Struct wasmtime_jit::CodeMemory

pub struct CodeMemory { /* private fields */ }

Management of executable memory within a MmapVec

This type consumes ownership of a region of memory and will manage the executable permissions of the contained JIT code as necessary.

Implementations

impl CodeMemory

pub fn new(mmap: MmapVec) -> Result<Self>

Creates a new CodeMemory by taking ownership of the provided MmapVec.

The returned CodeMemory manages the internal MmapVec and the publish method is used to actually make the memory executable.

pub fn mmap(&self) -> &MmapVec

Returns a reference to the underlying MmapVec this memory owns.

Examples found in repository

src/instantiate.rs (line 444)

    pub fn mmap(&self) -> &MmapVec {
        self.code_memory.mmap()
    }

pub fn text(&self) -> &[u8]

Returns the contents of the text section of the ELF executable this represents.

Examples found in repository

src/instantiate.rs (line 456)

    pub fn text(&self) -> &[u8] {
        self.code_memory.text()
    }

src/code_memory.rs (line 229)

    pub unsafe fn vmtrampoline(&self, loc: FunctionLoc) -> VMTrampoline {
        let ptr = self.text()[loc.start as usize..][..loc.length as usize].as_ptr();
        mem::transmute::<*const u8, VMTrampoline>(ptr)
    }

    /// Publishes the internal ELF image to be ready for execution.
    ///
    /// This method can only be called once and will panic if called twice. This
    /// will parse the ELF image from the original `MmapVec` and do everything
    /// necessary to get it ready for execution, including:
    ///
    /// * Change page protections from read/write to read/execute.
    /// * Register unwinding information with the OS
    ///
    /// After this function executes all JIT code should be ready to execute.
    pub fn publish(&mut self) -> Result<()> {
        assert!(!self.published);
        self.published = true;

        if self.text().is_empty() {
            return Ok(());
        }

        // The unsafety here comes from a few things:
        //
        // * We're actually updating some page protections to executable memory.
        //
        // * We're registering unwinding information which relies on the
        //   correctness of the information in the first place. This applies to
        //   both the actual unwinding tables as well as the validity of the
        //   pointers we pass in itself.
        unsafe {
            let text = self.text();

            // Clear the newly allocated code from cache if the processor requires it
            //
            // Do this before marking the memory as R+X, technically we should be able to do it after
            // but there are some CPU's that have had errata about doing this with read only memory.
            icache_coherence::clear_cache(text.as_ptr().cast(), text.len())
                .expect("Failed cache clear");

            // Switch the executable portion from read/write to
            // read/execute, notably not using read/write/execute to prevent
            // modifications.
            self.mmap
                .make_executable(self.text.clone(), self.enable_branch_protection)
                .expect("unable to make memory executable");

            // Flush any in-flight instructions from the pipeline
            icache_coherence::pipeline_flush_mt().expect("Failed pipeline flush");

            // With all our memory set up use the platform-specific
            // `UnwindRegistration` implementation to inform the general
            // runtime that there's unwinding information available for all
            // our just-published JIT functions.
            self.register_unwind_info()?;
        }

        Ok(())
    }

    unsafe fn register_unwind_info(&mut self) -> Result<()> {
        if self.unwind.len() == 0 {
            return Ok(());
        }
        let text = self.text();
        let unwind_info = &self.mmap[self.unwind.clone()];
        let registration =
            UnwindRegistration::new(text.as_ptr(), unwind_info.as_ptr(), unwind_info.len())
                .context("failed to create unwind info registration")?;
        *self.unwind_registration = Some(registration);
        Ok(())
    }

pub fn dwarf_section(&self, section: SectionId) -> &[u8]

Returns the data in the corresponding dwarf section, or an empty slice if the section wasn’t present.

Examples found in repository

src/instantiate.rs (line 594)

    pub fn symbolize_context(&self) -> Result<Option<SymbolizeContext<'_>>> {
        use gimli::EndianSlice;
        if !self.meta.has_wasm_debuginfo {
            return Ok(None);
        }
        let dwarf = gimli::Dwarf::load(|id| -> Result<_> {
            let data = self.code_memory().dwarf_section(id);
            Ok(EndianSlice::new(data, gimli::LittleEndian))
        })?;
        let cx = addr2line::Context::from_dwarf(dwarf)
            .context("failed to create addr2line dwarf mapping context")?;
        Ok(Some(SymbolizeContext {
            inner: cx,
            code_section_offset: self.meta.code_section_offset,
        }))
    }

pub fn func_name_data(&self) -> &[u8]

Returns the data in the ELF_NAME_DATA section.

Examples found in repository

src/instantiate.rs (line 475)

    pub fn func_name(&self, idx: FuncIndex) -> Option<&str> {
        // Find entry for `idx`, if present.
        let i = self.func_names.binary_search_by_key(&idx, |n| n.idx).ok()?;
        let name = &self.func_names[i];

        // Here we `unwrap` the `from_utf8` but this can theoretically be a
        // `from_utf8_unchecked` if we really wanted since this section is
        // guaranteed to only have valid utf-8 data. Until it's a problem it's
        // probably best to double-check this though.
        let data = self.code_memory().func_name_data();
        Some(str::from_utf8(&data[name.offset as usize..][..name.len as usize]).unwrap())
    }

pub fn wasm_data(&self) -> &[u8]

Returns the concatenated list of all data associated with this wasm module.

This is used for initialization of memories and all data ranges stored in a Module are relative to the slice returned here.

pub fn address_map_data(&self) -> &[u8]

Returns the encoded address map section used to pass to wasmtime_environ::lookup_file_pos.

Examples found in repository

src/instantiate.rs (line 617)

    pub fn has_address_map(&self) -> bool {
        !self.code_memory.address_map_data().is_empty()
    }

pub fn wasmtime_info(&self) -> &[u8]

Returns the contents of the ELF_WASMTIME_INFO section, or an empty slice if it wasn’t found.

pub fn trap_data(&self) -> &[u8]

Returns the contents of the ELF_WASMTIME_TRAPS section, or an empty slice if it wasn’t found.

pub unsafe fn vmtrampoline(&self, loc: FunctionLoc) -> VMTrampoline

Returns a VMTrampoline function pointer for the given function in the text section.

Unsafety

This function is unsafe as there’s no guarantee that the returned function pointer is valid.

pub fn publish(&mut self) -> Result<()>

Publishes the internal ELF image to be ready for execution.

This method can only be called once and will panic if called twice. This will parse the ELF image from the original MmapVec and do everything necessary to get it ready for execution, including:

• Change page protections from read/write to read/execute.
• Register unwinding information with the OS

After this function executes all JIT code should be ready to execute.

Trait Implementations

impl Drop for CodeMemory

fn drop(&mut self)

Executes the destructor for this type.