[wasm] Add metadata registration for WebAssembly

This patch adds the metadata registration for the wasm targets, and also
adds build support for it.

Author: kateinoigakukun

stdlib/public/runtime/CMakeLists.txt

@@ -87,7 +87,7 @@ set(swift_runtime_backtracing_sources
 # Acknowledge that the following sources are known.
 set(LLVM_OPTIONAL_SOURCES
     SwiftRT-COFF.cpp
-    SwiftRT-ELF.cpp
+    SwiftRT-ELF-WASM.cpp
     ${swift_runtime_sources}
     ${swift_runtime_objc_sources}
     ${swift_runtime_leaks_sources}
@@ -138,11 +138,14 @@ add_swift_target_library(swiftRuntime OBJECT_LIBRARY
 
 set(ELFISH_SDKS)
 set(COFF_SDKS)
+set(WASM_SDKS)
 foreach(sdk ${SWIFT_SDKS})
   if("${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "ELF")
     list(APPEND ELFISH_SDKS ${sdk})
   elseif("${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "COFF")
     list(APPEND COFF_SDKS ${sdk})
+  elseif("${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "WASM")
+    list(APPEND WASM_SDKS ${sdk})
   endif()
 endforeach()
 
@@ -151,7 +154,7 @@ endforeach()
 # with LTO, force swift runtime to compile without LTO for Linux.
 add_swift_target_library(swiftImageRegistrationObjectELF
                   OBJECT_LIBRARY IS_STDLIB IS_STDLIB_CORE
-                  SwiftRT-ELF.cpp
+                  SwiftRT-ELF-WASM.cpp
                   C_COMPILE_FLAGS ${SWIFT_RUNTIME_CORE_CXX_FLAGS}
                   C_COMPILE_FLAGS_LINUX -fno-lto
                   LINK_FLAGS ${SWIFT_RUNTIME_CORE_LINK_FLAGS}
@@ -169,17 +172,32 @@ add_swift_target_library(swiftImageRegistrationObjectCOFF
                   SWIFT_COMPILE_FLAGS ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
                   INSTALL_IN_COMPONENT none)
 
+add_swift_target_library(swiftImageRegistrationObjectWASM
+                  OBJECT_LIBRARY IS_STDLIB IS_STDLIB_CORE
+                  SwiftRT-ELF-WASM.cpp
+                  C_COMPILE_FLAGS ${SWIFT_RUNTIME_CORE_CXX_FLAGS}
+                  LINK_FLAGS ${SWIFT_RUNTIME_CORE_LINK_FLAGS}
+                  TARGET_SDKS ${WASM_SDKS}
+                  SWIFT_COMPILE_FLAGS ${SWIFT_STANDARD_LIBRARY_SWIFT_FLAGS}
+                  INSTALL_IN_COMPONENT none)
+
 foreach(sdk ${SWIFT_SDKS})
   foreach(arch ${SWIFT_SDK_${sdk}_ARCHITECTURES})
     set(arch_subdir "${SWIFT_SDK_${sdk}_LIB_SUBDIR}/${arch}")
     set(arch_suffix "${SWIFT_SDK_${sdk}_LIB_SUBDIR}-${arch}")
 
     if("${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "ELF" OR
-       "${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "COFF")
+       "${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "COFF" OR
+       "${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "WASM")
       # TODO(compnerd) switch to the generator expression when cmake is upgraded
       # to a version which supports it.
       # set(swiftrtObject "$<TARGET_OBJECTS:swiftImageRegistrationObject${SWIFT_SDK_${sdk}_OBJECT_FORMAT}-${arch_suffix}>")
-      set(swiftrtObject ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/swiftImageRegistrationObject${SWIFT_SDK_${sdk}_OBJECT_FORMAT}-${arch_suffix}.dir/SwiftRT-${SWIFT_SDK_${sdk}_OBJECT_FORMAT}.cpp${CMAKE_C_OUTPUT_EXTENSION})
+      set(swiftrtSourceName SwiftRT-${SWIFT_SDK_${sdk}_OBJECT_FORMAT}.cpp)
+      if("${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "ELF" OR
+         "${SWIFT_SDK_${sdk}_OBJECT_FORMAT}" STREQUAL "WASM")
+       set(swiftrtSourceName SwiftRT-ELF-WASM.cpp)
+      endif()
+      set(swiftrtObject ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/swiftImageRegistrationObject${SWIFT_SDK_${sdk}_OBJECT_FORMAT}-${arch_suffix}.dir/${swiftrtSourceName}${CMAKE_C_OUTPUT_EXTENSION})
 
       if(sdk STREQUAL WINDOWS)
         set(extension .obj)

stdlib/public/runtime/SwiftRT-ELF.cpp renamed to stdlib/public/runtime/SwiftRT-ELF-WASM.cpp

@@ -1,4 +1,4 @@
-//===--- SwiftRT-ELF.cpp --------------------------------------------------===//
+//===--- SwiftRT-ELF-WASM.cpp ---------------------------------------------===//
 //
 // This source file is part of the Swift.org open source project
 //
@@ -16,14 +16,25 @@
 #include <cstddef>
 #include <new>
 
+#if defined(__ELF__)
 extern "C" const char __dso_handle[];
+#elif defined(__wasm__)
+// NOTE: Multi images in a single process is not yet
+// stabilized in WebAssembly toolchain outside of Emscripten.
+static constexpr const void *__dso_handle = nullptr;
+#endif
 
 // Create empty sections to ensure that the start/stop symbols are synthesized
 // by the linker.  Otherwise, we may end up with undefined symbol references as
 // the linker table section was never constructed.
+#if defined(__ELF__)
+# define DECLARE_EMPTY_METADATA_SECTION(name) __asm__("\t.section " #name ",\"a\"\n");
+#elif defined(__wasm__)
+# define DECLARE_EMPTY_METADATA_SECTION(name) __asm__("\t.section " #name ",\"\",@\n");
+#endif
 
 #define DECLARE_SWIFT_SECTION(name)                                                          \
-  __asm__("\t.section " #name ",\"a\"\n");                                                   \
+  DECLARE_EMPTY_METADATA_SECTION(name)                                                                \
   __attribute__((__visibility__("hidden"),__aligned__(1))) extern const char __start_##name; \
   __attribute__((__visibility__("hidden"),__aligned__(1))) extern const char __stop_##name;