[WIP] Generate weak export table entries for weak function symbols.

Author: resistor

llvm/lib/Target/RISCV/RISCVAsmPrinter.cpp

@@ -715,6 +715,8 @@ void RISCVAsmPrinter::emitEndOfAsmFile(Module &M) {
       // export different static things.
       if (Entry.Fn.hasExternalLinkage() && !Entry.forceLocal)
         OutStreamer->emitSymbolAttribute(Sym, MCSA_Global);
+      else if (Entry.Fn.isWeakForLinker() && !Entry.forceLocal)
+          OutStreamer->emitSymbolAttribute(Sym, MCSA_Weak);
       OutStreamer->emitValueToAlignment(Align(4));
       OutStreamer->emitLabel(Sym);
       emitLabelDifference(Entry.FnSym, CompartmentStartSym, 2);
@@ -741,6 +743,8 @@ void RISCVAsmPrinter::emitEndOfAsmFile(Module &M) {
         OutStreamer->emitSymbolAttribute(AliasExportSym, MCSA_ELF_TypeObject);
         if (GA->hasExternalLinkage() && !Entry.forceLocal)
           OutStreamer->emitSymbolAttribute(AliasExportSym, MCSA_Global);
+        else if (GA->isWeakForLinker() && !Entry.forceLocal)
+          OutStreamer->emitSymbolAttribute(AliasExportSym, MCSA_Weak);
         OutStreamer->emitAssignment(AliasExportSym,
                                     MCSymbolRefExpr::create(Sym, C));
         OutStreamer->emitELFSize(AliasExportSym, MCConstantExpr::create(4, C));