Fixed commands for makefile update

Author: shravanrn

src/chapters/additional/makefile-wasm.md

@@ -2,25 +2,47 @@
 
 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
+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)
+the path $WASI_SDK_PATH
 
 Build the sources of your library along with the file
-`$(RLBOX_WASM2C_PATH)/c_src/wasm2c_sandbox_wrapper.c`. Pass the flags `-Wl,--export-all -Wl,--stack-first -Wl,-z,stack-size=262144 -Wl,--no-entry -Wl,--growable-table -Wl,--import-memory -Wl,--import-table`
+`$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=$(RLBOX_WASM2C_PATH)/c_src/wasm2c_sandbox_wrapper.o  \
+$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=$RLBOX_WASM2C_PATH/c_src/wasm2c_sandbox_wrapper.o  \
 LDFLAGS="-Wl,--export-all -Wl,--stack-first -Wl,-z,stack-size=262144 -Wl,--no-entry -Wl,--growable-table -Wl,--import-memory -Wl,--import-table"   \
 make
 ```
+
+If the Makefile you are modifying produces a binary executable, this will change it produce a Wasm executable instead and that should be it.
+
+If the Makefile produces a static library (e.g., `mylib.a`) instead. You need
+one additional step to make it usable as a Wasm library that can be imported by
+rlbox.
+
+First create a dummy main file somewhere called `dummy-main.c` consisting of
+
+```c
+int main(int argc, char**argv){
+    return 0;
+}
+```
+
+Then you can run the following command
+
+```bash
+$WASI_SDK_PATH/bin/clang --sysroot $WASI_SDK_PATH/share/wasi-sysroot -o mylib.wasm dummy-main.c -Wl,--whole-archive mylib.a -Wl,--no-whole-archive -Wl,--export-all
+```
+
+This compiles a Wasm file with all symbols from the library included and exported.