Add test for custom host memory

Signed-off-by: Tyler Rockwood <rockwood@redpanda.com>

tests/all/main.rs

@@ -30,6 +30,7 @@ mod module_serialize;
 mod name;
 mod pooling_allocator;
 mod relocs;
+mod stack_creator;
 mod stack_overflow;
 mod store;
 mod table;

tests/all/stack_creator.rs

@@ -0,0 +1,156 @@
+#[cfg(all(not(target_os = "windows"), not(miri)))]
+mod not_for_windows {
+    use anyhow::{bail, Context};
+    use std::{
+        alloc::{GlobalAlloc, Layout, System},
+        ops::Range,
+        ptr::NonNull,
+        sync::Arc,
+    };
+    use wasmtime::*;
+
+    fn align_up(v: usize, align: usize) -> usize {
+        return (v + (align - 1)) & (!(align - 1));
+    }
+
+    struct CustomStack {
+        base: NonNull<u8>,
+        len: usize,
+    }
+    unsafe impl Send for CustomStack {}
+    unsafe impl Sync for CustomStack {}
+    impl CustomStack {
+        fn new(base: NonNull<u8>, len: usize) -> Self {
+            CustomStack { base, len }
+        }
+    }
+    unsafe impl StackMemory for CustomStack {
+        fn top(&self) -> *mut u8 {
+            unsafe { self.base.as_ptr().add(self.len) }
+        }
+        fn range(&self) -> Range<usize> {
+            let base = self.base.as_ptr() as usize;
+            base..base + self.len
+        }
+    }
+
+    // A creator that allocates stacks on the heap instead of mmap'ing.
+    struct CustomStackCreator {
+        memory: NonNull<u8>,
+        size: usize,
+        layout: Layout,
+    }
+
+    unsafe impl Send for CustomStackCreator {}
+    unsafe impl Sync for CustomStackCreator {}
+    impl CustomStackCreator {
+        fn new() -> Result<Self> {
+            // 1MB
+            const MINIMUM_STACK_SIZE: usize = 1 * 1_024 * 1_024;
+            let page_size = rustix::param::page_size();
+            let size = align_up(MINIMUM_STACK_SIZE, page_size);
+            // Add an extra page for the guard page
+            let layout = Layout::from_size_align(size + page_size, page_size)
+                .context("unable to compute stack layout")?;
+            let memory = unsafe {
+                let mem = System.alloc(layout);
+                let notnull = NonNull::new(mem);
+                if let Some(mem) = notnull {
+                    // Mark guard page as protected
+                    rustix::mm::mprotect(
+                        mem.as_ptr().cast(),
+                        page_size,
+                        rustix::mm::MprotectFlags::empty(),
+                    )?;
+                }
+                notnull
+            }
+            .context("unable to allocate stack memory")?;
+            Ok(CustomStackCreator {
+                memory,
+                size,
+                layout,
+            })
+        }
+        fn range(&self) -> Range<usize> {
+            let page_size = rustix::param::page_size();
+            let base = unsafe { self.memory.as_ptr().add(page_size) as usize };
+            base..base + self.size
+        }
+    }
+    impl Drop for CustomStackCreator {
+        fn drop(&mut self) {
+            let page_size = rustix::param::page_size();
+            unsafe {
+                // Unprotect the guard page as the allocator could reuse it.
+                rustix::mm::mprotect(
+                    self.memory.as_ptr().cast(),
+                    page_size,
+                    rustix::mm::MprotectFlags::READ | rustix::mm::MprotectFlags::WRITE,
+                ).unwrap();
+                System.dealloc(self.memory.as_ptr(), self.layout);
+            }
+        }
+    }
+    unsafe impl StackCreator for CustomStackCreator {
+        fn new_stack(&self, size: usize) -> Result<Box<dyn StackMemory>> {
+            if size != self.size {
+                bail!("must use the size we allocated for this stack memory creator");
+            }
+            let page_size = rustix::param::page_size();
+            // skip over the page size
+            let base_ptr = unsafe { self.memory.as_ptr().add(page_size) };
+            let base = NonNull::new(base_ptr).context("unable to compute stack base")?;
+            Ok(Box::new(CustomStack::new(base, self.size)))
+        }
+    }
+
+    fn config() -> (Store<()>, Arc<CustomStackCreator>) {
+        let stack_creator = Arc::new(CustomStackCreator::new().unwrap());
+        let mut config = Config::new();
+        config
+            .async_support(true)
+            .max_wasm_stack(stack_creator.size / 2)
+            .async_stack_size(stack_creator.size)
+            .with_host_stack(stack_creator.clone());
+        (
+            Store::new(&Engine::new(&config).unwrap(), ()),
+            stack_creator,
+        )
+    }
+
+    #[tokio::test]
+    async fn called_on_custom_heap_stack() -> Result<()> {
+        let (mut store, stack_creator) = config();
+        let module = Module::new(
+            store.engine(),
+            r#"
+            (module
+                (import "host" "callback" (func $callback (result i64)))
+                (func $f (result i64) (call $callback))
+                (export "f" (func $f))
+            )
+        "#,
+        )?;
+
+        let ty = FuncType::new([], [ValType::I64]);
+        let host_func = Func::new(&mut store, ty, move |_caller, _params, results| {
+            let foo = 42;
+            // output an address on the stack
+            results[0] = Val::I64((&foo as *const i32) as usize as i64);
+            Ok(())
+        });
+        let export = wasmtime::Extern::Func(host_func);
+        let instance = Instance::new_async(&mut store, &module, &[export]).await?;
+        let mut results = [Val::I64(0)];
+        instance
+            .get_func(&mut store, "f")
+            .context("missing function export")?
+            .call_async(&mut store, &[], &mut results)
+            .await?;
+        // Make sure the stack address we wrote was within our custom stack range
+        let stack_address = results[0].i64().unwrap() as usize;
+        assert!(stack_creator.range().contains(&stack_address));
+        Ok(())
+    }
+}