wasmtime_environ/compile/
module_artifacts.rs

1//! Definitions of runtime structures and metadata which are serialized into ELF
2//! with `postcard` as part of a module's compilation process.
3
4use crate::WasmChecksum;
5use crate::error::{Result, bail};
6use crate::prelude::*;
7use crate::{
8    CompiledModuleInfo, DebugInfoData, FunctionName, MemoryInitialization, Metadata,
9    ModuleTranslation, Tunables, obj,
10};
11use object::SectionKind;
12use object::write::{Object, SectionId, StandardSegment, WritableBuffer};
13use std::ops::Range;
14
15/// Helper structure to create an ELF file as a compilation artifact.
16///
17/// This structure exposes the process which Wasmtime will encode a core wasm
18/// module into an ELF file, notably managing data sections and all that good
19/// business going into the final file.
20pub struct ObjectBuilder<'a> {
21    /// The `object`-crate-defined ELF file write we're using.
22    obj: Object<'a>,
23
24    /// General compilation configuration.
25    tunables: &'a Tunables,
26
27    /// The section identifier for "rodata" which is where wasm data segments
28    /// will go.
29    data: SectionId,
30
31    /// The section identifier for function name information, or otherwise where
32    /// the `name` custom section of wasm is copied into.
33    ///
34    /// This is optional and lazily created on demand.
35    names: Option<SectionId>,
36
37    /// The section identifier for dwarf information copied from the original
38    /// wasm files.
39    ///
40    /// This is optional and lazily created on demand.
41    dwarf: Option<SectionId>,
42}
43
44impl<'a> ObjectBuilder<'a> {
45    /// Creates a new builder for the `obj` specified.
46    pub fn new(mut obj: Object<'a>, tunables: &'a Tunables) -> ObjectBuilder<'a> {
47        let data = obj.add_section(
48            obj.segment_name(StandardSegment::Data).to_vec(),
49            obj::ELF_WASM_DATA.as_bytes().to_vec(),
50            SectionKind::ReadOnlyData,
51        );
52        ObjectBuilder {
53            obj,
54            tunables,
55            data,
56            names: None,
57            dwarf: None,
58        }
59    }
60
61    /// Insert the wasm raw wasm-based debuginfo into the output.
62    /// Note that this is distinct from the native debuginfo
63    /// possibly generated by the native compiler, hence these sections
64    /// getting wasm-specific names.
65    pub fn push_debuginfo(
66        &mut self,
67        dwarf: &mut Vec<(u8, Range<u64>)>,
68        debuginfo: &DebugInfoData<'_>,
69    ) {
70        self.push_debug(dwarf, &debuginfo.dwarf.debug_abbrev);
71        self.push_debug(dwarf, &debuginfo.dwarf.debug_addr);
72        self.push_debug(dwarf, &debuginfo.dwarf.debug_aranges);
73        self.push_debug(dwarf, &debuginfo.dwarf.debug_info);
74        self.push_debug(dwarf, &debuginfo.dwarf.debug_line);
75        self.push_debug(dwarf, &debuginfo.dwarf.debug_line_str);
76        self.push_debug(dwarf, &debuginfo.dwarf.debug_str);
77        self.push_debug(dwarf, &debuginfo.dwarf.debug_str_offsets);
78        self.push_debug(dwarf, &debuginfo.debug_ranges);
79        self.push_debug(dwarf, &debuginfo.debug_rnglists);
80        self.push_debug(dwarf, &debuginfo.debug_cu_index);
81
82        // Sort this for binary-search-lookup later in `symbolize_context`.
83        dwarf.sort_by_key(|(id, _)| *id);
84    }
85
86    /// Completes compilation of the `translation` specified, inserting
87    /// everything necessary into the `Object` being built.
88    ///
89    /// This function will consume the final results of compiling a wasm module
90    /// and finish the ELF image in-progress as part of `self.obj` by appending
91    /// any compiler-agnostic sections.
92    ///
93    /// The auxiliary `CompiledModuleInfo` structure returned here has also been
94    /// serialized into the object returned, but if the caller will quickly
95    /// turn-around and invoke `CompiledModule::from_artifacts` after this then
96    /// the information can be passed to that method to avoid extra
97    /// deserialization. This is done to avoid a serialize-then-deserialize for
98    /// API calls like `Module::new` where the compiled module is immediately
99    /// going to be used.
