Switch from Emscripten to clang+WASI SDK for building decoder

To make it easier to build gltfpack as a library, we're going to switch to clang and WASI SDK for building Wasm code in this codebase. This change starts the process by converting meshopt_decoder.js to this. Since WASI SDK doesn't provide a small enough memcpy/memset by default, or a version of sbrk() that actually works with byte aligned allocations, we provide our own versions for now to keep the size minimal. As a result, the cumulative size of .js.gz actually decreases by 337 bytes. To build the decoder, you now need to specify paths to clang-11 (unless clang is clang-11 on the target system) and WASI SDK: make WASMCC=clang-11 WASI_SDK=../wasi js/meshopt_decoder.js
zeux · Oct 8, 2020 · ff4308d · ff4308d
1 parent a507623
commit ff4308d
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Showing 4 changed files with 115 additions and 12 deletions.
diff --git a/Makefile b/Makefile
@@ -1,4 +1,5 @@
 MAKEFLAGS+=-r -j
+COMMA=,
 
 config=debug
 files=demo/pirate.obj
@@ -23,11 +24,15 @@ CFLAGS=-g -Wall -Wextra -Werror -std=c89
 CXXFLAGS=-g -Wall -Wextra -Wshadow -Wno-missing-field-initializers -Werror -std=c++98
 LDFLAGS=
 
-WASM_SOURCES=src/vertexcodec.cpp src/indexcodec.cpp src/vertexfilter.cpp
-WASM_EXPORTS="__initialize","_sbrk"
-WASM_EXPORTS+=,"_meshopt_decodeVertexBuffer","_meshopt_decodeIndexBuffer","_meshopt_decodeIndexSequence"
-WASM_EXPORTS+=,"_meshopt_decodeFilterOct","_meshopt_decodeFilterQuat","_meshopt_decodeFilterExp"
-WASM_FLAGS=-O3 -DNDEBUG -s EXPORTED_FUNCTIONS='[$(WASM_EXPORTS)]' -s ALLOW_MEMORY_GROWTH=1 -s TOTAL_STACK=24576 -s TOTAL_MEMORY=65536 --no-entry
+WASMCC=clang
+WASI_SDK=
+
+WASM_SOURCES=src/vertexcodec.cpp src/indexcodec.cpp src/vertexfilter.cpp tools/wasmstubs.cpp
+WASM_EXPORTS=meshopt_decodeVertexBuffer meshopt_decodeIndexBuffer meshopt_decodeIndexSequence meshopt_decodeFilterOct meshopt_decodeFilterQuat meshopt_decodeFilterExp sbrk __wasm_call_ctors
+WASM_FLAGS=--target=wasm32-wasi --sysroot=$(WASI_SDK)
+WASM_FLAGS+=$(patsubst %,-Wl$(COMMA)--export=%,$(WASM_EXPORTS))
+WASM_FLAGS+=-O3 -DNDEBUG -nostartfiles -nostdlib -Wl,--no-entry -Wl,-s
+WASM_FLAGS+=-Wl,-z -Wl,stack-size=24576 -Wl,--initial-memory=65536
 
 ifeq ($(config),iphone)
 	IPHONESDK=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk
@@ -88,14 +93,14 @@ gltf/bin/gltfpack.js: ${LIBRARY_SOURCES} ${GLTFPACK_SOURCES} tools/meshloader.cp
 
 build/decoder_base.wasm: $(WASM_SOURCES)
 	@mkdir -p build
-	emcc $^ $(WASM_FLAGS) -o $@
+	$(WASMCC) $^ $(WASM_FLAGS) -o $@
 
 build/decoder_simd.wasm: $(WASM_SOURCES)
 	@mkdir -p build
-	emcc $^ $(WASM_FLAGS) -o $@ -msimd128 -mbulk-memory
+	$(WASMCC) $^ $(WASM_FLAGS) -o $@ -msimd128 -mbulk-memory
 
 js/meshopt_decoder.js: build/decoder_base.wasm build/decoder_simd.wasm
-	sed -i "s#Built with emcc.*#Built with $$(emcc --version | head -n 1)#" $@
+	sed -i "s#Built with clang.*#Built with $$($(WASMCC) --version | head -n 1)#" $@
 	sed -i "s#\(var wasm_base = \)\".*\";#\\1\"$$(cat build/decoder_base.wasm | python3 tools/wasmpack.py)\";#" $@
 	sed -i "s#\(var wasm_simd = \)\".*\";#\\1\"$$(cat build/decoder_simd.wasm | python3 tools/wasmpack.py)\";#" $@