[llvm] c989993 - [XCOFF] Fix link errors from explicit template instantiation

[Reid Kleckner via llvm-commits]

Author: Reid Kleckner
Date: 2019-11-07T09:29:48-08:00
New Revision: c989993ba1a666f04f7aee7df51d9f4de0588b71

URL: https://github.com/llvm/llvm-project/commit/c989993ba1a666f04f7aee7df51d9f4de0588b71
DIFF: https://github.com/llvm/llvm-project/commit/c989993ba1a666f04f7aee7df51d9f4de0588b71.diff

LOG: [XCOFF] Fix link errors from explicit template instantiation

I happen to be using clang-cl+lld-link locally, and I get these link
errors:

lld-link: error: undefined symbol: public: unsigned short __cdecl llvm::object::XCOFFSectionHeader<struct llvm::object::XCOFFSectionHeader64>::getSectionType(void) const
>>> referenced by C:\src\llvm-project\llvm\tools\llvm-readobj\XCOFFDumper.cpp:106
>>>               tools\llvm-readobj\CMakeFiles\llvm-readobj.dir\XCOFFDumper.cpp.obj:(public: virtual void __cdecl `anonymous namespace'::XCOFFDumper::printSectionHeaders(void))

I suspect this is because the explicit template instaniation appears
before the inline method definitions in the .cpp file, so they aren't
available at the point of instantiation. Move the explicit instantiation
later.

Also, forward declare the explicit instantiation for good measure.

Added: 
    

Modified: 
    llvm/include/llvm/Object/XCOFFObjectFile.h
    llvm/lib/Object/XCOFFObjectFile.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Object/XCOFFObjectFile.h b/llvm/include/llvm/Object/XCOFFObjectFile.h
index 4f80297b04c6..fcdbf7a8095c 100644
--- a/llvm/include/llvm/Object/XCOFFObjectFile.h
+++ b/llvm/include/llvm/Object/XCOFFObjectFile.h
@@ -60,6 +60,12 @@ template <typename T> struct XCOFFSectionHeader {
   bool isReservedSectionType() const;
 };
 
+// Explicit extern template declarations.
+struct XCOFFSectionHeader32;
+struct XCOFFSectionHeader64;
+extern template struct XCOFFSectionHeader<XCOFFSectionHeader32>;
+extern template struct XCOFFSectionHeader<XCOFFSectionHeader64>;
+
 struct XCOFFSectionHeader32 : XCOFFSectionHeader<XCOFFSectionHeader32> {
   char Name[XCOFF::NameSize];
   support::ubig32_t PhysicalAddress;

diff  --git a/llvm/lib/Object/XCOFFObjectFile.cpp b/llvm/lib/Object/XCOFFObjectFile.cpp
index 5ca2a6a03f04..3ea42bb8b0e0 100644
--- a/llvm/lib/Object/XCOFFObjectFile.cpp
+++ b/llvm/lib/Object/XCOFFObjectFile.cpp
@@ -61,6 +61,10 @@ bool XCOFFSectionHeader<T>::isReservedSectionType() const {
   return getSectionType() & SectionFlagsReservedMask;
 }
 
+// Explictly instantiate template classes.
+template struct XCOFFSectionHeader<XCOFFSectionHeader32>;
+template struct XCOFFSectionHeader<XCOFFSectionHeader64>;
+
 bool XCOFFRelocation32::isRelocationSigned() const {
   return Info & XR_SIGN_INDICATOR_MASK;
 }