100    ///
101    /// The various arguments here are:
102    ///
103    /// * `translation` - the core wasm translation that's being completed.
104    ///
105    /// * `funcs` - compilation metadata about functions within the translation
106    ///   as well as where the functions are located in the text section and any
107    ///   associated trampolines.
108    ///
109    /// * `wasm_to_array_trampolines` - list of all trampolines necessary for
110    ///   Wasm callers calling array callees (e.g. `Func::wrap`). One for each
111    ///   function signature in the module. Must be sorted by `SignatureIndex`.
112    ///
113    /// Returns the `CompiledModuleInfo` corresponding to this core Wasm module
114    /// as a result of this append operation. This is then serialized into the
115    /// final artifact by the caller.
116    pub fn append(&mut self, translation: ModuleTranslation<'_>) -> Result<CompiledModuleInfo> {
117        let ModuleTranslation {
118            mut module,
119            debuginfo,
120            has_unparsed_debuginfo,
121            data,
122            data_align,
123            passive_data,
124            wasm,
125            ..
126        } = translation;
127
128        // Place all data from the wasm module into a section which will the
129        // source of the data later at runtime. This additionally keeps track of
130        // the offset of
131        let mut total_data_len = 0;
132        let data_offset = self
133            .obj
134            .append_section_data(self.data, &[], data_align.unwrap_or(1));
135        for (i, data) in data.iter().enumerate() {
136            // The first data segment has its alignment specified as the alignment
137            // for the entire section, but everything afterwards is adjacent so it
138            // has alignment of 1.
139            let align = if i == 0 { data_align.unwrap_or(1) } else { 1 };
140            self.obj.append_section_data(self.data, data, align);
141            total_data_len += data.len();
142        }
143        for data in passive_data.iter() {
144            self.obj.append_section_data(self.data, data, 1);
145        }
146
147        // If any names are present in the module then the `ELF_NAME_DATA` section
148        // is create and appended.
149        let mut func_names = Vec::new();
150        if debuginfo.name_section.func_names.len() > 0 {
151            let name_id = *self.names.get_or_insert_with(|| {
152                self.obj.add_section(
153                    self.obj.segment_name(StandardSegment::Data).to_vec(),
154                    obj::ELF_NAME_DATA.as_bytes().to_vec(),
155                    SectionKind::ReadOnlyData,
156                )
157            });
158            let mut sorted_names = debuginfo.name_section.func_names.iter().collect::<Vec<_>>();
159            sorted_names.sort_by_key(|(idx, _name)| *idx);
160            for (idx, name) in sorted_names {
161                let offset = self.obj.append_section_data(name_id, name.as_bytes(), 1);
162                let offset = match u32::try_from(offset) {
163                    Ok(offset) => offset,
164                    Err(_) => bail!("name section too large (> 4gb)"),
165                };
166                let len = u32::try_from(name.len()).unwrap();
167                func_names.push(FunctionName {
168                    idx: *idx,
169                    offset,
170                    len,
171                });
172            }
173        }
174
175        // Data offsets in `MemoryInitialization` are offsets within the
176        // `translation.data` list concatenated which is now present in the data
177        // segment that's appended to the object. Increase the offsets by
178        // `self.data_size` to account for any previously added module.
179        let data_offset = u32::try_from(data_offset).unwrap();
180        match &mut module.memory_initialization {
181            MemoryInitialization::Segmented(list) => {
182                for segment in list {
183                    segment.data.start = segment.data.start.checked_add(data_offset).unwrap();
184                    segment.data.end = segment.data.end.checked_add(data_offset).unwrap();
185                }
186            }
187            MemoryInitialization::Static { map } => {
188                for (_, segment) in map {
189                    if let Some(segment) = segment {
190                        segment.data.start = segment.data.start.checked_add(data_offset).unwrap();
191                        segment.data.end = segment.data.end.checked_add(data_offset).unwrap();
192                    }
193                }
194            }
195        }
196
197        // Data offsets for passive data are relative to the start of
198        // `translation.passive_data` which was appended to the data segment
199        // of this object, after active data in `translation.data`. Update the
200        // offsets to account prior modules added in addition to active data.
