Replace the usage of dlopen with llvm::sys::DynamicLibrary

This will be helpful in order to support environments where dlfcn.h is
not available, e.g. Windows + mingw.

Author: tuliom

lld/ELF/CMakeLists.txt

@@ -21,11 +21,6 @@ endif()
 set(GNULTO_INCLUDE_DIR "" CACHE PATH "Additional directory, where CMake should search for plugin-api.h")
 if(LLD_ENABLE_GNU_LTO)
   find_package(GNULTO REQUIRED)
-  include(CheckSymbolExists)
-  check_symbol_exists(dlopen "dlfcn.h" HAVE_DLOPEN)
-  if(NOT HAVE_DLOPEN)
-    message(FATAL_ERROR "Could not find the definition of dlopen(). Is dlfcn.h available?")
-  endif()
 endif()
 
 configure_file(

lld/ELF/LTO.cpp

@@ -427,8 +427,6 @@ void BitcodeCompiler::addObject(IRFile &f,
 }
 
 #if LLD_ENABLE_GNU_LTO
-#include <dlfcn.h>
-
 GccIRCompiler *GccIRCompiler::singleton = nullptr;
 
 GccIRCompiler *GccIRCompiler::getInstance() {
@@ -460,13 +458,14 @@ GccIRCompiler::~GccIRCompiler() {
 }
 
 void GccIRCompiler::loadPlugin() {
-  plugin = dlopen(ctx.arg.plugin.data(), RTLD_NOW);
-  if (plugin == NULL) {
-    error(dlerror());
+  std::string Error;
+  plugin = llvm::sys::DynamicLibrary::getPermanentLibrary(ctx.arg.plugin.data(), &Error);
+  if (!plugin.isValid()) {
+    error(Error);
     return;
   }
-  void *tmp = dlsym(plugin, "onload");
-  if (tmp == NULL) {
+  void *tmp = plugin.getAddressOfSymbol("onload");
+  if (!tmp) {
     error("Plugin does not provide onload()");
     return;
   }

lld/ELF/LTO.h

@@ -25,6 +25,7 @@
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/DynamicLibrary.h"
 #include <memory>
 #include <vector>
 
@@ -114,7 +115,7 @@ class GccIRCompiler : public IRCompiler {
 #endif
   ld_plugin_all_symbols_read_handler allSymbolsReadHandler;
   // Handle for the shared library created via dlopen().
-  void *plugin;
+  llvm::sys::DynamicLibrary plugin;
 
   void initializeTv();
 };