svn commit: r326897 - head/contrib/llvm/tools/lld/ELF

[Ed Maste]

Author: emaste
Date: Sat Dec 16 14:26:11 2017
New Revision: 326897
URL: https://svnweb.freebsd.org/changeset/base/326897

Log:
  lld: Slightly simplify code and add comment.
  
  Cherry-pick lld r315658 by Rui Ueyama:
      This is not a mechanical transformation. Even though I believe this
      patch is correct, I'm not 100% sure if lld with this patch behaves
      exactly the same way as before on all edge cases. At least all tests
      still pass.
  
      I'm submitting this patch because it took almost a day to understand
      this function, and I don't want to lose it.
  
  This fixes jemalloc assertion failures observed at startup with i386
  binaries and an lld-linked libc.so.
  
  Reviewed by:	dim
  Obtained from:	LLVM r315658
  MFC after:	1 week
  Sponsored by:	The FreeBSD Foundation
  Differential Revision:	https://reviews.freebsd.org/D13503

Modified:
  head/contrib/llvm/tools/lld/ELF/Relocations.cpp

Modified: head/contrib/llvm/tools/lld/ELF/Relocations.cpp
==============================================================================
--- head/contrib/llvm/tools/lld/ELF/Relocations.cpp	Sat Dec 16 12:23:59 2017	(r326896)
+++ head/contrib/llvm/tools/lld/ELF/Relocations.cpp	Sat Dec 16 14:26:11 2017	(r326897)
@@ -790,13 +790,31 @@ static void addGotEntry(SymbolBody &Sym, bool Preempti
     DynType = Target->GotRel;
   }
 
-  bool Constant = !Preemptible && (!Config->Pic || isAbsolute(Sym));
-  if (!Constant)
+  // If a GOT slot value can be calculated at link-time, which is now,
+  // we can just fill that out.
+  //
+  // (We don't actually write a value to a GOT slot right now, but we
+  // add a static relocation to a Relocations vector so that
+  // InputSection::relocate will do the work for us. We may be able
+  // to just write a value now, but it is a TODO.)
+  bool IsLinkTimeConstant = !Preemptible && (!Config->Pic || isAbsolute(Sym));
+  if (IsLinkTimeConstant) {
+    InX::Got->Relocations.push_back({Expr, DynType, Off, 0, &Sym});
+  } else {
+    // Otherwise, we emit a dynamic relocation to .rel[a].dyn so that
+    // the GOT slot will be fixed at load-time.
     In<ELFT>::RelaDyn->addReloc(
         {DynType, InX::Got, Off, !Preemptible, &Sym, 0});
 
-  if (Constant || (!Config->IsRela && !Preemptible))
-    InX::Got->Relocations.push_back({Expr, DynType, Off, 0, &Sym});
+    // REL type relocations don't have addend fields unlike RELAs, and
+    // their addends are stored to the section to which they are applied.
+    // So, store addends if we need to.
+    //
+    // This is ugly -- the difference between REL and RELA should be
+    // handled in a better way. It's a TODO.
+    if (!Config->IsRela)
+      InX::Got->Relocations.push_back({R_ABS, Target->GotRel, Off, 0, &Sym});
+  }
 }
 
 // The reason we have to do this early scan is as follows