AArch64: Emit PAuth ifuncs into the same comdat as the containing global.

PAuth ifuncs contain a relocation pointing to the section they are
relocating (the place), so they need to be in the same comdat in order
to avoid relocations pointing to discarded sections.

Reviewers: atrosinenko, kovdan01, fmayer

Reviewed By: fmayer

Pull Request: #170944

Author: pcc

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -2484,9 +2484,15 @@ const MCExpr *AArch64AsmPrinter::emitPAuthRelocationAsIRelative(
   OutStreamer->emitLabel(Place);
   OutStreamer->pushSection();
 
+  const MCSymbolELF *Group =
+      static_cast<MCSectionELF *>(OutStreamer->getCurrentSectionOnly())
+          ->getGroup();
+  auto Flags = ELF::SHF_ALLOC | ELF::SHF_EXECINSTR;
+  if (Group)
+    Flags |= ELF::SHF_GROUP;
   OutStreamer->switchSection(OutStreamer->getContext().getELFSection(
-      ".text.startup", ELF::SHT_PROGBITS, ELF::SHF_ALLOC | ELF::SHF_EXECINSTR,
-      0, "", true, PAuthIFuncNextUniqueID++, nullptr));
+      ".text.startup", ELF::SHT_PROGBITS, Flags, 0, Group, true,
+      Group ? MCSection::NonUniqueID : PAuthIFuncNextUniqueID++, nullptr));
 
   MCSymbol *IRelativeSym =
       OutStreamer->getContext().createLinkerPrivateSymbol("pauth_ifunc");

llvm/test/CodeGen/AArch64/ptrauth-irelative.ll

@@ -93,3 +93,9 @@
 ; CHECK-NEXT: .section .rodata
 ; CHECK-NEXT: .xword [[FUNC]]@FUNCINIT
 @globalref8 = constant ptr ptrauth (ptr getelementptr (i8, ptr @global, i64 8), i32 2, i64 5, ptr null), align 8
+
+$comdat = comdat any
+@comdat = constant ptr ptrauth (ptr null, i32 2, i64 1, ptr null), align 8, comdat
+; CHECK: comdat:
+; CHECK-NEXT: [[PLACE:.*]]:
+; CHECK-NEXT: .section	.text.startup,"axG",@progbits,comdat,comdat