ELF: restructure image metadata registration

Restructure the ELF handling to be completely agnostic to the OS.
Rather than usng the loader to query the section information, use the
linker to construct linker tables and synthetic markers for the
beginning and of the table.  Save off the values of these pointers and
pass them along through the constructor to the runtime for registration.

This removes the need for the begin/end objects.  Remove the special
construction of the begin/end objects through the special assembly
constructs, preferring to do this in C with a bit of inline assembly to
ensure that the section is always allocated.

Remove the special handling for the various targets, the empty object
file can be linked on all the targets.

The new object file has no requirements on the ordering.  It needs to
simply be injected into the link.

Name the replacement file `swiftrt.o` mirroring `crt.o` from libc.  Merge
the constructor and the definition into a single object file.

This approach is generally more portable, overall simpler to implement,
and more robust.

Thanks to Orlando Bassotto for help analyzing some of the odd behaviours
when switching over.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -716,19 +716,6 @@ function(_add_swift_library_single target name)
     set(SWIFTLIB_SINGLE_API_NOTES "${module_name}")
   endif()
 
-  # On platforms that use ELF binaries we add markers for metadata sections in
-  # the shared libraries using these object files.  This wouldn't be necessary
-  # if the link was done by the swift binary: rdar://problem/19007002
-  if(SWIFTLIB_SINGLE_TARGET_LIBRARY AND
-     "${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_OBJECT_FORMAT}" STREQUAL "ELF")
-    if("${libkind}" STREQUAL "SHARED")
-      set(arch_subdir "${SWIFTLIB_DIR}/${SWIFTLIB_SINGLE_SUBDIR}")
-
-      set(SWIFT_SECTIONS_OBJECT_BEGIN "${arch_subdir}/swift_begin.o")
-      set(SWIFT_SECTIONS_OBJECT_END   "${arch_subdir}/swift_end.o")
-    endif()
-  endif()
-
   if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "WINDOWS")
     swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
     swift_windows_generate_sdk_vfs_overlay(SWIFTLIB_SINGLE_VFS_OVERLAY_FLAGS)
@@ -828,12 +815,15 @@ function(_add_swift_library_single target name)
   endif()
 
   add_library("${target}" ${libkind}
-      ${SWIFT_SECTIONS_OBJECT_BEGIN}
-      ${SWIFTLIB_SINGLE_SOURCES}
-      ${SWIFTLIB_SINGLE_EXTERNAL_SOURCES}
-      ${INCORPORATED_OBJECT_LIBRARIES_EXPRESSIONS}
-      ${SWIFTLIB_SINGLE_XCODE_WORKAROUND_SOURCES}
-      ${SWIFT_SECTIONS_OBJECT_END})
+              ${SWIFTLIB_SINGLE_SOURCES}
+              ${SWIFTLIB_SINGLE_EXTERNAL_SOURCES}
+              ${INCORPORATED_OBJECT_LIBRARIES_EXPRESSIONS}
+              ${SWIFTLIB_SINGLE_XCODE_WORKAROUND_SOURCES})
+  if("${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_OBJECT_FORMAT}" STREQUAL "ELF" AND SWIFTLIB_TARGET_LIBRARY)
+    if("${libkind}" STREQUAL "SHARED")
+      target_sources(${target} PRIVATE $<TARGET_OBJECTS:swiftImageRegistrationObject-${SWIFT_SDK_${sdk}_LIB_SUBDIR}-${SWIFTLIB_SINGLE_ARCHITECTURE}>)
+    endif()
+  endif()
   _set_target_prefix_and_suffix("${target}" "${libkind}" "${SWIFTLIB_SINGLE_SDK}")
 
   if(SWIFTLIB_SINGLE_TARGET_LIBRARY)
@@ -872,17 +862,6 @@ function(_add_swift_library_single target name)
     set_property(TARGET "${target}" PROPERTY NO_SONAME ON)
   endif()
 
-  # The section metadata objects are generated sources, and we need to tell CMake
-  # not to expect to find them prior to their generation.
-  if(SWIFTLIB_SINGLE_TARGET_LIBRARY AND
-     "${SWIFT_SDK_${SWIFTLIB_SINGLE_SDK}_OBJECT_FORMAT}" STREQUAL "ELF")
-    if("${libkind}" STREQUAL "SHARED")
-      set_source_files_properties(${SWIFT_SECTIONS_OBJECT_BEGIN} PROPERTIES GENERATED 1)
-      set_source_files_properties(${SWIFT_SECTIONS_OBJECT_END} PROPERTIES GENERATED 1)
-      add_dependencies("${target}" section_magic)
-    endif()
-  endif()
-
   llvm_update_compile_flags(${target})
 
   set_output_directory(${target}

lib/Driver/ToolChains.cpp

@@ -1530,26 +1530,6 @@ bool toolchains::GenericUnix::shouldProvideRPathToLinker() const {
   return true;
 }
 
