wasmer_compiler_cranelift/translator/
func_translator.rs

1// This file contains code from external sources.
2// Attributions: https://github.com/wasmerio/wasmer/blob/main/docs/ATTRIBUTIONS.md
3
4//! Standalone WebAssembly to Cranelift IR translator.
5//!
6//! This module defines the `FuncTranslator` type which can translate a single WebAssembly
7//! function to Cranelift IR guided by a `FuncEnvironment` which provides information about the
8//! WebAssembly module and the runtime environment.
9
10use super::code_translator::translate_operator;
11use super::func_environ::{FuncEnvironment, ReturnMode};
12use super::func_state::FuncTranslationState;
13use super::translation_utils::get_vmctx_value_label;
14use crate::translator::EXN_REF_TYPE;
15use crate::translator::code_translator::bitcast_wasm_returns;
16use core::convert::TryFrom;
17use cranelift_codegen::entity::EntityRef;
18use cranelift_codegen::ir::{self, Block, InstBuilder, ValueLabel};
19use cranelift_codegen::timing;
20use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
21use wasmer_compiler::wasmparser::RefType;
22use wasmer_compiler::{FunctionBinaryReader, ModuleTranslationState, wptype_to_type};
23use wasmer_compiler::{wasm_unsupported, wasmparser};
24use wasmer_types::{LocalFunctionIndex, WasmResult};
25
26/// WebAssembly to Cranelift IR function translator.
27///
28/// A `FuncTranslator` is used to translate a binary WebAssembly function into Cranelift IR guided
29/// by a `FuncEnvironment` object. A single translator instance can be reused to translate multiple
30/// functions which will reduce heap allocation traffic.
31pub struct FuncTranslator {
32    func_ctx: FunctionBuilderContext,
33    state: FuncTranslationState,
34}
35
36impl wasmer_compiler::FuncTranslator for FuncTranslator {}
37
38impl FuncTranslator {
39    /// Create a new translator.
40    pub fn new() -> Self {
41        Self {
42            func_ctx: FunctionBuilderContext::new(),
43            state: FuncTranslationState::new(),
44        }
45    }
46
47    /// Translate a binary WebAssembly function.
48    ///
49    /// The `code` slice contains the binary WebAssembly *function code* as it appears in the code
50    /// section of a WebAssembly module, not including the initial size of the function code. The
51    /// slice is expected to contain two parts:
52    ///
53    /// - The declaration of *locals*, and
54    /// - The function *body* as an expression.
55    ///
56    /// See [the WebAssembly specification][wasm].
57    ///
58    /// [wasm]: https://webassembly.github.io/spec/core/binary/modules.html#code-section
59    ///
60    /// The Cranelift IR function `func` should be completely empty except for the `func.signature`
61    /// and `func.name` fields. The signature may contain special-purpose arguments which are not
62    /// regarded as WebAssembly local variables. Any signature arguments marked as
63    /// `ArgumentPurpose::Normal` are made accessible as WebAssembly local variables.
64    ///
65    pub fn translate<FE: FuncEnvironment + ?Sized>(
66        &mut self,
67        module_translation_state: &ModuleTranslationState,
68        reader: &mut dyn FunctionBinaryReader,
69        func: &mut ir::Function,
70        environ: &mut FE,
71        local_function_index: LocalFunctionIndex,
72    ) -> WasmResult<()> {
73        environ.push_params_on_stack(local_function_index);
74        self.translate_from_reader(module_translation_state, reader, func, environ)
75    }
76
77    /// Translate a binary WebAssembly function from a `FunctionBinaryReader`.
78    pub fn translate_from_reader<FE: FuncEnvironment + ?Sized>(
79        &mut self,
80        module_translation_state: &ModuleTranslationState,
81        reader: &mut dyn FunctionBinaryReader,
82        func: &mut ir::Function,
83        environ: &mut FE,
84    ) -> WasmResult<()> {
85        let _tt = timing::wasm_translate_function();
86        tracing::trace!(
87            "translate({} bytes, {}{})",
88            reader.bytes_remaining(),
89            func.name,
90            func.signature
91        );
92        debug_assert_eq!(func.dfg.num_blocks(), 0, "Function must be empty");
93        debug_assert_eq!(func.dfg.num_insts(), 0, "Function must be empty");
94
95        // This clears the `FunctionBuilderContext`.
