    // wasmtime-jit/src/compiler.rs.
+    let pointer_type = isa.pointer_type();
+    let mut stub_sig = ir::Signature::new(isa.frontend_config().default_call_conv);
+
+    // Add the `vmctx` parameter.
+    stub_sig.params.push(ir::AbiParam::special(
+        pointer_type,
+        ir::ArgumentPurpose::VMContext,
+    ));
+
+    // Add the `call_id` parameter.
+    stub_sig.params.push(ir::AbiParam::new(types::I32));
+
+    // Add the `values_vec` parameter.
+    stub_sig.params.push(ir::AbiParam::new(pointer_type));
+
+    // Add error/trap return.
+    stub_sig.returns.push(ir::AbiParam::new(types::I32));
+
+    let values_vec_len = 8 * cmp::max(signature.params.len() - 1, signature.returns.len()) as u32;
+
+    let mut context = Context::new();
+    context.func =
+        ir::Function::with_name_signature(ir::ExternalName::user(0, 0), signature.clone());
+
+    let ss = context.func.create_stack_slot(StackSlotData::new(
+        StackSlotKind::ExplicitSlot,
+        values_vec_len,
+    ));
+    let value_size = 8;
+
+    {
+        let mut builder = FunctionBuilder::new(&mut context.func, fn_builder_ctx);
+        let block0 = builder.create_ebb();
+
+        builder.append_ebb_params_for_function_params(block0);
+        builder.switch_to_block(block0);
+        builder.seal_block(block0);
+
+        let values_vec_ptr_val = builder.ins().stack_addr(pointer_type, ss, 0);
+        let mflags = ir::MemFlags::trusted();
+        for i in 1..signature.params.len() {
+            if i == 0 {
+                continue;
+            }
+
+            let val = builder.func.dfg.ebb_params(block0)[i];
+            builder.ins().store(
+                mflags,
+                val,
+                values_vec_ptr_val,
+                ((i - 1) * value_size) as i32,
+            );
+        }
+
+        let vmctx_ptr_val = builder.func.dfg.ebb_params(block0)[0];
+        let call_id_val = builder.ins().iconst(types::I32, call_id as i64);
+
+        let callee_args = vec![vmctx_ptr_val, call_id_val, values_vec_ptr_val];
+
+        let new_sig = builder.import_signature(stub_sig.clone());
+
+        let callee_value = builder
+            .ins()
+            .iconst(pointer_type, stub_fn as *const VMFunctionBody as i64);
+        let call = builder
+            .ins()
+            .call_indirect(new_sig, callee_value, &callee_args);
+
+        let call_result = builder.func.dfg.inst_results(call)[0];
+        builder.ins().trapnz(call_result, TrapCode::User(0));
+
+        let mflags = ir::MemFlags::trusted();
+        let mut results = Vec::new();
+        for (i, r) in signature.returns.iter().enumerate() {
+            let load = builder.ins().load(
+                r.value_type,
+                mflags,
+                values_vec_ptr_val,
+                (i * value_size) as i32,
+            );
+            results.push(load);
+        }
+        builder.ins().return_(&results);
+        builder.finalize()
+    }
+
+    let mut code_buf: Vec<u8> = Vec::new();
+    let mut reloc_sink = RelocSink {};
+    let mut trap_sink = binemit::NullTrapSink {};
+    let mut stackmap_sink = binemit::NullStackmapSink {};
+    context
+        .compile_and_emit(
+            isa,
+            &mut code_buf,
+            &mut reloc_sink,
+            &mut trap_sink,
+            &mut stackmap_sink,
+        )
+        .expect("compile_and_emit");
+
+    code_memory
+        .allocate_copy_of_byte_slice(&code_buf)
+        .expect("allocate_copy_of_byte_slice")
+        .as_ptr()
+}
+
+pub fn create_handle(func: &Rc<RefCell<Func>>) -> Result<InstanceHandle, Error> {