-std::string toolchains::GenericUnix::getPreInputObjectPath(
-    StringRef RuntimeLibraryPath) const {
-  // On Linux and FreeBSD and Haiku (really, ELF binaries) we need to add objects
-  // to provide markers and size for the metadata sections.
-  SmallString<128> PreInputObjectPath = RuntimeLibraryPath;
-  llvm::sys::path::append(PreInputObjectPath,
-      swift::getMajorArchitectureName(getTriple()));
-  llvm::sys::path::append(PreInputObjectPath, "swift_begin.o");
-  return PreInputObjectPath.str();
-}
-
-std::string toolchains::GenericUnix::getPostInputObjectPath(
-    StringRef RuntimeLibraryPath) const {
-  SmallString<128> PostInputObjectPath = RuntimeLibraryPath;
-  llvm::sys::path::append(PostInputObjectPath,
-      swift::getMajorArchitectureName(getTriple()));
-  llvm::sys::path::append(PostInputObjectPath, "swift_end.o");
-  return PostInputObjectPath.str();
-}
-
 ToolChain::InvocationInfo
 toolchains::GenericUnix::constructInvocation(const LinkJobAction &job,
                                              const JobContext &context) const {
@@ -1627,22 +1607,10 @@ toolchains::GenericUnix::constructInvocation(const LinkJobAction &job,
   }
 
   SmallString<128> SharedRuntimeLibPath;
-  SmallString<128> StaticRuntimeLibPath;
-  // Path to swift_begin.o and swift_end.o.
-  SmallString<128> ObjectLibPath;
   getRuntimeLibraryPath(SharedRuntimeLibPath, context.Args, *this);
 
-  // -static-stdlib uses the static lib path for libswiftCore but
-  // the shared lib path for swift_begin.o and swift_end.o.
-  if (staticExecutable || staticStdlib) {
-    getRuntimeStaticLibraryPath(StaticRuntimeLibPath, context.Args, *this);
-  }
-
-  if (staticExecutable) {
-    ObjectLibPath = StaticRuntimeLibPath;
-  } else {
-    ObjectLibPath = SharedRuntimeLibPath;
-  }
+  SmallString<128> StaticRuntimeLibPath;
+  getRuntimeStaticLibraryPath(StaticRuntimeLibPath, context.Args, *this);
 
   // Add the runtime library link path, which is platform-specific and found
   // relative to the compiler.
@@ -1655,10 +1623,12 @@ toolchains::GenericUnix::constructInvocation(const LinkJobAction &job,
     Arguments.push_back(context.Args.MakeArgString(SharedRuntimeLibPath));
   }
 
-  auto PreInputObjectPath = getPreInputObjectPath(ObjectLibPath);
-  if (!PreInputObjectPath.empty()) {
-    Arguments.push_back(context.Args.MakeArgString(PreInputObjectPath));
-  }
+  SmallString<128> swiftrtPath = SharedRuntimeLibPath;
+  llvm::sys::path::append(swiftrtPath,
+                          swift::getMajorArchitectureName(getTriple()));
+  llvm::sys::path::append(swiftrtPath, "swiftrt.o");
+  Arguments.push_back(context.Args.MakeArgString(swiftrtPath));
+
   addPrimaryInputsOfType(Arguments, context.Inputs, types::TY_Object);
   addInputsOfType(Arguments, context.InputActions, types::TY_Object);
 
@@ -1753,13 +1723,6 @@ toolchains::GenericUnix::constructInvocation(const LinkJobAction &job,
   context.Args.AddAllArgs(Arguments, options::OPT_Xlinker);
   context.Args.AddAllArgs(Arguments, options::OPT_linker_option_Group);
 
-  // Just before the output option, allow GenericUnix toolchains to add
-  // additional inputs.
-  auto PostInputObjectPath = getPostInputObjectPath(ObjectLibPath);
-  if (!PostInputObjectPath.empty()) {
-    Arguments.push_back(context.Args.MakeArgString(PostInputObjectPath));
-  }
-
   // This should be the last option, for convenience in checking output.
   Arguments.push_back("-o");
   Arguments.push_back(context.Output.getPrimaryOutputFilename().c_str());
@@ -1792,14 +1755,3 @@ std::string toolchains::Cygwin::getTargetForLinker() const {
   return "";
 }
 