96        let mut builder = FunctionBuilder::new(func, &mut self.func_ctx);
97        builder.set_srcloc(cur_srcloc(reader));
98        let entry_block = builder.create_block();
99        builder.append_block_params_for_function_params(entry_block);
100        builder.switch_to_block(entry_block); // This also creates values for the arguments.
101        builder.seal_block(entry_block); // Declare all predecessors known.
102
103        // Make sure the entry block is inserted in the layout before we make any callbacks to
104        // `environ`. The callback functions may need to insert things in the entry block.
105        builder.ensure_inserted_block();
106
107        let num_params = declare_wasm_parameters(&mut builder, entry_block, environ);
108
109        // Set up the translation state with a single pushed control block representing the whole
110        // function and its return values.
111        let exit_block = builder.create_block();
112        builder.append_block_params_for_function_returns(exit_block);
113        self.state.initialize(&builder.func.signature, exit_block);
114
115        parse_local_decls(reader, &mut builder, num_params, environ)?;
116        parse_function_body(
117            module_translation_state,
118            reader,
119            &mut builder,
120            &mut self.state,
121            environ,
122        )?;
123
124        builder.finalize();
125        Ok(())
126    }
127}
128
129/// Declare local variables for the signature parameters that correspond to WebAssembly locals.
130///
131/// Return the number of local variables declared.
132fn declare_wasm_parameters<FE: FuncEnvironment + ?Sized>(
133    builder: &mut FunctionBuilder,
134    entry_block: Block,
135    environ: &FE,
136) -> usize {
137    let sig_len = builder.func.signature.params.len();
138    let mut next_local = 0;
139    for i in 0..sig_len {
140        let param_type = builder.func.signature.params[i];
141        // There may be additional special-purpose parameters in addition to the normal WebAssembly
142        // signature parameters. For example, a `vmctx` pointer.
143        if environ.is_wasm_parameter(&builder.func.signature, i) {
144            // This is a normal WebAssembly signature parameter, so create a local for it.
145            let local = builder.declare_var(param_type.value_type);
146            let local_index = local.index();
147            debug_assert_eq!(local_index, next_local);
148            debug_assert!(u32::try_from(local_index).is_ok());
149            next_local += 1;
150
151            let param_value = builder.block_params(entry_block)[i];
152            builder.def_var(local, param_value);
153        }
154        if param_type.purpose == ir::ArgumentPurpose::VMContext {
155            let param_value = builder.block_params(entry_block)[i];
156            builder.set_val_label(param_value, get_vmctx_value_label());
157        }
158    }
159
160    next_local
161}
162
163/// Parse the local variable declarations that precede the function body.
164///
165/// Declare local variables, starting from `num_params`.
166fn parse_local_decls<FE: FuncEnvironment + ?Sized>(
167    reader: &mut dyn FunctionBinaryReader,
168    builder: &mut FunctionBuilder,
169    num_params: usize,
170    environ: &mut FE,
171) -> WasmResult<()> {
172    let mut next_local = num_params;
173    let local_count = reader.read_local_count()?;
174
175    for _ in 0..local_count {
176        builder.set_srcloc(cur_srcloc(reader));
177        let (count, ty) = reader.read_local_decl()?;
178        declare_locals(builder, count, ty, &mut next_local, environ)?;
179    }
180
181    Ok(())
182}
183
184/// Declare `count` local variables of the same type, starting from `next_local`.
185///
186/// Fail if the type is not valid for a local.
187fn declare_locals<FE: FuncEnvironment + ?Sized>(
188    builder: &mut FunctionBuilder,
189    count: u32,
190    wasm_type: wasmparser::ValType,
191    next_local: &mut usize,
192    environ: &mut FE,
193) -> WasmResult<()> {
194    // All locals are initialized to 0.
