Merge #335

335: allow resize_heap to grow heap in emscripten r=syrusakbary a=MarkMcCaskey

Emscripten programs compiled with `-s ALLOW_MEMORY_GROWTH=1` will now work

Co-authored-by: Mark McCaskey <mark@wasmer.io>

lib/emscripten/src/memory.rs

@@ -1,6 +1,9 @@
 use super::process::abort_with_message;
 use libc::{c_int, c_void, memcpy, size_t};
-use wasmer_runtime_core::vm::Ctx;
+use wasmer_runtime_core::{
+    units::{Pages, WASM_MAX_PAGES, WASM_MIN_PAGES, WASM_PAGE_SIZE},
+    vm::Ctx,
+};
 
 /// emscripten: _emscripten_memcpy_big
 pub fn _emscripten_memcpy_big(ctx: &mut Ctx, dest: u32, src: u32, len: u32) -> u32 {
@@ -22,11 +25,41 @@ pub fn _emscripten_get_heap_size(ctx: &mut Ctx) -> u32 {
     ctx.memory(0).size().bytes().0 as u32
 }
 
+// From emscripten implementation
+fn align_up(mut val: usize, multiple: usize) -> usize {
+    if val % multiple > 0 {
+        val += multiple - val % multiple;
+    }
+    val
+}
+
 /// emscripten: _emscripten_resize_heap
-pub fn _emscripten_resize_heap(_ctx: &mut Ctx, _requested_size: u32) -> u32 {
-    debug!("emscripten::_emscripten_resize_heap {}", _requested_size);
-    // TODO: Fix implementation
-    0
+/// Note: this function only allows growing the size of heap
+pub fn _emscripten_resize_heap(ctx: &mut Ctx, requested_size: u32) -> u32 {
+    debug!("emscripten::_emscripten_resize_heap {}", requested_size);
+    let current_memory_pages = ctx.memory(0).size();
+    let current_memory = current_memory_pages.bytes().0 as u32;
+
+    // implementation from emscripten
+    let mut new_size = usize::max(current_memory as usize, WASM_MIN_PAGES * WASM_PAGE_SIZE);
+    while new_size < requested_size as usize {
+        if new_size <= 0x2000_0000 {
+            new_size = align_up(new_size * 2, WASM_PAGE_SIZE);
+        } else {
+            new_size = usize::min(
+                align_up((3 * new_size + 0x8000_0000) / 4, WASM_PAGE_SIZE),
+                WASM_PAGE_SIZE * WASM_MAX_PAGES,
+            );
+        }
+    }
+
+    let amount_to_grow = (new_size - current_memory as usize) / WASM_PAGE_SIZE;
+    if let Ok(_pages_allocated) = ctx.memory(0).grow(Pages(amount_to_grow as u32)) {
+        debug!("{} pages allocated", _pages_allocated.0);
+        1
+    } else {
+        0
+    }
 }
 
 /// emscripten: getTotalMemory

lib/runtime-core/src/units.rs

@@ -4,8 +4,10 @@ use std::{
     ops::{Add, Sub},
 };
 
-const WASM_PAGE_SIZE: usize = 65_536;
-const WASM_MAX_PAGES: usize = 65_536;
+pub const WASM_PAGE_SIZE: usize = 65_536;
+pub const WASM_MAX_PAGES: usize = 65_536;
+// From emscripten resize_heap implementation
+pub const WASM_MIN_PAGES: usize = 256;
 
 /// Units of WebAssembly pages (as specified to be 65,536 bytes).
 #[derive(Serialize, Deserialize, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]