Fix --filetype=iasm non-pc-rel fixup offsets (double counted).

src/IceELFSection.h

 //===- subzero/src/IceELFSection.h - Model of ELF sections ------*- C++ -*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 344 matching lines @@
   for (const AssemblerFixup &Fixup : Fixups) {
     const ELFSym *Symbol;
     if (Fixup.isNullSymbol())
       Symbol = SymTab->getNullSymbol();
     else
       Symbol = SymTab->findSymbol(Fixup.symbol(&Ctx));
     if (!Symbol)
       llvm::report_fatal_error("Missing symbol mentioned in reloc");
 
     if (IsELF64) {
+      llvm_unreachable(
+          "Not tested -- check that Fixup.offset() is correct even for pc-rel");
       Elf64_Rela Rela;
       Rela.r_offset = Fixup.position();
       Rela.setSymbolAndType(Symbol->getNumber(), Fixup.kind());
       Rela.r_addend = Fixup.offset();

[jvoung (off chromium), 2015/07/20 23:29:05]

This doesn't consult the buffer's contents, so we'll probably run into a bug if
the ConstantRelocatable object for a function call doesn't hold the true offset
(and only the buffer holds that offset), even if the offset is kind of silly
(e.g., the -4 you would get from pcrel call).

       Str.writeAddrOrOffset<IsELF64>(Rela.r_offset);
       Str.writeELFXword<IsELF64>(Rela.r_info);
       Str.writeELFXword<IsELF64>(Rela.r_addend);
     } else {
       Elf32_Rel Rel;
       Rel.r_offset = Fixup.position();
       Rel.setSymbolAndType(Symbol->getNumber(), Fixup.kind());
       Str.writeAddrOrOffset<IsELF64>(Rel.r_offset);
       Str.writeELFWord<IsELF64>(Rel.r_info);
     }
   }
 }
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICEELFSECTION_H