wasmtime/trampoline/

memory.rs

use crate::memory::{LinearMemory, MemoryCreator};
use crate::module::BareModuleInfo;
use crate::store::{InstanceId, StoreOpaque};
use crate::MemoryType;
use anyhow::{anyhow, Result};
use std::convert::TryFrom;
use std::ops::Range;
use std::sync::Arc;
use wasmtime_environ::{
    DefinedMemoryIndex, DefinedTableIndex, EntityIndex, MemoryPlan, MemoryStyle, Module,
    PrimaryMap, WASM_PAGE_SIZE,
};
use wasmtime_runtime::{
    CompiledModuleId, Imports, InstanceAllocationRequest, InstanceAllocator, Memory, MemoryImage,
    OnDemandInstanceAllocator, RuntimeLinearMemory, RuntimeMemoryCreator, SharedMemory, StorePtr,
    Table, VMMemoryDefinition,
};

/// Create a "frankenstein" instance with a single memory.
///
/// This separate instance is necessary because Wasm objects in Wasmtime must be
/// attached to instances (versus the store, e.g.) and some objects exist
/// outside: a host-provided memory import, shared memory.
pub fn create_memory(
    store: &mut StoreOpaque,
    memory_ty: &MemoryType,
    preallocation: Option<&SharedMemory>,
) -> Result<InstanceId> {
    let mut module = Module::new();

    // Create a memory plan for the memory, though it will never be used for
    // constructing a memory with an allocator: instead the memories are either
    // preallocated (i.e., shared memory) or allocated manually below.
    let plan = wasmtime_environ::MemoryPlan::for_memory(
        memory_ty.wasmtime_memory().clone(),
        &store.engine().config().tunables,
    );
    let memory_id = module.memory_plans.push(plan.clone());

    // Since we have only associated a single memory with the "frankenstein"
    // instance, it will be exported at index 0.
    debug_assert_eq!(memory_id.as_u32(), 0);
    module
        .exports
        .insert(String::new(), EntityIndex::Memory(memory_id));

    // We create an instance in the on-demand allocator when creating handles
    // associated with external objects. The configured instance allocator
    // should only be used when creating module instances as we don't want host
    // objects to count towards instance limits.
    let runtime_info = &BareModuleInfo::maybe_imported_func(Arc::new(module), None).into_traitobj();
    let host_state = Box::new(());
    let imports = Imports::default();
    let request = InstanceAllocationRequest {
        imports,
        host_state,
        store: StorePtr::new(store.traitobj()),
        runtime_info,
    };

    unsafe {
        let handle = SingleMemoryInstance {
            preallocation,
            ondemand: OnDemandInstanceAllocator::default(),
        }
        .allocate(request)?;
        let instance_id = store.add_instance(handle.clone(), true);
        Ok(instance_id)
    }
}

struct LinearMemoryProxy {
    mem: Box<dyn LinearMemory>,
}

impl RuntimeLinearMemory for LinearMemoryProxy {
    fn byte_size(&self) -> usize {
        self.mem.byte_size()
    }

    fn maximum_byte_size(&self) -> Option<usize> {
        self.mem.maximum_byte_size()
    }

    fn grow_to(&mut self, new_size: usize) -> Result<()> {
        self.mem.grow_to(new_size)
    }

    fn vmmemory(&mut self) -> VMMemoryDefinition {
        VMMemoryDefinition {
            base: self.mem.as_ptr(),
            current_length: self.mem.byte_size().into(),
        }
    }

    fn needs_init(&self) -> bool {
        true
    }

    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
        self
    }

    fn wasm_accessible(&self) -> Range<usize> {
        self.mem.wasm_accessible()
    }
}

#[derive(Clone)]
pub(crate) struct MemoryCreatorProxy(pub Arc<dyn MemoryCreator>);

impl RuntimeMemoryCreator for MemoryCreatorProxy {
    fn new_memory(
        &self,
        plan: &MemoryPlan,
        minimum: usize,
        maximum: Option<usize>,
        _: Option<&Arc<MemoryImage>>,
    ) -> Result<Box<dyn RuntimeLinearMemory>> {
        let ty = MemoryType::from_wasmtime_memory(&plan.memory);
        let reserved_size_in_bytes = match plan.style {
            MemoryStyle::Static { bound } => {
                Some(usize::try_from(bound * (WASM_PAGE_SIZE as u64)).unwrap())
            }
            MemoryStyle::Dynamic { .. } => None,
        };
        self.0
            .new_memory(
                ty,
                minimum,
                maximum,
                reserved_size_in_bytes,
                usize::try_from(plan.offset_guard_size).unwrap(),
            )
            .map(|mem| Box::new(LinearMemoryProxy { mem }) as Box<dyn RuntimeLinearMemory>)
            .map_err(|e| anyhow!(e))
    }
}

struct SingleMemoryInstance<'a> {
    preallocation: Option<&'a SharedMemory>,
    ondemand: OnDemandInstanceAllocator,
}

unsafe impl InstanceAllocator for SingleMemoryInstance<'_> {
    fn allocate_index(&self, req: &InstanceAllocationRequest) -> Result<usize> {
        self.ondemand.allocate_index(req)
    }

    fn deallocate_index(&self, index: usize) {
        self.ondemand.deallocate_index(index)
    }

    fn allocate_memories(
        &self,
        index: usize,
        req: &mut InstanceAllocationRequest,
        mem: &mut PrimaryMap<DefinedMemoryIndex, Memory>,
    ) -> Result<()> {
        assert_eq!(req.runtime_info.module().memory_plans.len(), 1);
        match self.preallocation {
            Some(shared_memory) => {
                mem.push(shared_memory.clone().as_memory());
            }
            None => {
                self.ondemand.allocate_memories(index, req, mem)?;
            }
        }
        Ok(())
    }

    fn deallocate_memories(&self, index: usize, mems: &mut PrimaryMap<DefinedMemoryIndex, Memory>) {
        self.ondemand.deallocate_memories(index, mems)
    }

    fn allocate_tables(
        &self,
        index: usize,
        req: &mut InstanceAllocationRequest,
        tables: &mut PrimaryMap<DefinedTableIndex, Table>,
    ) -> Result<()> {
        self.ondemand.allocate_tables(index, req, tables)
    }

    fn deallocate_tables(&self, index: usize, tables: &mut PrimaryMap<DefinedTableIndex, Table>) {
        self.ondemand.deallocate_tables(index, tables)
    }

    #[cfg(feature = "async")]
    fn allocate_fiber_stack(&self) -> Result<wasmtime_fiber::FiberStack> {
        unreachable!()
    }

    #[cfg(feature = "async")]
    unsafe fn deallocate_fiber_stack(&self, _stack: &wasmtime_fiber::FiberStack) {
        unreachable!()
    }

    fn purge_module(&self, _: CompiledModuleId) {
        unreachable!()
    }
}