diff --git a/.circleci/config.yml b/.circleci/config.yml
index 8b3915d0..fcb30b20 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -49,6 +49,18 @@ commands:
           key: llvm-source-9-v0
           paths:
             - llvm-project
+  build-wasi-libc:
+    steps:
+      - restore_cache:
+          keys:
+            - wasi-libc-sysroot-v0
+      - run:
+          name: "Build wasi-libc"
+          command: make wasi-libc CLANG=$PWD/llvm-build/bin/clang LLVM_AR=$PWD/llvm-build/bin/llvm-ar LLVM_NM=$PWD/llvm-build/bin/llvm-nm
+      - save_cache:
+          key: wasi-libc-sysroot-v0
+          paths:
+            - lib/wasi-libc/sysroot
   test-linux:
     steps:
       - checkout
@@ -62,6 +74,14 @@ commands:
             - go-cache-v2-{{ checksum "go.mod" }}
       - llvm-source-linux
       - run: go install .
+      - restore_cache:
+          keys:
+            - wasi-libc-sysroot-systemclang-v0
+      - run: make wasi-libc
+      - save_cache:
+          key: wasi-libc-sysroot-systemclang-v0
+          paths:
+            - lib/wasi-libc/sysroot
       - run: go test -v ./cgo ./compileopts ./interp ./transform .
       - run: make gen-device -j4
       - run: make smoketest
@@ -119,6 +139,7 @@ commands:
           paths:
             llvm-build
       - run: make ASSERT=1
+      - build-wasi-libc
       - run:
           name: "Test TinyGo"
           command: make ASSERT=1 test
@@ -176,6 +197,7 @@ commands:
           key: llvm-build-9-linux-v0
           paths:
             llvm-build
+      - build-wasi-libc
       - run:
           name: "Test TinyGo"
           command: make test
@@ -242,6 +264,16 @@ commands:
           key: llvm-build-9-macos-v0
           paths:
             llvm-build
+      - restore_cache:
+          keys:
+            - wasi-libc-sysroot-macos-v0
+      - run:
+          name: "Build wasi-libc"
+          command: make wasi-libc CLANG=$PWD/llvm-build/bin/clang LLVM_AR=$PWD/llvm-build/bin/llvm-ar LLVM_NM=$PWD/llvm-build/bin/llvm-nm
+      - save_cache:
+          key: wasi-libc-sysroot-macos-v0
+          paths:
+            - lib/wasi-libc/sysroot
       - run:
           name: "Test TinyGo"
           command: make test
diff --git a/.gitmodules b/.gitmodules
index 36288c43..4d539c85 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -14,3 +14,6 @@
 	path = lib/compiler-rt
 	url = https://github.com/llvm-mirror/compiler-rt.git
 	branch = release_80
+[submodule "lib/wasi-libc"]
+	path = lib/wasi-libc
+	url = https://github.com/CraneStation/wasi-libc
diff --git a/Makefile b/Makefile
index ecc6d22f..2d4f2580 100644
--- a/Makefile
+++ b/Makefile
@@ -7,6 +7,11 @@ LLVM_BUILDDIR ?= llvm-build
 CLANG_SRC ?= llvm-project/clang
 LLD_SRC ?= llvm-project/lld
 
+# Default tool selection.
+CLANG ?= clang-9
+LLVM_AR ?= llvm-ar-9
+LLVM_NM ?= llvm-nm-9
+
 # Go binary and GOROOT to select
 GO ?= go
 export GOROOT = $(shell $(GO) env GOROOT)
@@ -139,12 +144,19 @@ $(LLVM_BUILDDIR): $(LLVM_BUILDDIR)/build.ninja
 	cd $(LLVM_BUILDDIR); ninja
 
 
+# Build wasi-libc sysroot
+.PHONY: wasi-libc
+wasi-libc: lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a
+lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a:
+	cd lib/wasi-libc && make -j4 WASM_CC=$(CLANG) WASM_AR=$(LLVM_AR) WASM_NM=$(LLVM_NM)
+
+
 # Build the Go compiler.
 tinygo:
 	@if [ ! -f "$(LLVM_BUILDDIR)/bin/llvm-config" ]; then echo "Fetch and build LLVM first by running:"; echo "  make llvm-source"; echo "  make $(LLVM_BUILDDIR)"; exit 1; fi
 	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) build -o build/tinygo$(EXE) -tags byollvm .
 