+    let sig = func.borrow().r#type().get_cranelift_signature().clone();
+
+    let isa = {
+        let isa_builder =
+            cranelift_native::builder().expect("host machine is not a supported target");
+        let flag_builder = cranelift_codegen::settings::builder();
+        isa_builder.finish(cranelift_codegen::settings::Flags::new(flag_builder))
+    };
+
+    let global_exports: Rc<RefCell<HashMap<String, Option<wasmtime_runtime::Export>>>> =
+        Rc::new(RefCell::new(HashMap::new()));
+    let mut fn_builder_ctx = FunctionBuilderContext::new();
+    let mut module = Module::new();
+    let mut finished_functions: PrimaryMap<DefinedFuncIndex, *const VMFunctionBody> =
+        PrimaryMap::new();
+    let mut code_memory = CodeMemory::new();
+
+    //let pointer_type = types::Type::triple_pointer_type(&HOST);
+    //let call_conv = isa::CallConv::triple_default(&HOST);
+
+    let dependencies = HashSet::new();
+    let memories = PrimaryMap::new();
+
+    let sig_id = module.signatures.push(sig.clone());
+    let func_id = module.functions.push(sig_id);
+    module
+        .exports
+        .insert("trampoline".to_string(), Export::Function(func_id));
+    let trampoline = make_trampoline(
+        isa.as_ref(),
+        &mut code_memory,
+        &mut fn_builder_ctx,
+        func_id.index() as u32,
+        &sig,
+    );
+    code_memory.publish();
+
+    finished_functions.push(trampoline);
+
+    let imports = Imports::new(
+        dependencies,
+        PrimaryMap::new(),
+        PrimaryMap::new(),
+        memories,
+        PrimaryMap::new(),
+    );
+    let data_initializers = Vec::new();
+    let signatures = PrimaryMap::new();
+
+    let trampoline_state = TrampolineState {
+        func: func.clone(),
+        trap: None,
+        code_memory,
+    };
+
+    Ok(InstanceHandle::new(
+        Rc::new(module),
+        global_exports,
+        finished_functions.into_boxed_slice(),
+        imports,
+        &data_initializers,
+        signatures.into_boxed_slice(),
+        None,
+        Box::new(trampoline_state),
+    )
+    .expect("instance"))
+}
+
+/// We don't expect trampoline compilation to produce any relocations, so
+/// this `RelocSink` just asserts that it doesn't recieve any.
+struct RelocSink {}
+
+impl binemit::RelocSink for RelocSink {
+    fn reloc_ebb(
+        &mut self,
+        _offset: binemit::CodeOffset,
+        _reloc: binemit::Reloc,
+        _ebb_offset: binemit::CodeOffset,
+    ) {
+        panic!("trampoline compilation should not produce ebb relocs");
+    }
+    fn reloc_external(
+        &mut self,
+        _offset: binemit::CodeOffset,
+        _reloc: binemit::Reloc,
+        _name: &ir::ExternalName,
+        _addend: binemit::Addend,
+    ) {
+        panic!("trampoline compilation should not produce external symbol relocs");
+    }
+    fn reloc_jt(
+        &mut self,
+        _offset: binemit::CodeOffset,
+        _reloc: binemit::Reloc,
+        _jt: ir::JumpTable,
+    ) {
+        panic!("trampoline compilation should not produce jump table relocs");
+    }
+}

wasmtime-api/src/trampoline/mod.rs

@@ -0,0 +1,19 @@
+//! Utility module to create trampolines in/out WebAssembly module.
+
+mod code_memory;
+mod create_handle;
+
+use failure::Error;
+use std::cell::RefCell;
+use std::rc::Rc;
+
+use self::create_handle::create_handle;
+use super::externals::Func;
+
+pub fn generate_func_export(f: &Rc<RefCell<Func>>) -> Result<(), Error> {
+    let mut instance = create_handle(f)?;
+    let export = instance.lookup("trampoline").expect("trampoline export");
+
+    f.borrow_mut().anchor = Some((instance, export));
+    Ok(())
+}