add wasm32-wasi-preview2 target

Currently, this is identical to the `wasm32-wasi` in all but name.  See WebAssembly#449 for
the next step, which is to incrementally add Preview 2 features,
e.g. `wasi-sockets`.  Per the discussion in that PR, I've split the
`wasi-sysroot/include` directory into per-target directories.  Eventually, we'll
want to build a separate sysroot for each target, but there's currently
uncertainty about how to configure the default sysroot for e.g. clang, so we're
not tackling that yet.

See also WebAssembly#447 for further details.

Signed-off-by: Joel Dice <[email protected]>

.github/workflows/main.yml

@@ -84,7 +84,9 @@ jobs:
 
     - name: Build libc
       shell: bash
-      run: make -j4
+      run: |
+        make -j4
+        WASI_SNAPSHOT=preview2 make -j4
 
     - name: Test
       shell: bash
@@ -98,6 +100,8 @@ jobs:
         mkdir -p $WASI_DIR
         cp download/lib/wasi/libclang_rt.builtins-wasm32.a $WASI_DIR
         make test
+        rm -r build
+        WASI_SNAPSHOT=preview2 make test
       # The older version of Clang does not provide the expected symbol for the
       # test entrypoints: `undefined symbol: __main_argc_argv`.
       # The older (<15.0.7) version of wasm-ld does not provide `__heap_end`,

Makefile

@@ -15,6 +15,8 @@ SYSROOT ?= $(CURDIR)/sysroot
 INSTALL_DIR ?= /usr/local
 # single or posix; note that pthread support is still a work-in-progress.
 THREAD_MODEL ?= single
+# preview1 or preview2; the latter is not (yet) compatible with multithreading
+WASI_SNAPSHOT ?= preview1
 # dlmalloc or none
 MALLOC_IMPL ?= dlmalloc
 # yes or no
@@ -41,6 +43,10 @@ ifeq ($(THREAD_MODEL), posix)
 TARGET_TRIPLE = wasm32-wasi-threads
 endif
 
+ifeq ($(WASI_SNAPSHOT), preview2)
+TARGET_TRIPLE = wasm32-wasi-preview2
+endif
+
 BUILTINS_LIB ?= $(shell ${CC} --print-libgcc-file-name)
 
 # These variables describe the locations of various files and directories in
@@ -386,7 +392,7 @@ LIBC_BOTTOM_HALF_CRT_OBJS = $(call objs,$(LIBC_BOTTOM_HALF_CRT_SOURCES))
 # These variables describe the locations of various files and
 # directories in the generated sysroot tree.
 SYSROOT_LIB := $(SYSROOT)/lib/$(TARGET_TRIPLE)
-SYSROOT_INC = $(SYSROOT)/include
+SYSROOT_INC = $(SYSROOT)/include/$(TARGET_TRIPLE)
 SYSROOT_SHARE = $(SYSROOT)/share/$(TARGET_TRIPLE)
 
 # Files from musl's include directory that we don't want to install in the
@@ -511,7 +517,7 @@ PIC_OBJS = \
 # to CC.  This is a workaround for a Windows command line size limitation.  See
 # the `%.a` rule below for details.
 $(SYSROOT_LIB)/%.so: $(OBJDIR)/%.so.a $(BUILTINS_LIB)
-	$(CC) -nodefaultlibs -shared --sysroot=$(SYSROOT) \
+	$(CC) --target=$(TARGET_TRIPLE) -nodefaultlibs -shared --sysroot=$(SYSROOT) \
 	-o $@ -Wl,--whole-archive $< -Wl,--no-whole-archive $(BUILTINS_LIB)
 
 $(OBJDIR)/libc.so.a: $(LIBC_SO_OBJS) $(MUSL_PRINTSCAN_LONG_DOUBLE_SO_OBJS)