Move allocation functions into javy lib (#461)

* Move allocation functions into javy lib

* Update crates/javy/src/alloc.rs

Co-authored-by: Saúl Cabrera <saulecabrera@gmail.com>

* Add comment about cfg_attr usage

* teh -> the

---------

Co-authored-by: Saúl Cabrera <saulecabrera@gmail.com>

Cargo.toml

@@ -21,7 +21,7 @@ wasmtime-wasi = "9.0"
 wasi-common = "9.0"
 anyhow = "1.0"
 once_cell = "1.16"
-javy = { path = "crates/javy", version = "2.0.1-alpha.1" }
+javy = { path = "crates/javy", version = "2.1.0-alpha.1" }
 
 [profile.release]
 lto = true

crates/apis/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "javy-apis"
-version = "2.0.1-alpha.1"
+version = "2.1.0-alpha.1"
 authors.workspace = true
 edition.workspace = true
 license.workspace = true

crates/cli/src/wasm_generator/static.rs

@@ -45,19 +45,21 @@ pub fn generate(js: &JS, exports: Vec<Export>) -> Result<Vec<u8>> {
 
     let mut module = transform::module_config().parse(&wasm)?;
 
-    let (realloc, invoke, memory) = {
+    let (realloc, free, invoke, memory) = {
         let mut exports = HashMap::new();
         for export in module.exports.iter() {
             exports.insert(export.name.as_str(), export);
         }
         (
             *exports.get("canonical_abi_realloc").unwrap(),
+            *exports.get("canonical_abi_free").unwrap(),
             *exports.get("javy.invoke").unwrap(),
             *exports.get("memory").unwrap(),
         )
     };
 
     let realloc_export = realloc.id();
+    let free_export = free.id();
     let invoke_export = invoke.id();
 
     if !exports.is_empty() {
@@ -75,6 +77,7 @@ pub fn generate(js: &JS, exports: Vec<Export>) -> Result<Vec<u8>> {
 
     // We no longer need these exports so remove them.
     module.exports.delete(realloc_export);
+    module.exports.delete(free_export);
     module.exports.delete(invoke_export);
 
     let wasm = module.emit_wasm();

crates/core/Cargo.toml

@@ -15,7 +15,7 @@ crate-type = ["cdylib"]
 
 [dependencies]
 anyhow = { workspace = true }
-javy = { workspace = true }
+javy = { workspace = true, features = ["export_alloc_fns"] }
 javy-apis = { path = "../apis", features = ["console", "text_encoding", "random", "stream_io"] }
 once_cell = { workspace = true }
 

crates/core/src/lib.rs

@@ -3,7 +3,6 @@ use once_cell::sync::OnceCell;
 use std::slice;
 use std::str;
 
-mod alloc;
 mod execution;
 mod runtime;
 
@@ -83,39 +82,3 @@ pub unsafe extern "C" fn invoke(
     execution::run_bytecode(runtime, bytecode);
     execution::invoke_function(runtime, FUNCTION_MODULE_NAME, fn_name);
 }
-
-/// 1. Allocate memory of new_size with alignment.
-/// 2. If original_ptr != 0
-///   a. copy min(new_size, original_size) bytes from original_ptr to new memory
-///   b. de-allocate original_ptr
-/// 3. return new memory ptr
-///
-/// # Safety
-///
-/// * `original_ptr` must be 0 or a valid pointer
-/// * if `original_ptr` is not 0, it must be valid for reads of `original_size`
-///   bytes
-/// * if `original_ptr` is not 0, it must be properly aligned
-/// * if `original_size` is not 0, it must match the `new_size` value provided
-///   in the original `canonical_abi_realloc` call that returned `original_ptr`
-#[export_name = "canonical_abi_realloc"]
-pub unsafe extern "C" fn canonical_abi_realloc(
-    original_ptr: *mut u8,
-    original_size: usize,
-    alignment: usize,
-    new_size: usize,
-) -> *mut std::ffi::c_void {
-    alloc::canonical_abi_realloc(original_ptr, original_size, alignment, new_size)
-}
-
-/// Frees memory
-///
-/// # Safety
-///
-/// * `ptr` must denote a block of memory allocated by `canonical_abi_realloc`
-/// * `size` and `alignment` must match the values provided in the original
-///   `canonical_abi_realloc` call that returned `ptr`
-#[export_name = "canonical_abi_free"]
-pub unsafe extern "C" fn canonical_abi_free(ptr: *mut u8, size: usize, alignment: usize) {
-    alloc::canonical_abi_free(ptr, size, alignment)
-}

crates/core/src/main.rs

@@ -5,7 +5,6 @@ use std::slice;
 use std::str;
 use std::string::String;
 
-mod alloc;
 mod execution;
 mod runtime;
 
@@ -37,31 +36,6 @@ fn main() {
     execution::run_bytecode(&runtime, &bytecode);
 }
 
