wasmtime-jit 0.3.0

//! JIT compilation.

use super::HashMap;
use crate::code_memory::CodeMemory;
use crate::instantiate::SetupError;
use crate::target_tunables::target_tunables;
use cranelift_codegen::ir::InstBuilder;
use cranelift_codegen::isa::{TargetFrontendConfig, TargetIsa};
use cranelift_codegen::Context;
use cranelift_codegen::{binemit, ir};
use cranelift_entity::{EntityRef, PrimaryMap};
use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
use cranelift_wasm::{DefinedFuncIndex, DefinedMemoryIndex};
use std::boxed::Box;
use std::string::String;
use std::vec::Vec;
use wasmtime_debug::{emit_debugsections_image, DebugInfoData};
use wasmtime_environ::{
    Compilation, CompileError, Compiler as _C, FunctionBodyData, Module, ModuleVmctxInfo,
    Relocations, Tunables, VMOffsets,
};
use wasmtime_runtime::{InstantiationError, SignatureRegistry, VMFunctionBody};

/// A WebAssembly code JIT compiler.
///
/// A `Compiler` instance owns the executable memory that it allocates.
///
/// TODO: Evolve this to support streaming rather than requiring a `&[u8]`
/// containing a whole wasm module at once.
///
/// TODO: Consider using cranelift-module.
pub struct Compiler {
    isa: Box<dyn TargetIsa>,

    code_memory: CodeMemory,
    trampoline_park: HashMap<*const VMFunctionBody, *const VMFunctionBody>,
    signatures: SignatureRegistry,

    /// The `FunctionBuilderContext`, shared between trampline function compilations.
    fn_builder_ctx: FunctionBuilderContext,
}

impl Compiler {
    /// Construct a new `Compiler`.
    pub fn new(isa: Box<dyn TargetIsa>) -> Self {
        Self {
            isa,
            code_memory: CodeMemory::new(),
            trampoline_park: HashMap::new(),
            signatures: SignatureRegistry::new(),
            fn_builder_ctx: FunctionBuilderContext::new(),
        }
    }
}

#[cfg(feature = "lightbeam")]
type DefaultCompiler = wasmtime_environ::lightbeam::Lightbeam;
#[cfg(not(feature = "lightbeam"))]
type DefaultCompiler = wasmtime_environ::cranelift::Cranelift;

impl Compiler {
    /// Return the target's frontend configuration settings.
    pub fn frontend_config(&self) -> TargetFrontendConfig {
        self.isa.frontend_config()
    }

    /// Return the tunables in use by this engine.
    pub fn tunables(&self) -> Tunables {
        target_tunables(self.isa.triple())
    }

    /// Compile the given function bodies.
    pub(crate) fn compile<'data>(
        &mut self,
        module: &Module,
        function_body_inputs: PrimaryMap<DefinedFuncIndex, FunctionBodyData<'data>>,
        debug_data: Option<DebugInfoData>,
    ) -> Result<
        (
            PrimaryMap<DefinedFuncIndex, *mut [VMFunctionBody]>,
            PrimaryMap<DefinedFuncIndex, ir::JumpTableOffsets>,
            Relocations,
            Option<Vec<u8>>,
        ),
        SetupError,
    > {
        let (compilation, relocations, address_transform, value_ranges, stack_slots) =
            DefaultCompiler::compile_module(
                module,
                function_body_inputs,
                &*self.isa,
                debug_data.is_some(),
            )
            .map_err(SetupError::Compile)?;

        let allocated_functions =
            allocate_functions(&mut self.code_memory, &compilation).map_err(|message| {
                SetupError::Instantiate(InstantiationError::Resource(format!(
                    "failed to allocate memory for functions: {}",
                    message
                )))
            })?;

        let dbg = if let Some(debug_data) = debug_data {
            let target_config = self.isa.frontend_config();
            let triple = self.isa.triple().clone();
            let mut funcs = Vec::new();
            for (i, allocated) in allocated_functions.into_iter() {
                let ptr = (*allocated) as *const u8;
                let body_len = compilation.get(i).body.len();
                funcs.push((ptr, body_len));
            }
            let module_vmctx_info = {
                let ofs = VMOffsets::new(target_config.pointer_bytes(), &module);
                let memory_offset =
                    ofs.vmctx_vmmemory_definition_base(DefinedMemoryIndex::new(0)) as i64;
                ModuleVmctxInfo {
                    memory_offset,
                    stack_slots,
                }
            };
            let bytes = emit_debugsections_image(
                triple,
                &target_config,
                &debug_data,
                &module_vmctx_info,
                &address_transform,
                &value_ranges,
                &funcs,
            )
            .map_err(|e| SetupError::DebugInfo(e))?;
            Some(bytes)
        } else {
            None
        };

        let jt_offsets = compilation.get_jt_offsets();

