[−][src]Module wasmtime_runtime::libcalls

Runtime library calls.

Note that Wasm compilers may sometimes perform these inline rather than calling them, particularly when CPUs have special instructions which compute them directly.

These functions are called by compiled Wasm code, and therefore must take certain care about some things:

They must always be pub extern "C" and should only contain basic, raw i32/i64/f32/f64/pointer parameters that are safe to pass across the system ABI!
If any nested function propagates an Err(trap) out to the library function frame, we need to raise it. This involves some nasty and quite unsafe code under the covers! Notable, after raising the trap, drops will not be run for local variables! This can lead to things like leaking InstanceHandles which leads to never deallocating JIT code, instances, and modules! Therefore, always use nested blocks to ensure drops run before raising a trap:

ⓘ
```
pub extern "C" fn my_lib_function(...) {
    let result = {
        // Do everything in here so drops run at the end of the block.
        ...
    };
    if let Err(trap) = result {
        // Now we can safely raise the trap without leaking!
        raise_lib_trap(trap);
    }
}
```

When receiving a raw *mut u8 that is actually a VMExternRef reference, convert it into a proper VMExternRef with VMExternRef::clone_from_raw as soon as apossible. Any GC before raw pointer is converted into a reference can potentially collect the referenced object, which could lead to use after free. Avoid this by eagerly converting into a proper VMExternRef!

pub unsafe extern "C" my_lib_takes_ref(raw_extern_ref: *mut u8) {
    // Before `clone_from_raw`, `raw_extern_ref` is potentially unrooted,
    // and doing GC here could lead to use after free!

    let my_extern_ref = if raw_extern_ref.is_null() {
        None
    } else {
        Some(VMExternRef::clone_from_raw(raw_extern_ref))
    };

    // Now that we did `clone_from_raw`, it is safe to do a GC (or do
    // anything else that might transitively GC, like call back into
    // Wasm!)
}

Functions

wasmtime_activations_table_insert_with_gc ^⚠	Do a GC and insert the given `externref` into the `VMExternRefActivationsTable`.
wasmtime_data_drop ^⚠	Implementation of `data.drop`.
wasmtime_drop_externref ^⚠	Drop a `VMExternRef`.
wasmtime_elem_drop ^⚠	Implementation of `elem.drop`.
wasmtime_externref_global_get ^⚠	Perform a Wasm `global.get` for `externref` globals.
wasmtime_externref_global_set ^⚠	Perform a Wasm `global.set` for `externref` globals.
wasmtime_f32_ceil	Implementation of f32.ceil
wasmtime_f32_floor	Implementation of f32.floor
wasmtime_f32_nearest	Implementation of f32.nearest
wasmtime_f32_trunc	Implementation of f32.trunc
wasmtime_f64_ceil	Implementation of f64.ceil
wasmtime_f64_floor	Implementation of f64.floor
wasmtime_f64_nearest	Implementation of f64.nearest
wasmtime_f64_trunc	Implementation of f64.trunc
wasmtime_i64_ishl	Implementation of i64.ishl
wasmtime_i64_sdiv	Implementation of i64.sdiv
wasmtime_i64_srem	Implementation of i64.srem
wasmtime_i64_sshr	Implementation of i64.sshr
wasmtime_i64_udiv	Implementation of i64.udiv
wasmtime_i64_urem	Implementation of i64.urem
wasmtime_i64_ushr	Implementation of i64.ushr
wasmtime_imported_memory32_grow ^⚠	Implementation of memory.grow for imported 32-bit memories.
wasmtime_imported_memory32_size ^⚠	Implementation of memory.size for imported 32-bit memories.
wasmtime_imported_memory_fill ^⚠	Implementation of `memory.fill` for imported memories.
wasmtime_memory32_grow ^⚠	Implementation of memory.grow for locally-defined 32-bit memories.
wasmtime_memory32_size ^⚠	Implementation of memory.size for locally-defined 32-bit memories.
wasmtime_memory_copy ^⚠	Implementation of `memory.copy` for locally defined memories.
wasmtime_memory_fill ^⚠	Implementation of `memory.fill` for locally defined memories.
wasmtime_memory_init ^⚠	Implementation of `memory.init`.
wasmtime_table_copy ^⚠	Implementation of `table.copy`.
wasmtime_table_fill ^⚠	Implementation of `table.fill`.
wasmtime_table_grow ^⚠	Implementation of `table.grow`.
wasmtime_table_init ^⚠	Implementation of `table.init`.