Look through variables when computing relocations.

Given

bar = foo + 4
	.long bar

MC would eat the 4. GNU as includes it in the relocation. The rule seems to be
that a variable that defines a symbol is used in the relocation and one that
does not define a symbol is evaluated and the result included in the relocation.

Fixing this unfortunately required some other changes:

* Since the variable is now evaluated, it would prevent the ELF writer from
  noticing the weakref marker the elf streamer uses. This patch then replaces
  that with a VariantKind in MCSymbolRefExpr.

* Using VariantKind then requires us to look past other VariantKind to see

	.weakref	bar,foo
	call	bar@PLT

  doing this also fixes

	zed = foo +2
	call zed@PLT

  so that is a good thing.

* Looking past VariantKind means that the relocation selection has to use
  the fixup instead of the target.

This is a reboot of the previous fixes for MC. I will watch the sanitizer
buildbot and wait for a build before adding back the previous fixes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204294 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 3 deletions

diff --git a/lib/MC/MCELFStreamer.cpp b/lib/MC/MCELFStreamer.cpp
index 5f6a889769..d07ef9e698 100644
--- a/lib/MC/MCELFStreamer.cpp
+++ b/lib/MC/MCELFStreamer.cpp
@@ -99,9 +99,8 @@ void MCELFStreamer::ChangeSection(const MCSection *Section,
 
 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
   getAssembler().getOrCreateSymbolData(*Symbol);
-  MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
-  AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
-  const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
+  const MCExpr *Value = MCSymbolRefExpr::Create(
+      Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
   Alias->setVariableValue(Value);
 }