[lldb] Declare extern template instantiation to fix linking issues.

NativeProcessELF::GetELFImageInfoAddress<...>() is declared in NativeProcessELF.h, but only defined in NativeProcessELF.cpp. Via some optimized builds (e.g. thinlto), this instantiation may be removed when it is used in a different TU (NativeProcessELFTest.cpp).

Author: rupprecht

lldb/source/Plugins/Process/POSIX/NativeProcessELF.cpp

@@ -107,6 +107,11 @@ lldb::addr_t NativeProcessELF::GetELFImageInfoAddress() {
   return LLDB_INVALID_ADDRESS;
 }
 
+template lldb::addr_t NativeProcessELF::GetELFImageInfoAddress<
+    llvm::ELF::Elf32_Ehdr, llvm::ELF::Elf32_Phdr, llvm::ELF::Elf32_Dyn>();
+template lldb::addr_t NativeProcessELF::GetELFImageInfoAddress<
+    llvm::ELF::Elf64_Ehdr, llvm::ELF::Elf64_Phdr, llvm::ELF::Elf64_Dyn>();
+
 template <typename T>
 llvm::Expected<SVR4LibraryInfo>
 NativeProcessELF::ReadSVR4LibraryInfo(lldb::addr_t link_map_addr) {

lldb/source/Plugins/Process/POSIX/NativeProcessELF.h

@@ -48,6 +48,14 @@ class NativeProcessELF : public NativeProcessProtocol {
   llvm::Optional<lldb::addr_t> m_shared_library_info_addr;
 };
 
+// Explicitly declare the two 32/64 bit templates that NativeProcessELF.cpp will
+// define. This allows us to keep the template definition here and usable
+// elsewhere.
+extern template lldb::addr_t NativeProcessELF::GetELFImageInfoAddress<
+    llvm::ELF::Elf32_Ehdr, llvm::ELF::Elf32_Phdr, llvm::ELF::Elf32_Dyn>();
+extern template lldb::addr_t NativeProcessELF::GetELFImageInfoAddress<
+    llvm::ELF::Elf64_Ehdr, llvm::ELF::Elf64_Phdr, llvm::ELF::Elf64_Dyn>();
+
 } // namespace lldb_private
 
-#endif
+#endif