Add no_std support (#122)

* add default-enabled std feature

* use parity-wasm/std feature only if std is enabled

* drop dependency on std::io

* use hashmap_core instead of std::collections::HashMap

* disable std::error in no_std

* core and alloc all the things

* mention no_std in readme

* add no_std feature and use hashmap_core only on no_std

* rename the no_std feature to core

* drop dependency on byteorder/std

* simplify float impl macro

* remove some trailing whitespace

* use libm for float math in no_std

* add note about no_std panics of libm to readme

* Embed nan-preserving-float crate.

* Add no_std check to the Travis CI config

* add missing dev-dependency

Author: Julius Rakow

.travis.yml

@@ -23,6 +23,8 @@ script:
 # Make sure nightly targets are not broken.
 - if [ "$TRAVIS_RUST_VERSION" == "nightly" ]; then cargo check --tests --manifest-path=fuzz/Cargo.toml; fi
 - if [ "$TRAVIS_RUST_VERSION" == "nightly" ]; then cargo check --benches --manifest-path=benches/Cargo.toml; fi
+# Make sure `no_std` version checks.
+- if [ "$TRAVIS_RUST_VERSION" == "nightly" ]; then cargo +nightly check --no-default-features --features core; fi
 - ./test.sh
 - ./doc.sh
 after_success: |

Cargo.toml

@@ -10,12 +10,22 @@ description = "WebAssembly interpreter"
 keywords = ["wasm", "webassembly", "bytecode", "interpreter"]
 exclude = [ "/res/*", "/tests/*", "/fuzz/*", "/benches/*" ]
 
+[features]
+default = ["std"]
+# Disable for no_std support
+std = ["parity-wasm/std", "byteorder/std"]
+# Enable for no_std support
+# hashmap_core only works on no_std
+core = ["hashmap_core", "libm"]
+
 [dependencies]
-parity-wasm = "0.31"
-byteorder = "1.0"
+parity-wasm = { version = "0.31", default-features = false }
+byteorder = { version = "1.0", default-features = false }
+hashmap_core = { version = "0.1.9", optional = true }
 memory_units = "0.3.0"
-nan-preserving-float = "0.1.0"
+libm = { version = "0.1.2", optional = true }
 
 [dev-dependencies]
 assert_matches = "1.1"
+rand = "0.4.2"
 wabt = "0.6"

