wasmtime_environ/compile/
mod.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
//! A `Compilation` contains the compiled function bodies for a WebAssembly
//! module.

use crate::prelude::*;
use crate::{obj, Tunables};
use crate::{
    BuiltinFunctionIndex, DefinedFuncIndex, FlagValue, FuncIndex, FunctionLoc, ObjectKind,
    PrimaryMap, StaticModuleIndex, WasmError, WasmFuncType, WasmFunctionInfo,
};
use anyhow::Result;
use object::write::{Object, SymbolId};
use object::{Architecture, BinaryFormat, FileFlags};
use std::any::Any;
use std::borrow::Cow;
use std::fmt;
use std::path;
use std::sync::Arc;

mod address_map;
mod module_artifacts;
mod module_environ;
mod module_types;
mod trap_encoding;

pub use self::address_map::*;
pub use self::module_artifacts::*;
pub use self::module_environ::*;
pub use self::module_types::*;
pub use self::trap_encoding::*;

/// An error while compiling WebAssembly to machine code.
#[derive(Debug)]
pub enum CompileError {
    /// A wasm translation error occurred.
    Wasm(WasmError),

    /// A compilation error occurred.
    Codegen(String),

    /// A compilation error occurred.
    DebugInfoNotSupported,
}

impl fmt::Display for CompileError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            CompileError::Wasm(_) => write!(f, "WebAssembly translation error"),
            CompileError::Codegen(s) => write!(f, "Compilation error: {s}"),
            CompileError::DebugInfoNotSupported => {
                write!(f, "Debug info is not supported with this configuration")
            }
        }
    }
}

impl From<WasmError> for CompileError {
    fn from(err: WasmError) -> CompileError {
        CompileError::Wasm(err)
    }
}

#[cfg(feature = "std")]
impl std::error::Error for CompileError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            CompileError::Wasm(e) => Some(e),
            _ => None,
        }
    }
}

/// What relocations can be applied against.
///
/// Each wasm function may refer to various other `RelocationTarget` entries.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum RelocationTarget {
    /// This is a reference to another defined wasm function in the same module.
    Wasm(FuncIndex),
    /// This is a reference to a trampoline for a builtin function.
    Builtin(BuiltinFunctionIndex),
    /// A compiler-generated libcall.
    HostLibcall(obj::LibCall),
}

/// Implementation of an incremental compilation's key/value cache store.
///
/// In theory, this could just be Cranelift's `CacheKvStore` trait, but it is not as we want to
/// make sure that wasmtime isn't too tied to Cranelift internals (and as a matter of fact, we
/// can't depend on the Cranelift trait here).
pub trait CacheStore: Send + Sync + std::fmt::Debug {
    /// Try to retrieve an arbitrary cache key entry, and returns a reference to bytes that were
    /// inserted via `Self::insert` before.
    fn get(&self, key: &[u8]) -> Option<Cow<[u8]>>;

    /// Given an arbitrary key and bytes, stores them in the cache.
    ///
    /// Returns false when insertion in the cache failed.
    fn insert(&self, key: &[u8], value: Vec<u8>) -> bool;
}

/// Abstract trait representing the ability to create a `Compiler` below.
///
/// This is used in Wasmtime to separate compiler implementations, currently
/// mostly used to separate Cranelift from Wasmtime itself.
pub trait CompilerBuilder: Send + Sync + fmt::Debug {
    /// Sets the target of compilation to the target specified.
    fn target(&mut self, target: target_lexicon::Triple) -> Result<()>;

    /// Enables clif output in the directory specified.
    fn clif_dir(&mut self, _path: &path::Path) -> Result<()> {
        anyhow::bail!("clif output not supported");
    }

    /// Returns the currently configured target triple that compilation will
    /// produce artifacts for.
    fn triple(&self) -> &target_lexicon::Triple;

    /// Compiler-specific method to configure various settings in the compiler
    /// itself.
    ///
    /// This is expected to be defined per-compiler. Compilers should return
    /// errors for unknown names/values.
    fn set(&mut self, name: &str, val: &str) -> Result<()>;

    /// Compiler-specific method for configuring settings.
    ///
    /// Same as [`CompilerBuilder::set`] except for enabling boolean flags.
    /// Currently cranelift uses this to sometimes enable a family of settings.
    fn enable(&mut self, name: &str) -> Result<()>;

    /// Returns a list of all possible settings that can be configured with
    /// [`CompilerBuilder::set`] and [`CompilerBuilder::enable`].
    fn settings(&self) -> Vec<Setting>;

    /// Enables Cranelift's incremental compilation cache, using the given `CacheStore`
    /// implementation.
    ///
    /// This will return an error if the compiler does not support incremental compilation.
    fn enable_incremental_compilation(&mut self, cache_store: Arc<dyn CacheStore>) -> Result<()>;

