[OpenMP][libomptarget] Allow overriding function that gets ELF symbol info

[kevinsala]

Summary

The OpenMP target's NextGen plugins retrieve symbol information in the ELF image
(i.e., address and size) through the ELF section and ELF symbol objects. However,
the images of CUDA programs compute the address differently from the images of
AMDGPU programs:

• Address for CUDA symbols: image begin + section's offset + symbol's st_value
• Address for AMDGPU symbols: image + begin + symbol's st_value

This patch prepares the PluginInterface for the new AMDGPU NextGen plugin.

[jdoerfert]

LG

openmp/libomptarget/plugins-nextgen/common/PluginInterface/GlobalHandler.h

class GenericGlobalHandlerTy {
   /// Map to store the ELF object files that have been loaded.
   llvm::DenseMap<int32_t, ELF64LEObjectFile> ELFObjectFiles;
 
   /// Get the cached ELF64LEObjectFile previosuly created for a specific
   /// device image or create it if did not exist.
   const ELF64LEObjectFile *
   getOrCreateELFObjectFile(const GenericDeviceTy &Device, DeviceImageTy &Image);
 
+  /// Extract the global's information from the ELF image, section, and symbol.
+  virtual Error getGlobalMetadataFromELF(const DeviceImageTy &Image,
+                                         const ELF64LE::Sym &Symbol,
+                                         const ELF64LE::Shdr &Section,
+                                         GlobalTy &ImageGlobal);
+
   /// Actually move memory between host and device. See readGlobalFromDevice and
   /// writeGlobalToDevice for the interface description.
   Error moveGlobalBetweenDeviceAndHost(GenericDeviceTy &Device,
                                        DeviceImageTy &Image,
                                        const GlobalTy &HostGlobal,
                                        bool Device2Host);
 
   /// Actually move memory between host and device. See readGlobalFromDevice and

openmp/libomptarget/plugins-nextgen/common/PluginInterface/GlobalHandler.cpp

GenericGlobalHandlerTy::getOrCreateELFObjectFile(const GenericDeviceTy &Device,
   auto Result =
       ELFObjectFiles.try_emplace(Image.getId(), std::move(ElfOrErr.get()));
   assert(Result.second && "Map insertion failed");
   assert(Result.first != ELFObjectFiles.end() && "Map insertion failed");
 
   return &Result.first->second;
 }
 
+Error GenericGlobalHandlerTy::getGlobalMetadataFromELF(
+    const DeviceImageTy &Image, const ELF64LE::Sym &Symbol,
+    const ELF64LE::Shdr &Section, GlobalTy &ImageGlobal) {
+
+  // The global's address is computed as the image begin + the ELF section
+  // offset + the ELF symbol value.
+  ImageGlobal.setPtr((char *)Image.getStart() + Section.sh_offset +
+                     Symbol.st_value);
+
+  // Set the global's size.
+  ImageGlobal.setSize(Symbol.st_size);
+
+  return Plugin::success();
+}
+
 Error GenericGlobalHandlerTy::moveGlobalBetweenDeviceAndHost(
     GenericDeviceTy &Device, DeviceImageTy &Image, const GlobalTy &HostGlobal,
     bool Device2Host) {
 
   GlobalTy DeviceGlobal(HostGlobal.getName(), HostGlobal.getSize());
 
   // Get the metadata from the global on the device.
   if (auto Err = getGlobalMetadataFromDevice(Device, Image, DeviceGlobal))
return Plugin::error("Failed ELF lookup of global '%s': %s",
                          ImageGlobal.getName().data(),
                          toString(SymOrErr.takeError()).data());
 
   if (!*SymOrErr)
     return Plugin::error("Failed to find global symbol '%s' in the ELF image",
                          ImageGlobal.getName().data());
 
   // Get the section to which the symbol belongs.
-  auto SymSecOrErr = ELFObj->getELFFile().getSection((*SymOrErr)->st_shndx);
-  if (!SymSecOrErr)
+  auto SecOrErr = ELFObj->getELFFile().getSection((*SymOrErr)->st_shndx);
+  if (!SecOrErr)
     return Plugin::error("Failed to get ELF section from global '%s': %s",
                          ImageGlobal.getName().data(),
-                         toString(SymOrErr.takeError()).data());
+                         toString(SecOrErr.takeError()).data());
 
-  // Save the global symbol's address and size. The address of the global is the
-  // image base address + the section offset + the symbol value.
-  ImageGlobal.setPtr((char *)Image.getStart() + (*SymSecOrErr)->sh_offset +
-                     (*SymOrErr)->st_value);
-  ImageGlobal.setSize((*SymOrErr)->st_size);
-
-  return Plugin::success();
+  // Setup the global symbol's address and size.
+  return getGlobalMetadataFromELF(Image, **SymOrErr, **SecOrErr, ImageGlobal);
 }
 
 Error GenericGlobalHandlerTy::readGlobalFromImage(GenericDeviceTy &Device,
                                                   DeviceImageTy &Image,
                                                   const GlobalTy &HostGlobal) {
 
   GlobalTy ImageGlobal(HostGlobal.getName(), -1);
   if (auto Err = getGlobalMetadataFromImage(Device, Image, ImageGlobal))