[WebAssembly] Add support for weak symbols in the binary format

This also introduces the updated format for the
"linking" section which can represent extra
symbol information.  See:
https://github.com/WebAssembly/tool-conventions/pull/10

Differential Revision: https://reviews.llvm.org/D34019

llvm-svn: 305769

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCWasmStreamer.cpp b/llvm/lib/MC/MCWasmStreamer.cpp
index 59b62b8d37c..02fa070f0c5 100644
--- a/llvm/lib/MC/MCWasmStreamer.cpp
+++ b/llvm/lib/MC/MCWasmStreamer.cpp
@@ -98,18 +98,30 @@ bool MCWasmStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
   case MCSA_WeakDefAutoPrivate:
   case MCSA_Invalid:
   case MCSA_IndirectSymbol:
+  case MCSA_Hidden:
     return false;
+
+  case MCSA_Weak:
+  case MCSA_WeakReference:
+    Symbol->setWeak(true);
+    Symbol->setExternal(true);
+    break;
+
   case MCSA_Global:
     Symbol->setExternal(true);
     break;
+
   case MCSA_ELF_TypeFunction:
     Symbol->setIsFunction(true);
     break;
+
   case MCSA_ELF_TypeObject:
     Symbol->setIsFunction(false);
     break;
+
   default:
     // unrecognized directive
+    llvm_unreachable("unexpected MCSymbolAttr");
     return false;
   }