195    use wasmparser::ValType::*;
196    let zeroval = match wasm_type {
197        I32 => builder.ins().iconst(ir::types::I32, 0),
198        I64 => builder.ins().iconst(ir::types::I64, 0),
199        F32 => builder.ins().f32const(ir::immediates::Ieee32::with_bits(0)),
200        F64 => builder.ins().f64const(ir::immediates::Ieee64::with_bits(0)),
201        V128 => {
202            let constant_handle = builder.func.dfg.constants.insert([0; 16].to_vec().into());
203            builder.ins().vconst(ir::types::I8X16, constant_handle)
204        }
205        Ref(ty) => {
206            if ty.is_func_ref() || ty.is_extern_ref() {
207                builder.ins().iconst(environ.reference_type(), 0)
208            } else if ty == RefType::EXNREF || ty == RefType::EXN {
209                // no `.is_exnref` yet
210                builder.ins().iconst(EXN_REF_TYPE, 0)
211            } else {
212                return Err(wasm_unsupported!("unsupported reference type: {:?}", ty));
213            }
214        }
215    };
216
217    let wasmer_ty = wptype_to_type(wasm_type).unwrap();
218    let ty = builder.func.dfg.value_type(zeroval);
219    for _ in 0..count {
220        let local = builder.declare_var(ty);
221        let local_index = local.index();
222        debug_assert_eq!(local_index, *next_local);
223        debug_assert!(u32::try_from(local_index).is_ok());
224        builder.def_var(local, zeroval);
225        builder.set_val_label(zeroval, ValueLabel::new(*next_local));
226        environ.push_local_decl_on_stack(wasmer_ty);
227        *next_local += 1;
228    }
229    Ok(())
230}
231
232/// Parse the function body in `reader`.
233///
234/// This assumes that the local variable declarations have already been parsed and function
235/// arguments and locals are declared in the builder.
236fn parse_function_body<FE: FuncEnvironment + ?Sized>(
237    module_translation_state: &ModuleTranslationState,
238    reader: &mut dyn FunctionBinaryReader,
239    builder: &mut FunctionBuilder,
240    state: &mut FuncTranslationState,
241    environ: &mut FE,
242) -> WasmResult<()> {
243    // The control stack is initialized with a single block representing the whole function.
244    debug_assert_eq!(state.control_stack.len(), 1, "State not initialized");
245
246    // Keep going until the final `End` operator which pops the outermost block.
247    while !state.control_stack.is_empty() {
248        builder.set_srcloc(cur_srcloc(reader));
249        let op = reader.read_operator()?;
250        environ.before_translate_operator(&op, builder, state)?;
251        translate_operator(module_translation_state, &op, builder, state, environ)?;
252        environ.after_translate_operator(&op, builder, state)?;
253    }
254
255    // The final `End` operator left us in the exit block where we need to manually add a return
256    // instruction.
257    //
258    // If the exit block is unreachable, it may not have the correct arguments, so we would
259    // generate a return instruction that doesn't match the signature.
260    if state.reachable {
261        //debug_assert!(builder.is_pristine());
262        if !builder.is_unreachable() {
263            match environ.return_mode() {
264                ReturnMode::NormalReturns => {
265                    bitcast_wasm_returns(environ, &mut state.stack, builder);
266                    builder.ins().return_(&state.stack)
267                }
268            };
269        }
270    }
271
272    // Discard any remaining values on the stack. Either we just returned them,
273    // or the end of the function is unreachable.
274    state.stack.clear();
275    //state.metadata_stack.clear();
276
277    debug_assert!(reader.eof());
278
279    Ok(())
280}
281
282/// Get the current source location from a reader.
283fn cur_srcloc(reader: &dyn FunctionBinaryReader) -> ir::SourceLoc {
284    // We record source locations as byte code offsets relative to the beginning of the file.
285    // This will wrap around if byte code is larger than 4 GB.
286    ir::SourceLoc::new(reader.original_position() as u32)
287}
wasmer_compiler_cranelift/translator/func_translator.rs

wasmer_compiler_cranelift/translator/
func_translator.rs