-std::string toolchains::Cygwin::getPreInputObjectPath(
-    StringRef RuntimeLibraryPath) const {
-  // Cygwin does not add "begin" and "end" objects.
-  return "";
-}
-
-std::string toolchains::Cygwin::getPostInputObjectPath(
-    StringRef RuntimeLibraryPath) const {
-  // Cygwin does not add "begin" and "end" objects.
-  return "";
-}

lib/Driver/ToolChains.h

@@ -66,30 +66,6 @@ class LLVM_LIBRARY_VISIBILITY GenericUnix : public ToolChain {
   /// default is to return true (and so specify an -rpath).
   virtual bool shouldProvideRPathToLinker() const;
 
-  /// Provides a path to an object that should be linked first. On platforms
-  /// that use ELF binaries, an object that provides markers and sizes for
-  /// metadata sections must be linked first. Platforms that do not need this
-  /// object may return an empty string; no additional objects are linked in
-  /// this case.
-  ///
-  /// \param RuntimeLibraryPath A path to the Swift resource directory, which
-  ///        on ARM architectures will contain metadata "begin" and "end"
-  ///        objects.
-  virtual std::string
-  getPreInputObjectPath(StringRef RuntimeLibraryPath) const;
-
-  /// Provides a path to an object that should be linked last. On platforms
-  /// that use ELF binaries, an object that provides markers and sizes for
-  /// metadata sections must be linked last. Platforms that do not need this
-  /// object may return an empty string; no additional objects are linked in
-  /// this case.
-  ///
-  /// \param RuntimeLibraryPath A path to the Swift resource directory, which
-  ///        on ARM architectures will contain metadata "begin" and "end"
-  ///        objects.
-  virtual std::string
-  getPostInputObjectPath(StringRef RuntimeLibraryPath) const;
-
   InvocationInfo constructInvocation(const LinkJobAction &job,
                                      const JobContext &context) const override;
 
@@ -117,11 +93,6 @@ class LLVM_LIBRARY_VISIBILITY Cygwin : public GenericUnix {
 
   std::string getTargetForLinker() const override;
 
-  std::string getPreInputObjectPath(
-    StringRef RuntimeLibraryPath) const override;
-
-  std::string getPostInputObjectPath(
-    StringRef RuntimeLibraryPath) const override;
 public:
   Cygwin(const Driver &D, const llvm::Triple &Triple) : GenericUnix(D, Triple) {}
   ~Cygwin() = default;

lib/IRGen/GenDecl.cpp

@@ -2329,7 +2329,7 @@ llvm::Constant *IRGenModule::emitProtocolConformances() {
     sectionName = "__TEXT, __swift2_proto, regular, no_dead_strip";
     break;
   case llvm::Triple::ELF:
-    sectionName = ".swift2_protocol_conformances";
+    sectionName = "swift2_protocol_conformances";
     break;
   case llvm::Triple::COFF:
     sectionName = ".sw2prtc";
@@ -2352,7 +2352,7 @@ llvm::Constant *IRGenModule::emitTypeMetadataRecords() {
     sectionName = "__TEXT, __swift2_types, regular, no_dead_strip";
     break;
   case llvm::Triple::ELF:
-    sectionName = ".swift2_type_metadata";
+    sectionName = "swift2_type_metadata";
     break;
   case llvm::Triple::COFF:
     sectionName = ".sw2tymd";

lib/IRGen/GenReflection.cpp

@@ -769,7 +769,7 @@ static std::string getReflectionSectionName(IRGenModule &IGM,
     OS << ".sw3" << FourCC;
     break;
   case llvm::Triple::ELF:
-    OS << ".swift3_" << LongName;
+    OS << "swift3_" << LongName;
     break;
   case llvm::Triple::MachO:
     assert(LongName.size() <= 7 &&

stdlib/public/core/CMakeLists.txt

@@ -249,7 +249,6 @@ add_swift_library(swiftCore ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_STDLIB IS_STD
   # and the generated directory as dependencies.
   FILE_DEPENDS
     copy_shim_headers "${SWIFTLIB_DIR}/shims"
-    section_magic
     ${GROUP_INFO_JSON_FILE}
   SWIFT_COMPILE_FLAGS ${swift_stdlib_compile_flags}
   LINK_FLAGS ${swift_core_link_flags}