201        let data_offset = data_offset + u32::try_from(total_data_len).unwrap();
202        for (_, range) in module.passive_data_map.iter_mut() {
203            range.start = range.start.checked_add(data_offset).unwrap();
204            range.end = range.end.checked_add(data_offset).unwrap();
205        }
206
207        // Insert the wasm raw wasm-based debuginfo into the output, if
208        // requested. Note that this is distinct from the native debuginfo
209        // possibly generated by the native compiler, hence these sections
210        // getting wasm-specific names.
211        let mut dwarf = Vec::new();
212        if self.tunables.parse_wasm_debuginfo {
213            self.push_debuginfo(&mut dwarf, &debuginfo);
214        }
215
216        Ok(CompiledModuleInfo {
217            module,
218            func_names,
219            meta: Metadata {
220                has_unparsed_debuginfo,
221                code_section_offset: debuginfo.wasm_file.code_section_offset,
222                has_wasm_debuginfo: self.tunables.parse_wasm_debuginfo,
223                dwarf,
224            },
225            checksum: WasmChecksum::from_binary(wasm, self.tunables.recording),
226        })
227    }
228
229    fn push_debug<'b, T>(&mut self, dwarf: &mut Vec<(u8, Range<u64>)>, section: &T)
230    where
231        T: gimli::Section<gimli::EndianSlice<'b, gimli::LittleEndian>>,
232    {
233        let data = section.reader().slice();
234        if data.is_empty() {
235            return;
236        }
237        let section_id = *self.dwarf.get_or_insert_with(|| {
238            self.obj.add_section(
239                self.obj.segment_name(StandardSegment::Debug).to_vec(),
240                obj::ELF_WASMTIME_DWARF.as_bytes().to_vec(),
241                SectionKind::Debug,
242            )
243        });
244        let offset = self.obj.append_section_data(section_id, data, 1);
245        dwarf.push((T::id() as u8, offset..offset + data.len() as u64));
246    }
247
248    /// Creates the `ELF_WASMTIME_INFO` section from the given serializable data
249    /// structure.
250    pub fn serialize_info<T>(&mut self, info: &T)
251    where
252        T: serde::Serialize,
253    {
254        let section = self.obj.add_section(
255            self.obj.segment_name(StandardSegment::Data).to_vec(),
256            obj::ELF_WASMTIME_INFO.as_bytes().to_vec(),
257            SectionKind::ReadOnlyData,
258        );
259        let data = postcard::to_allocvec(info).unwrap();
260        self.obj.set_section_data(section, data, 1);
261    }
262
263    /// Serializes `self` into a buffer. This can be used for execution as well
264    /// as serialization.
265    pub fn finish<T: WritableBuffer>(self, t: &mut T) -> Result<()> {
266        self.obj.emit(t).map_err(|e| e.into())
267    }
268}
269
270/// A type which can be the result of serializing an object.
271pub trait FinishedObject: Sized {
272    /// State required for `finish_object`, if any.
273    type State;
274
275    /// Emit the object as `Self`.
276    fn finish_object(obj: ObjectBuilder<'_>, state: &Self::State) -> Result<Self>;
277}
278
279impl FinishedObject for Vec<u8> {
280    type State = ();
281    fn finish_object(obj: ObjectBuilder<'_>, _state: &Self::State) -> Result<Self> {
282        let mut result = ObjectVec::default();
283        obj.finish(&mut result)?;
284        return Ok(result.0);
285
286        #[derive(Default)]
287        struct ObjectVec(Vec<u8>);
288
289        impl WritableBuffer for ObjectVec {
290            fn len(&self) -> usize {
291                self.0.len()
292            }
293
294            fn reserve(&mut self, additional: usize) -> Result<(), ()> {
295                assert_eq!(self.0.len(), 0, "cannot reserve twice");
296                self.0 = Vec::with_capacity(additional);
297                Ok(())
298            }
299
300            fn resize(&mut self, new_len: usize) {
301                if new_len <= self.0.len() {
302                    self.0.truncate(new_len)
303                } else {
304                    self.0.extend(vec![0; new_len - self.0.len()])
305                }
306            }
307
308            fn write_bytes(&mut self, val: &[u8]) {
309                self.0.extend(val);
310            }
311        }
312    }
313}
wasmtime_environ/compile/module_artifacts.rs

wasmtime_environ/compile/
module_artifacts.rs