    /// Set the tunables for this compiler.
    fn set_tunables(&mut self, tunables: Tunables) -> Result<()>;

    /// Builds a new [`Compiler`] object from this configuration.
    fn build(&self) -> Result<Box<dyn Compiler>>;

    /// Enables or disables wmemcheck during runtime according to the wmemcheck CLI flag.
    fn wmemcheck(&mut self, _enable: bool) {}
}

/// Description of compiler settings returned by [`CompilerBuilder::settings`].
#[derive(Clone, Copy, Debug)]
pub struct Setting {
    /// The name of the setting.
    pub name: &'static str,
    /// The description of the setting.
    pub description: &'static str,
    /// The kind of the setting.
    pub kind: SettingKind,
    /// The supported values of the setting (for enum values).
    pub values: Option<&'static [&'static str]>,
}

/// Different kinds of [`Setting`] values that can be configured in a
/// [`CompilerBuilder`]
#[derive(Clone, Copy, Debug)]
pub enum SettingKind {
    /// The setting is an enumeration, meaning it's one of a set of values.
    Enum,
    /// The setting is a number.
    Num,
    /// The setting is a boolean.
    Bool,
    /// The setting is a preset.
    Preset,
}

/// An implementation of a compiler which can compile WebAssembly functions to
/// machine code and perform other miscellaneous tasks needed by the JIT runtime.
pub trait Compiler: Send + Sync {
    /// Compiles the function `index` within `translation`.
    ///
    /// The body of the function is available in `data` and configuration
    /// values are also passed in via `tunables`. Type information in
    /// `translation` is all relative to `types`.
    ///
    /// This function returns a tuple:
    ///
    /// 1. Metadata about the wasm function itself.
    /// 2. The function itself, as an `Any` to get downcasted later when passed
    ///    to `append_code`.
    fn compile_function(
        &self,
        translation: &ModuleTranslation<'_>,
        index: DefinedFuncIndex,
        data: FunctionBodyData<'_>,
        types: &ModuleTypesBuilder,
    ) -> Result<(WasmFunctionInfo, Box<dyn Any + Send>), CompileError>;

    /// Compile a trampoline for an array-call host function caller calling the
    /// `index`th Wasm function.
    ///
    /// The trampoline should save the necessary state to record the
    /// host-to-Wasm transition (e.g. registers used for fast stack walking).
    fn compile_array_to_wasm_trampoline(
        &self,
        translation: &ModuleTranslation<'_>,
        types: &ModuleTypesBuilder,
        index: DefinedFuncIndex,
    ) -> Result<Box<dyn Any + Send>, CompileError>;

    /// Compile a trampoline for a Wasm caller calling a array callee with the
    /// given signature.
    ///
    /// The trampoline should save the necessary state to record the
    /// Wasm-to-host transition (e.g. registers used for fast stack walking).
    fn compile_wasm_to_array_trampoline(
        &self,
        wasm_func_ty: &WasmFuncType,
    ) -> Result<Box<dyn Any + Send>, CompileError>;

    /// Creates a tramopline that can be used to call Wasmtime's implementation
    /// of the builtin function specified by `index`.
    ///
    /// The trampoline created can technically have any ABI but currently has
    /// the native ABI. This will then perform all the necessary duties of an
    /// exit trampoline from wasm and then perform the actual dispatch to the
    /// builtin function. Builtin functions in Wasmtime are stored in an array
    /// in all `VMContext` pointers, so the call to the host is an indirect
    /// call.
    fn compile_wasm_to_builtin(
        &self,
        index: BuiltinFunctionIndex,
    ) -> Result<Box<dyn Any + Send>, CompileError>;

    /// Returns the list of relocations required for a function from one of the
    /// previous `compile_*` functions above.
    fn compiled_function_relocation_targets<'a>(
        &'a self,
        func: &'a dyn Any,
    ) -> Box<dyn Iterator<Item = RelocationTarget> + 'a>;

    /// Appends a list of compiled functions to an in-memory object.
    ///
    /// This function will receive the same `Box<dyn Any>` produced as part of
    /// compilation from functions like `compile_function`,
    /// `compile_host_to_wasm_trampoline`, and other component-related shims.
    /// Internally this will take all of these functions and add information to
    /// the object such as:
    ///
    /// * Compiled code in a `.text` section
    /// * Unwind information in Wasmtime-specific sections
    /// * Relocations, if necessary, for the text section
    ///
    /// Each function is accompanied with its desired symbol name and the return
    /// value of this function is the symbol for each function as well as where
    /// each function was placed within the object.
    ///
    /// The `resolve_reloc` argument is intended to resolving relocations
    /// between function, chiefly resolving intra-module calls within one core
    /// wasm module. The closure here takes two arguments:
    ///
    /// 1. First, the index within `funcs` that is being resolved,
    ///
    /// 2. and next the `RelocationTarget` which is the relocation target to
    ///    resolve.
    ///
    /// The return value is an index within `funcs` that the relocation points
    /// to.
    fn append_code(
        &self,
        obj: &mut Object<'static>,
        funcs: &[(String, Box<dyn Any + Send>)],
        resolve_reloc: &dyn Fn(usize, RelocationTarget) -> usize,
    ) -> Result<Vec<(SymbolId, FunctionLoc)>>;

