Implement the GC in Rust

This implements the current garbage collector in Rust. No changes were
made to the GC design -- it's just ports the one implemented in code
generator to Rust.

The goals are:

- Evaluate Rust for Motoko's RTS implementation
- Make the collector easier to read, understand, modify, and extend.

Current status: the code is complete in the sense that there aren't any
missing features/passes etc., but it's has bugs. I'm not sure how to
debug Wasm yet. There are also lots of TODOs in the code, mostly for
documentation.

Submitting a PR to get early feedback.

Author: osa1

.gitignore

@@ -3,6 +3,7 @@
 _out
 _output
 _build
+target
 
 **/*~
 /result*

default.nix

@@ -26,6 +26,7 @@ let
     nixpkgs.clang_10 # for native/wasm building
     nixpkgs.lld_10 # for wasm building
     nixpkgs.rustc
+    nixpkgs.cargo
   ];
 
   rtsEnv = ''

rts/Makefile

@@ -1,3 +1,5 @@
+SHELL:=bash -O globstar
+
 CLANG ?= clang-10
 WASM_CLANG ?= clang-10
 WASM_LD ?= wasm-ld-10
@@ -138,7 +140,6 @@ vpath %.c $(MUSLSRC)/src/math $(MUSLSRC)/src/stdio $(MUSLSRC)/src/string $(MUSLS
 #
 
 RTSFILES=rts idl bigint float char buf utf8_valid closure-table text blob url
-RTS_RUST_FILES=to_hex_digit
 
 _build/wasm/%.o: %.c rts.h buf.h | _build/wasm
 	$(WASM_CLANG) $(CLANG_FLAGS) $(WASM_FLAGS) $(TOMMATH_FLAGS) -I$(TOMMATHSRC) $< --output $@
@@ -155,16 +156,22 @@ _build/native/tommath_%.o: %.c rts.h buf.h | _build/native
 _build/wasm/musl_%.o: %.c | _build/wasm
 	$(WASM_CLANG) $(CLANG_FLAGS) $(WASM_FLAGS) $(MUSL_FLAGS) $< --output $@
 
-_build/wasm/%_rs.o: %.rs | _build/wasm
-	rustc $< --target=wasm32-unknown-emscripten -O --crate-type=lib -Crelocation-model=pic --emit=obj -o $@
+.PHONY: _build/wasm/motoko_rts.o
+_build/wasm/motoko_rts.o: | _build/wasm
+	cd motoko-rts && \
+	  cargo rustc --target=wasm32-unknown-emscripten --release -v -- -Crelocation-model=pic --emit=obj
+	cp motoko-rts/target/wasm32-unknown-emscripten/release/deps/motoko_rts*.o $@
 
-_build/native/%_rs.o: %.rs | _build/native
-	rustc $< -O --crate-type=lib -Crelocation-model=pic --emit=obj -o $@
+.PHONY: _build/native/motoko_rts.o
+_build/native/motoko_rts.o: | _build/native
+	cd motoko-rts && \
+	  cargo rustc --release -v -- -Crelocation-model=pic --emit=obj
+	cp motoko-rts/target/release/deps/motoko_rts*.o $@
 
 RTS_WASM_O=$(RTSFILES:%=_build/wasm/%.o)
 RTS_NATIVE_O=$(RTSFILES:%=_build/native/%.o)
-RTS_RUST_WASM_O=$(RTS_RUST_FILES:%=_build/wasm/%_rs.o)
-RTS_RUST_NATIVE_O=$(RTS_RUST_FILES:%=_build/native/%_rs.o)
+RTS_RUST_WASM_O=_build/wasm/motoko_rts.o
+RTS_RUST_NATIVE_O=_build/native/motoko_rts.o
 
 #
 # The actual RTS, as we ship it with the compiler
@@ -187,4 +194,4 @@ test_leb128: test_leb128.c $(RTS_NATIVE_O) $(RTS_RUST_NATIVE_O) $(TOMMATH_NATIVE
 	$(CLANG) -o $@ $+
 
 clean:
-	rm -rf _build mo-rts.wasm test_rts test_leb128
+	rm -rf _build mo-rts.wasm test_rts test_leb128 motoko-rts/target

rts/motoko-rts/.vim/coc-settings.json

@@ -0,0 +1,3 @@
+{
+    "rust-analyzer.cargo.target": "wasm32-unknown-emscripten"
+}

rts/motoko-rts/Cargo.lock

@@ -0,0 +1,7 @@
+[package]
+name = "motoko-rts"
+version = "0.1.0"
+authors = ["Ömer Sinan Ağacan <omeragacan@gmail.com>"]
+edition = "2018"
+
+[dependencies]

rts/motoko-rts/Cargo.toml

@@ -0,0 +1,21 @@
+use crate::common::rts_trap_with;
+use crate::types::{skew, Array, SkewedPtr};
+
+/// Returns address of Nth payload field of an array
+#[no_mangle]
+pub unsafe extern "C" fn array_field_addr(array: SkewedPtr, idx: u32) -> SkewedPtr {
+    let array_ptr = array.unskew() as *const Array;
+
+    if idx >= (*array_ptr).len {
+        rts_trap_with("Array index out of bounds\0".as_ptr());
+    }
+
+    let payload_begin = array_ptr.offset(1) as *const u32;
+    skew(payload_begin.offset(idx as isize) as usize)
+}
+
+/// Index an array. Does not check bounds.
+pub unsafe fn array_idx_unchecked(array_ptr: *const Array, idx: u32) -> SkewedPtr {
+    let payload_begin = array_ptr.offset(1) as *const u32;
+    SkewedPtr(*payload_begin.offset(idx as isize) as usize)
+}

rts/motoko-rts/src/array.rs

@@ -0,0 +1,3 @@
+extern "C" {
+    pub fn rts_trap_with(msg: *const u8) -> !;
+}