ICU-22838 Add WebAssembly/WASI cross-compilation support

* Add config/mh-wasi and update configure script.

  WebAssembly/WASI does not support threads and dynamic linking, so
  the new mh-wasi file disables those features in ICU.

* Teach putilimp.h not to define U_TZSET, U_TIMEZONE, and U_TZNAME for WASI

  WASI does not define timezone-related functionalities, and wasi-libc
  does not provide tzset, timezone, and tzname. This change teaches
  putilimp.h not to define U_TZSET, U_TIMEZONE, and U_TZNAME for WASI.

* Add GitHub Actions workflow to cross-compile ICU4C for WebAssembly/WASI

Author: kateinoigakukun

.github/workflows/icu4c.yml

@@ -532,6 +532,50 @@ jobs:
         set PATH=C:\tools\msys64\mingw64\bin;%PATH%
         .\icuinfo.exe
 
+  # WebAssembly build using the WASI SDK.
+  wasm-wasi-sdk:
+    runs-on: ubuntu-22.04  # Updated in BRS
+    steps:
+      - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+
+      - name: Install WASI SDK
+        env:
+          WASI_SDK_DOWNLOAD_URL: https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-27/wasi-sdk-27.0-x86_64-linux.deb
+          WASI_SDK_DOWNLOAD_SHA256: 3ed68fc89e3299c0e2333360efac89ec60fbc01870732a486ab386267355cc80
+        run: |
+          wget -O /tmp/wasi-sdk.deb "${WASI_SDK_DOWNLOAD_URL}"
+          echo "${WASI_SDK_DOWNLOAD_SHA256}  /tmp/wasi-sdk.deb" | sha256sum -c -
+          sudo apt-get install /tmp/wasi-sdk.deb
+          echo "WASI_SDK_PATH=/opt/wasi-sdk" >> $GITHUB_ENV
+
+      - name: Build tools for host system
+        run: |
+          TOOLS_BUILD_DIR="$PWD/build/tools";
+          mkdir -p "$TOOLS_BUILD_DIR";
+          pushd "$TOOLS_BUILD_DIR";
+          ../../icu4c/source/configure
+          make -j$(nproc)
+          echo "TOOLS_BUILD_DIR=$TOOLS_BUILD_DIR" >> $GITHUB_ENV
+
+      - name: Cross-build for WebAssembly with WASI SDK
+        run: |
+          CROSS_BUILD_DIR="$PWD/build/cross";
+          mkdir -p "$CROSS_BUILD_DIR";
+          pushd "$CROSS_BUILD_DIR";
+          ../../icu4c/source/configure --host=wasm32-unknown-wasip1 \
+            --with-cross-build="$TOOLS_BUILD_DIR" \
+            --enable-static --disable-shared \
+            --disable-tools --disable-tests \
+            --disable-samples --disable-extras \
+            --with-data-packaging=static \
+            --prefix / \
+            CC="$WASI_SDK_PATH/bin/clang" CXX="$WASI_SDK_PATH/bin/clang++" \
+            AR="$WASI_SDK_PATH/bin/llvm-ar" RANLIB="$WASI_SDK_PATH/bin/llvm-ranlib" \
+            CFLAGS="-D_WASI_EMULATED_SIGNAL" \
+            CXXFLAGS="-fno-exceptions -D_WASI_EMULATED_SIGNAL"
+          make -j$(nproc) PKGDATA_OPTS="--without-assembly -O $CROSS_BUILD_DIR/data/icupkg.inc"
+          make install DESTDIR="$CROSS_BUILD_DIR/install"
+
   # Run ICU4C tests with stubdata.
   run-with-stubdata:
     runs-on: ubuntu-22.04  # Updated in BRS

icu4c/source/acinclude.m4

@@ -85,6 +85,7 @@ powerpc*-apple-darwin*)	icu_cv_host_frag=mh-darwin-ppc ;;
 *-dec-osf*) icu_cv_host_frag=mh-alpha-osf ;;
 *-*-nto*)	icu_cv_host_frag=mh-qnx ;;
 *-ncr-*)	icu_cv_host_frag=mh-mpras ;;
+*-wasi*)	icu_cv_host_frag=mh-wasi ;;
 *) 		icu_cv_host_frag=mh-unknown ;;
 esac
 		]

icu4c/source/common/putilimp.h

@@ -107,6 +107,8 @@ typedef size_t uintptr_t;
    /* not defined */
 #elif U_PLATFORM == U_PF_HAIKU
    /* not defined */
+#elif defined(__wasi__)
+   /* not defined */
 #else
 #   define U_TZSET tzset
 #endif
@@ -132,6 +134,8 @@ typedef size_t uintptr_t;
    /* not defined */
 #elif U_PLATFORM == U_PF_IPHONE
    /* not defined */
+#elif defined(__wasi__)
+   /* not defined */
 #else
 #   define U_TIMEZONE timezone
 #endif
@@ -147,6 +151,8 @@ typedef size_t uintptr_t;
    /* not defined */
 #elif U_PLATFORM == U_PF_HAIKU
     /* not defined, (well it is but a loop back to icu) */
+#elif defined(__wasi__)
+   /* not defined */
 #else
 #   define U_TZNAME tzname
 #endif