README.md

@@ -27,6 +27,24 @@ cargo build
 cargo test
 ```
 
+# `no_std` support
+This crate supports `no_std` environments.
+Enable the `core` feature and disable default features:
+```toml
+[dependencies]
+parity-wasm = {
+	version = "0.31",
+	default-features = false,
+	features = "core"
+}
+```
+
+The `core` feature requires the `core` and `alloc` libraries and a nightly compiler.
+Also, code related to `std::error` is disabled.
+
+Floating point operations in `no_std` use [`libm`](https://crates.io/crates/libm), which sometimes panics in debug mode (https://github.com/japaric/libm/issues/4).
+So make sure to either use release builds or avoid WASM with floating point operations, for example by using [`deny_floating_point`](https://docs.rs/wasmi/0.4.0/wasmi/struct.Module.html#method.deny_floating_point).
+
 ## Contribution
 
 Unless you explicitly state otherwise, any contribution intentionally submitted

src/common/stack.rs

@@ -1,6 +1,9 @@
+#[allow(unused_imports)]
+use alloc::prelude::*;
 
+#[cfg(feature = "std")]
 use std::error;
-use std::fmt;
+use core::fmt;
 
 #[derive(Debug)]
 pub struct Error(String);
@@ -11,6 +14,7 @@ impl fmt::Display for Error {
 	}
 }
 
+#[cfg(feature = "std")]
 impl error::Error for Error {
 	fn description(&self) -> &str {
 		&self.0

src/func.rs

@@ -1,5 +1,7 @@
-use std::rc::{Rc, Weak};
-use std::fmt;
+#[allow(unused_imports)]
+use alloc::prelude::*;
+use alloc::rc::{Rc, Weak};
+use core::fmt;
 use parity_wasm::elements::Local;
 use {Trap, TrapKind, Signature};
 use host::Externals;
@@ -17,7 +19,7 @@ use isa;
 #[derive(Clone, Debug)]
 pub struct FuncRef(Rc<FuncInstance>);
 
-impl ::std::ops::Deref for FuncRef {
+impl ::core::ops::Deref for FuncRef {
 	type Target = FuncInstance;
 	fn deref(&self) -> &FuncInstance {
 		&self.0

src/global.rs

@@ -1,5 +1,5 @@
-use std::rc::Rc;
-use std::cell::Cell;
+use alloc::rc::Rc;
+use core::cell::Cell;
 use value::RuntimeValue;
 use Error;
 use types::ValueType;
@@ -13,7 +13,7 @@ use parity_wasm::elements::{ValueType as EValueType};
 #[derive(Clone, Debug)]
 pub struct GlobalRef(Rc<GlobalInstance>);
 
-impl ::std::ops::Deref for GlobalRef {
+impl ::core::ops::Deref for GlobalRef {
 	type Target = GlobalInstance;
 	fn deref(&self) -> &GlobalInstance {
 		&self.0

src/host.rs

@@ -1,4 +1,4 @@
-use std::any::TypeId;
+use core::any::TypeId;
 use value::{RuntimeValue, FromRuntimeValue};
 use {TrapKind, Trap};
 
@@ -98,7 +98,7 @@ impl<'a> RuntimeArgs<'a> {
 ///     _ => panic!(),
 /// }
 /// ```
-pub trait HostError: 'static + ::std::fmt::Display + ::std::fmt::Debug + Send + Sync {
+pub trait HostError: 'static + ::core::fmt::Display + ::core::fmt::Debug + Send + Sync {
 	#[doc(hidden)]
 	fn __private_get_type_id__(&self) -> TypeId {
 		TypeId::of::<Self>()

src/imports.rs

@@ -1,4 +1,11 @@
+#[allow(unused_imports)]
+use alloc::prelude::*;
+
+#[cfg(feature = "std")]
 use std::collections::HashMap;
+#[cfg(not(feature = "std"))]
+use hashmap_core::HashMap;
+
 use global::GlobalRef;
 use memory::MemoryRef;
 use func::FuncRef;

src/isa.rs

@@ -67,6 +67,9 @@
 //! - Reserved immediates are ignored for `call_indirect`, `current_memory`, `grow_memory`.
 //!
 
+#[allow(unused_imports)]
+use alloc::prelude::*;
+
 /// Should we keep a value before "discarding" a stack frame?
 ///
 /// Note that this is a `enum` since Wasm doesn't support multiple return

src/lib.rs

@@ -96,6 +96,21 @@
 
 #![warn(missing_docs)]
 
+#![cfg_attr(not(feature = "std"), no_std)]
+
+//// alloc is required in no_std
+#![cfg_attr(not(feature = "std"), feature(alloc))]
+
+#[cfg(not(feature = "std"))]
+#[macro_use]
+extern crate alloc;
+#[cfg(feature = "std")]
+extern crate std as alloc;
+
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate core;
+
 #[cfg(test)]
 extern crate wabt;
 #[cfg(test)]
@@ -104,13 +119,19 @@ extern crate assert_matches;
 
 extern crate parity_wasm;
 extern crate byteorder;
+#[cfg(not(feature = "std"))]
+extern crate hashmap_core;
 extern crate memory_units as memory_units_crate;
 
-pub extern crate nan_preserving_float;
-
-use std::fmt;
+#[allow(unused_imports)]
+use alloc::prelude::*;
+use core::fmt;
+#[cfg(feature = "std")]
 use std::error;
 
+#[cfg(not(feature = "std"))]
+extern crate libm;
+
 /// Error type which can be thrown by wasm code or by host environment.
 ///
 /// Under some conditions, wasm execution may produce a `Trap`, which immediately aborts execution.
@@ -138,6 +159,7 @@ impl fmt::Display for Trap {
 	}
 }
 
+#[cfg(feature = "std")]
 impl error::Error for Trap {
 	fn description(&self) -> &str {
 		"runtime trap"
@@ -308,6 +330,7 @@ impl fmt::Display for Error {
 	}
 }
 
+#[cfg(feature = "std")]
 impl error::Error for Error {
 	fn description(&self) -> &str {
 		match *self {
@@ -367,6 +390,7 @@ mod global;
 mod func;
 mod types;
 mod isa;
+pub mod nan_preserving_float;
 
 #[cfg(test)]
 mod tests;