[llvm] [llvm] Support IFuncs on Darwin platforms (PR #73686)

[Jon Roelofs via llvm-commits]

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@@ -1809,6 +1838,292 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) {
   EmitToStreamer(*OutStreamer, TmpInst);
 }
 
+void AArch64AsmPrinter::emitLinkerSymbolResolver(Module &M,
+                                                 const GlobalIFunc &GI) {
+  OutStreamer->switchSection(OutContext.getObjectFileInfo()->getTextSection());
+
+  MCSymbol *Name = getSymbol(&GI);
+
+  // NOTE: non-global .symbol_resolvers are not yet supported by Darwin linkers
+
+  if (GI.hasExternalLinkage() || !MAI->getWeakRefDirective())
+    OutStreamer->emitSymbolAttribute(Name, MCSA_Global);
+  else if (GI.hasWeakLinkage() || GI.hasLinkOnceLinkage())
+    OutStreamer->emitSymbolAttribute(Name, MCSA_WeakReference);
+  else
+    assert(GI.hasLocalLinkage() && "Invalid ifunc linkage");
+
+  OutStreamer->emitCodeAlignment(Align(4), STI);
+  OutStreamer->emitLabel(Name);
+  OutStreamer->emitSymbolAttribute(Name, MCSA_SymbolResolver);
+  emitVisibility(Name, GI.getVisibility());
+
+  // ld-prime does not seem to support aliases of symbol resolvers, so we have
+  // to tail call the resolver manually.
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jroelofs wrote:

IIUC it is appropriate to mention this here, but not in the actual diff:

rdar://118480251 (Aliased .symbol_resolver's)

https://github.com/llvm/llvm-project/pull/73686