Add makefile to wasm recipe in the book

src/SUMMARY.md

@@ -6,4 +6,6 @@
   - [Retrofitting sandboxing in a simple application](./chapters/noop-sandbox.md)
   - [Enforcing isolation with the `wasm2c` sandbox](./chapters/wasm-sandbox.md)
   - [Installing and running tutorial examples](./chapters/tutorial-install.md)
-- [Additional material](chapters/appendix.md)
+- [Additional resources](./chapters/additional.md)
+  - [Modifying a project that uses Make to compile to Wasm](./chapters/makefile-wasm.md)
+  - [More tutorials](chapters/appendix.md)

src/additional.md

@@ -0,0 +1,4 @@
+# Additional content
+
+This section contains additional resources such as useful recipes, tutorials
+which may have additional content (but may be slightly out of date) etc.

src/chapters/makefile-wasm.md

@@ -0,0 +1,26 @@
+# Modifying a Makefile based project to compile to Wasm
+
+This tutorial assumes you have the
+[rlbox_wasm2c_sandbox](https://github.com/PLSysSec/rlbox_wasm2c_sandbox/) git
+repo is in the path $(RLBOX_WASM2C_PATH), and you have installed
+[wasi-sdk](https://github.com/WebAssembly/wasi-sdk/releases) on your computer in
+the path $(WASI_SDK_PATH)
+
+Build the sources of your library along with the file
+`$(RLBOX_WASM2C_PATH)/c_src/wasm2c_sandbox_wrapper.c`. Pass the flags `-Wl,--export-all -Wl,--stack-first -Wl,-z,stack-size=262144 -Wl,--no-entry -Wl,--growable-table -Wl,--import-memory -Wl,--import-table`
+to the linker using the wasi-clang compiler. This will produce a wasm module.
+
+To edit an existing Make based build system, you can run the commmand.
+
+```bash
+$(WASI_SDK_PATH)/bin/clang --sysroot $(WASI_SDK_PATH)/share/wasi-sysroot $(RLBOX_WASM2C_PATH)/c_src/wasm2c_sandbox_wrapper.c -c -o $(RLBOX_WASM2C_PATH)/c_src/wasm2c_sandbox_wrapper.o
+
+AR=$(WASI_SDK_PATH)/bin/ar                                  \
+CC=$(WASI_SDK_PATH)/bin/clang                               \
+CXX=$(WASI_SDK_PATH)/bin/clang++                            \
+CFLAGS="--sysroot $(WASI_SDK_PATH)/share/wasi-sysroot"      \
+LD=$(WASI_SDK_PATH)/bin/wasm-ld                             \
+LDLIBS=$(RLBOX_WASM2C_PATH)/c_src/wasm2c_sandbox_wrapper.o  \
+LDFLAGS="-Wl,--export-all -Wl,--stack-first -Wl,-z,stack-size=262144 -Wl,--no-entry -Wl,--growable-table -Wl,--import-memory -Wl,--import-table"   \
+make
+```