        Ok((allocated_functions, jt_offsets, relocations, dbg))
    }

    /// Create a trampoline for invoking a function.
    pub(crate) fn get_trampoline(
        &mut self,
        callee_address: *const VMFunctionBody,
        signature: &ir::Signature,
        value_size: usize,
    ) -> Result<*const VMFunctionBody, SetupError> {
        use super::hash_map::Entry::{Occupied, Vacant};
        Ok(match self.trampoline_park.entry(callee_address) {
            Occupied(entry) => *entry.get(),
            Vacant(entry) => {
                let body = make_trampoline(
                    &*self.isa,
                    &mut self.code_memory,
                    &mut self.fn_builder_ctx,
                    callee_address,
                    signature,
                    value_size,
                )?;
                entry.insert(body);
                body
            }
        })
    }

    /// Create and publish a trampoline for invoking a function.
    pub fn get_published_trampoline(
        &mut self,
        callee_address: *const VMFunctionBody,
        signature: &ir::Signature,
        value_size: usize,
    ) -> Result<*const VMFunctionBody, SetupError> {
        let result = self.get_trampoline(callee_address, signature, value_size)?;
        self.publish_compiled_code();
        Ok(result)
    }

    /// Make memory containing compiled code executable.
    pub(crate) fn publish_compiled_code(&mut self) {
        self.code_memory.publish();
    }

    pub(crate) fn signatures(&mut self) -> &mut SignatureRegistry {
        &mut self.signatures
    }
}

/// Create a trampoline for invoking a function.
fn make_trampoline(
    isa: &dyn TargetIsa,
    code_memory: &mut CodeMemory,
    fn_builder_ctx: &mut FunctionBuilderContext,
    callee_address: *const VMFunctionBody,
    signature: &ir::Signature,
    value_size: usize,
) -> Result<*const VMFunctionBody, SetupError> {
    let pointer_type = isa.pointer_type();
    let mut wrapper_sig = ir::Signature::new(isa.frontend_config().default_call_conv);

    // Add the `vmctx` parameter.
    wrapper_sig.params.push(ir::AbiParam::special(
        pointer_type,
        ir::ArgumentPurpose::VMContext,
    ));
    // Add the `values_vec` parameter.
    wrapper_sig.params.push(ir::AbiParam::new(pointer_type));

    let mut context = Context::new();
    context.func = ir::Function::with_name_signature(ir::ExternalName::user(0, 0), wrapper_sig);

    {
        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 (vmctx_ptr_val, values_vec_ptr_val) = {
            let params = builder.func.dfg.ebb_params(block0);
            (params[0], params[1])
        };

        // Load the argument values out of `values_vec`.
        let mflags = ir::MemFlags::trusted();
        let callee_args = signature
            .params
            .iter()
            .enumerate()
            .map(|(i, r)| {
                match r.purpose {
                    // i - 1 because vmctx isn't passed through `values_vec`.
                    ir::ArgumentPurpose::Normal => builder.ins().load(
                        r.value_type,
                        mflags,
                        values_vec_ptr_val,
                        ((i - 1) * value_size) as i32,
                    ),
                    ir::ArgumentPurpose::VMContext => vmctx_ptr_val,
                    other => panic!("unsupported argument purpose {}", other),
                }
            })
            .collect::<Vec<_>>();

        let new_sig = builder.import_signature(signature.clone());

        // TODO: It's possible to make this a direct call. We just need Cranelift
        // to support functions declared with an immediate integer address.
        // ExternalName::Absolute(u64). Let's do it.
        let callee_value = builder.ins().iconst(pointer_type, callee_address as i64);
        let call = builder
            .ins()
            .call_indirect(new_sig, callee_value, &callee_args);

        let results = builder.func.dfg.inst_results(call).to_vec();

        // Store the return values into `values_vec`.
        let mflags = ir::MemFlags::trusted();
        for (i, r) in results.iter().enumerate() {
            builder
                .ins()
                .store(mflags, *r, values_vec_ptr_val, (i * value_size) as i32);
        }

        builder.ins().return_(&[]);
        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,
        )
        .map_err(|error| SetupError::Compile(CompileError::Codegen(error)))?;

    Ok(code_memory
        .allocate_copy_of_byte_slice(&code_buf)
        .map_err(|message| SetupError::Instantiate(InstantiationError::Resource(message)))?
        .as_ptr())
}

fn allocate_functions(
    code_memory: &mut CodeMemory,
    compilation: &Compilation,
) -> Result<PrimaryMap<DefinedFuncIndex, *mut [VMFunctionBody]>, String> {
    // Allocate code for all function in one continuous memory block.
    // First, collect all function bodies into vector to pass to the
    // allocate_copy_of_byte_slices.
    let bodies = compilation
        .into_iter()
        .map(|code_and_jt| &code_and_jt.body[..])
        .collect::<Vec<&[u8]>>();
    let fat_ptrs = code_memory.allocate_copy_of_byte_slices(&bodies)?;
    // Second, create a PrimaryMap from result vector of pointers.
    let mut result = PrimaryMap::with_capacity(compilation.len());
    for i in 0..fat_ptrs.len() {
        let fat_ptr: *mut [VMFunctionBody] = fat_ptrs[i];
        result.push(fat_ptr);
    }
    Ok(result)
}

/// 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");
    }
}