-// Removed in post_processing.
-/// 1. Allocate memory of new_size with alignment.
-/// 2. If original_ptr != 0
-///   a. copy min(new_size, original_size) bytes from original_ptr to new memory
-///   b. de-allocate original_ptr
-/// 3. return new memory ptr
-///
-/// # Safety
-///
-/// * `original_ptr` must be 0 or a valid pointer
-/// * if `original_ptr` is not 0, it must be valid for reads of `original_size`
-///   bytes
-/// * if `original_ptr` is not 0, it must be properly aligned
-/// * if `original_size` is not 0, it must match the `new_size` value provided
-///   in the original `canonical_abi_realloc` call that returned `original_ptr`
-#[export_name = "canonical_abi_realloc"]
-pub unsafe extern "C" fn canonical_abi_realloc(
-    original_ptr: *mut u8,
-    original_size: usize,
-    alignment: usize,
-    new_size: usize,
-) -> *mut std::ffi::c_void {
-    alloc::canonical_abi_realloc(original_ptr, original_size, alignment, new_size)
-}
-
 // Removed in post-processing.
 /// Evaluates QuickJS bytecode and invokes the exported JS function name.
 ///

crates/javy/CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Added
+
+- `alloc` module containing implementations of a realloc function and a free function.
+- An `export_alloc_fns` crate feature which when enabled, will export `canonical_abi_realloc` and `canonical_abi_free`
+  functions from your Wasm module.
+
 ## 2.0.0 - 2023-08-17
 
 ### Changed

crates/javy/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "javy"
-version = "2.0.1-alpha.1"
+version = "2.1.0-alpha.1"
 authors.workspace = true
 edition.workspace = true
 license.workspace = true
@@ -17,5 +17,6 @@ serde-transcode = { version = "1.1", optional = true }
 rmp-serde = { version = "^1.1", optional = true }
 
 [features]
+export_alloc_fns = []
 messagepack = ["rmp-serde", "serde-transcode"]
 json = ["serde_json", "serde-transcode"]

crates/javy/src/alloc.rs

@@ -0,0 +1,65 @@
+use std::alloc::{alloc, dealloc, Layout};
+use std::ptr::copy_nonoverlapping;
+
+// Unlike C's realloc, zero-length allocations need not have
+// unique addresses, so a zero-length allocation may be passed
+// in and also requested, but it's ok to return anything that's
+// non-zero to indicate success.
+const ZERO_SIZE_ALLOCATION_PTR: *mut u8 = 1 as _;
+
+// For canonical_abi_realloc and canonical_abi_free, we want the functions to be available for use
+// by other crates, whether or not the `export_alloc_fns` feature is enabled. When the
+// `export_alloc_fns` feature is enabled, we also want to export the two functions from the Wasm
+// module. To do that, we apply an `export_name` attribute when the `export_alloc_fns` feature is
+// enabled. The `export_name` attribute is what causes the functions to be exported from the Wasm
+// module as opposed to just exported for use by other crates.
+
+/// 1. Allocate memory of new_size with alignment.
+/// 2. If original_ptr != 0
+///   a. copy min(new_size, original_size) bytes from original_ptr to new memory
+///   b. de-allocate original_ptr
+/// 3. Return new memory ptr.
+///
+/// # Safety
+///
+/// * `original_ptr` must be 0 or a valid pointer
+/// * if `original_ptr` is not 0, it must be valid for reads of `original_size`
+///   bytes
+/// * if `original_ptr` is not 0, it must be properly aligned
+/// * if `original_size` is not 0, it must match the `new_size` value provided
+///   in the original `canonical_abi_realloc` call that returned `original_ptr`
+#[cfg_attr(feature = "export_alloc_fns", export_name = "canonical_abi_realloc")]
+pub unsafe extern "C" fn canonical_abi_realloc(
+    original_ptr: *mut u8,
+    original_size: usize,
+    alignment: usize,
+    new_size: usize,
+) -> *mut std::ffi::c_void {
+    assert!(new_size >= original_size);
+
+    let new_mem = match new_size {
+        0 => ZERO_SIZE_ALLOCATION_PTR,
+        // this call to `alloc` is safe since `new_size` must be > 0
+        _ => alloc(Layout::from_size_align(new_size, alignment).unwrap()),
+    };
+
+    if !original_ptr.is_null() && original_size != 0 {
+        copy_nonoverlapping(original_ptr, new_mem, original_size);
+        canonical_abi_free(original_ptr, original_size, alignment);
+    }
+    new_mem as _
+}
+
+/// Frees memory
+///
+/// # Safety
+///
+/// * `ptr` must denote a block of memory allocated by `canonical_abi_realloc`
+/// * `size` and `alignment` must match the values provided in the original
+///   `canonical_abi_realloc` call that returned `ptr`
+#[cfg_attr(feature = "export_alloc_fns", export_name = "canonical_abi_free")]
+pub unsafe extern "C" fn canonical_abi_free(ptr: *mut u8, size: usize, alignment: usize) {
+    if size > 0 {
+        dealloc(ptr, Layout::from_size_align(size, alignment).unwrap())
+    };
+}

crates/javy/src/lib.rs

@@ -40,6 +40,7 @@ pub use config::Config;
 pub use quickjs_wasm_rs as quickjs;
 pub use runtime::Runtime;
 
+pub mod alloc;
 mod config;
 mod runtime;