icu4c/source/config/mh-wasi

@@ -0,0 +1,76 @@
+## -*-makefile-*-
+## Copyright (C) 2024 and later: Unicode, Inc. and others.
+## License & terms of use: http://www.unicode.org/copyright.html
+## WASI-specific setup
+
+## Commands to generate dependency files
+GEN_DEPS.c=  $(CC) -E -MM $(DEFS) $(CPPFLAGS)
+GEN_DEPS.cc= $(CXX) -E -MM $(DEFS) $(CPPFLAGS) $(CXXFLAGS)
+
+## Flags for position independent code
+SHAREDLIBCFLAGS = -fPIC
+SHAREDLIBCXXFLAGS = -fPIC
+SHAREDLIBCPPFLAGS = -DPIC
+
+## Additional flags when building libraries and with threads
+# WASI Preview 1 without wasi-threads does not support threads
+THREADSCPPFLAGS =
+LIBCPPFLAGS =
+
+## Compiler switch to embed a runtime search path
+LD_RPATH=
+LD_RPATH_PRE =
+
+## These are the library specific LDFLAGS
+LDFLAGSICUDT=-nodefaultlibs -nostdlib
+
+## Shared object suffix
+SO = so
+## Non-shared intermediate object suffix
+STATIC_O = ao
+
+## Compilation rules
+%.$(STATIC_O): $(srcdir)/%.c
+	$(call SILENT_COMPILE,$(strip $(COMPILE.c) $(STATICCPPFLAGS) $(STATICCFLAGS)) -o $@ $<)
+%.o: $(srcdir)/%.c
+	$(call SILENT_COMPILE,$(strip $(COMPILE.c) $(DYNAMICCPPFLAGS) $(DYNAMICCFLAGS)) -o $@ $<)
+
+%.$(STATIC_O): $(srcdir)/%.cpp
+	$(call SILENT_COMPILE,$(strip $(COMPILE.cc) $(STATICCPPFLAGS) $(STATICCXXFLAGS)) -o $@ $<)
+%.o: $(srcdir)/%.cpp
+	$(call SILENT_COMPILE,$(strip $(COMPILE.cc) $(DYNAMICCPPFLAGS) $(DYNAMICCXXFLAGS)) -o $@ $<)
+
+
+## Dependency rules
+%.d: $(srcdir)/%.c
+	$(call ICU_MSG,(deps)) $<
+	@$(SHELL) -ec '$(GEN_DEPS.c) $< \
+		| sed '\''s%\($*\)\.o[ :]*%\1.o $@ : %g'\'' > $@; \
+		[ -s $@ ] || rm -f $@'
+
+%.d: $(srcdir)/%.cpp
+	$(call ICU_MSG,(deps)) $<
+	@$(SHELL) -ec '$(GEN_DEPS.cc) $< \
+		| sed '\''s%\($*\)\.o[ :]*%\1.o $@ : %g'\'' > $@; \
+		[ -s $@ ] || rm -f $@'
+
+## Versioned libraries rules
+
+%.$(SO).$(SO_TARGET_VERSION_MAJOR): %.$(SO).$(SO_TARGET_VERSION)
+	$(RM) $@ && ln -s ${<F} $@
+%.$(SO): %.$(SO).$(SO_TARGET_VERSION_MAJOR)
+	$(RM) $@ && ln -s ${*F}.$(SO).$(SO_TARGET_VERSION) $@
+
+##  Bind internal references
+
+# LDflags that pkgdata will use
+BIR_LDFLAGS= -Wl,-Bsymbolic
+
+# Dependencies [i.e. map files] for the final library
+BIR_DEPS=
+
+## Remove shared library 's'
+STATIC_PREFIX_WHEN_USED = 
+STATIC_PREFIX = 
+
+## End WASI-specific setup

icu4c/source/configure

@@ -5833,6 +5833,7 @@ powerpc*-apple-darwin*)	icu_cv_host_frag=mh-darwin-ppc ;;
 *-dec-osf*) icu_cv_host_frag=mh-alpha-osf ;;
 *-*-nto*)	icu_cv_host_frag=mh-qnx ;;
 *-ncr-*)	icu_cv_host_frag=mh-mpras ;;
+*-wasi*)	icu_cv_host_frag=mh-wasi ;;
 *) 		icu_cv_host_frag=mh-unknown ;;
 esac