-test:
+test: wasi-libc
 	CGO_CPPFLAGS="$(CGO_CPPFLAGS)" CGO_CXXFLAGS="$(CGO_CXXFLAGS)" CGO_LDFLAGS="$(CGO_LDFLAGS)" $(GO) test -v -tags byollvm ./cgo ./compileopts ./interp ./transform .
 
 tinygo-test:
@@ -261,12 +273,13 @@ endif
 	$(TINYGO) build             -o wasm.wasm -target=wasm               examples/wasm/export
 	$(TINYGO) build             -o wasm.wasm -target=wasm               examples/wasm/main
 
-release: tinygo gen-device
+release: tinygo gen-device wasi-libc
 	@mkdir -p build/release/tinygo/bin
 	@mkdir -p build/release/tinygo/lib/clang/include
 	@mkdir -p build/release/tinygo/lib/CMSIS/CMSIS
 	@mkdir -p build/release/tinygo/lib/compiler-rt/lib
 	@mkdir -p build/release/tinygo/lib/nrfx
+	@mkdir -p build/release/tinygo/lib/wasi-libc
 	@mkdir -p build/release/tinygo/pkg/armv6m-none-eabi
 	@mkdir -p build/release/tinygo/pkg/armv7m-none-eabi
 	@mkdir -p build/release/tinygo/pkg/armv7em-none-eabi
@@ -279,6 +292,7 @@ release: tinygo gen-device
 	@cp -rp lib/compiler-rt/LICENSE.TXT  build/release/tinygo/lib/compiler-rt
 	@cp -rp lib/compiler-rt/README.txt   build/release/tinygo/lib/compiler-rt
 	@cp -rp lib/nrfx/*                   build/release/tinygo/lib/nrfx
+	@cp -rp lib/wasi-libc/sysroot        build/release/tinygo/lib/wasi-libc/sysroot
 	@cp -rp src                          build/release/tinygo/src
 	@cp -rp targets                      build/release/tinygo/targets
 	./build/tinygo build-builtins -target=armv6m-none-eabi  -o build/release/tinygo/pkg/armv6m-none-eabi/compiler-rt.a
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 5b6a5c04..ba5ff50e 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -45,6 +45,16 @@ jobs:
       inputs:
         targetType: inline
         script: choco install qemu
+    - task: CacheBeta@0
+      displayName: Cache wasi-libc sysroot
+      inputs:
+        key: wasi-libc-sysroot-v0
+        path: lib/wasi-libc/sysroot
+    - task: Bash@3
+      displayName: Build wasi-libc
+      inputs:
+        targetType: inline
+        script: make wasi-libc CLANG=$PWD/llvm-build/bin/clang LLVM_AR=$PWD/llvm-build/bin/llvm-ar LLVM_NM=$PWD/llvm-build/bin/llvm-nm
     - task: Bash@3
       displayName: Test TinyGo
       inputs:
diff --git a/lib/wasi-libc b/lib/wasi-libc
new file mode 160000
index 00000000..a280fead
--- /dev/null
+++ b/lib/wasi-libc
@@ -0,0 +1 @@
+Subproject commit a280fead2ae71b9a230d3b48c1f95867431888e4
diff --git a/src/runtime/runtime_wasm.go b/src/runtime/runtime_wasm.go
index 4264ea19..154739b8 100644
--- a/src/runtime/runtime_wasm.go
+++ b/src/runtime/runtime_wasm.go
@@ -2,10 +2,6 @@
 
 package runtime
 
-import (
-	"unsafe"
-)
-
 type timeUnit float64 // time in milliseconds, just like Date.now() in JavaScript
 
 const tickMicros = 1000000
@@ -68,25 +64,3 @@ func ticks() timeUnit
 func abort() {
 	trap()
 }
-
-//go:export memset
-func memset(ptr unsafe.Pointer, c byte, size uintptr) unsafe.Pointer {
-	for i := uintptr(0); i < size; i++ {
-		*(*byte)(unsafe.Pointer(uintptr(ptr) + i)) = c
-	}
-	return ptr
-}
-
-// Implement memmove for LLVM and compiler-rt.
-//go:export memmove
-func libc_memmove(dst, src unsafe.Pointer, size uintptr) unsafe.Pointer {
-	memmove(dst, src, size)
-	return dst
-}
-
-// Implement memcpy for LLVM and compiler-rt.
-//go:export memcpy
-func libc_memcpy(dst, src unsafe.Pointer, size uintptr) unsafe.Pointer {
-	memcpy(dst, src, size)
-	return dst
-}
diff --git a/targets/wasm.json b/targets/wasm.json
index e8cdb5e1..47c20825 100644
--- a/targets/wasm.json
+++ b/targets/wasm.json
@@ -1,21 +1,21 @@
 {
-	"llvm-target":   "wasm32-unknown-unknown-wasm",
+	"llvm-target":   "wasm32--wasi",
 	"build-tags":    ["js", "wasm"],
 	"goos":          "js",
 	"goarch":        "wasm",
 	"compiler":      "clang",
 	"linker":        "wasm-ld",
 	"cflags": [
-		"--target=wasm32",
-		"-nostdlibinc",
-		"-Wno-macro-redefined",
+		"--target=wasm32--wasi",
+		"--sysroot={root}/lib/wasi-libc/sysroot",
 		"-Oz"
 	],
 	"ldflags": [
 		"--allow-undefined",
 		"--no-threads",
 		"--stack-first",
-		"--export-all"
+		"--export-all",
+		"{root}/lib/wasi-libc/sysroot/lib/wasm32-wasi/libc.a"
 	],
 	"emulator":      ["node", "targets/wasm_exec.js"]
 }