    /// Creates a new `Object` file which is used to build the results of a
    /// compilation into.
    ///
    /// The returned object file will have an appropriate
    /// architecture/endianness for `self.triple()`, but at this time it is
    /// always an ELF file, regardless of target platform.
    fn object(&self, kind: ObjectKind) -> Result<Object<'static>> {
        use target_lexicon::Architecture::*;

        let triple = self.triple();
        let mut obj = Object::new(
            BinaryFormat::Elf,
            match triple.architecture {
                X86_32(_) => Architecture::I386,
                X86_64 => Architecture::X86_64,
                Arm(_) => Architecture::Arm,
                Aarch64(_) => Architecture::Aarch64,
                S390x => Architecture::S390x,
                Riscv64(_) => Architecture::Riscv64,
                // XXX: the `object` crate won't successfully build an object
                // with relocations and such if it doesn't know the
                // architecture, so just pretend we are riscv64. Yolo!
                Pulley32 | Pulley64 => Architecture::Riscv64,
                architecture => {
                    anyhow::bail!("target architecture {:?} is unsupported", architecture,);
                }
            },
            match triple.endianness().unwrap() {
                target_lexicon::Endianness::Little => object::Endianness::Little,
                target_lexicon::Endianness::Big => object::Endianness::Big,
            },
        );
        obj.flags = FileFlags::Elf {
            os_abi: obj::ELFOSABI_WASMTIME,
            e_flags: match kind {
                ObjectKind::Module => obj::EF_WASMTIME_MODULE,
                ObjectKind::Component => obj::EF_WASMTIME_COMPONENT,
            },
            abi_version: 0,
        };
        Ok(obj)
    }

    /// Returns the target triple that this compiler is compiling for.
    fn triple(&self) -> &target_lexicon::Triple;

    /// Returns the alignment necessary to align values to the page size of the
    /// compilation target. Note that this may be an upper-bound where the
    /// alignment is larger than necessary for some platforms since it may
    /// depend on the platform's runtime configuration.
    fn page_size_align(&self) -> u64 {
        use target_lexicon::*;
        match (self.triple().operating_system, self.triple().architecture) {
            (
                OperatingSystem::MacOSX { .. }
                | OperatingSystem::Darwin
                | OperatingSystem::Ios
                | OperatingSystem::Tvos,
                Architecture::Aarch64(..),
            ) => 0x4000,
            // 64 KB is the maximal page size (i.e. memory translation granule size)
            // supported by the architecture and is used on some platforms.
            (_, Architecture::Aarch64(..)) => 0x10000,
            _ => 0x1000,
        }
    }

    /// Returns a list of configured settings for this compiler.
    fn flags(&self) -> Vec<(&'static str, FlagValue<'static>)>;

    /// Same as [`Compiler::flags`], but ISA-specific (a cranelift-ism)
    fn isa_flags(&self) -> Vec<(&'static str, FlagValue<'static>)>;

    /// Get a flag indicating whether branch protection is enabled.
    fn is_branch_protection_enabled(&self) -> bool;

    /// Returns a suitable compiler usable for component-related compilations.
    ///
    /// Note that the `ComponentCompiler` trait can also be implemented for
    /// `Self` in which case this function would simply return `self`.
    #[cfg(feature = "component-model")]
    fn component_compiler(&self) -> &dyn crate::component::ComponentCompiler;

    /// Appends generated DWARF sections to the `obj` specified.
    ///
    /// The `translations` track all compiled functions and `get_func` can be
    /// used to acquire the metadata for a particular function within a module.
    fn append_dwarf<'a>(
        &self,
        obj: &mut Object<'_>,
        translations: &'a PrimaryMap<StaticModuleIndex, ModuleTranslation<'a>>,
        get_func: &'a dyn Fn(
            StaticModuleIndex,
            DefinedFuncIndex,
        ) -> (SymbolId, &'a (dyn Any + Send)),
        dwarf_package_bytes: Option<&'a [u8]>,
        tunables: &'a Tunables,
    ) -> Result<()>;

    /// Creates a new System V Common Information Entry for the ISA.
    ///
    /// Returns `None` if the ISA does not support System V unwind information.
    fn create_systemv_cie(&self) -> Option<gimli::write::CommonInformationEntry> {
        // By default, an ISA cannot create a System V CIE.
        None
    }
}