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

[pcc]

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.

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Peter Collingbourne (pcc)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/170944.diff

2 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp (+7-2)
• (modified) llvm/test/CodeGen/AArch64/ptrauth-irelative.ll (+6)

diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index 8267414e78955..8ef985451a4c1 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -2484,9 +2484,14 @@ const MCExpr *AArch64AsmPrinter::emitPAuthRelocationAsIRelative(
   OutStreamer->emitLabel(Place);
   OutStreamer->pushSection();
 
+  const MCSymbolELF *Group =
+      static_cast<MCSectionELF *>(OutStreamer->getCurrentSectionOnly())
+          ->getGroup();
   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,
+      ELF::SHF_ALLOC | ELF::SHF_EXECINSTR | (Group ? ELF::SHF_GROUP : 0), 0,
+      Group, true, Group ? MCSection::NonUniqueID : PAuthIFuncNextUniqueID++,
+      nullptr));
 
   MCSymbol *IRelativeSym =
       OutStreamer->getContext().createLinkerPrivateSymbol("pauth_ifunc");
diff --git a/llvm/test/CodeGen/AArch64/ptrauth-irelative.ll b/llvm/test/CodeGen/AArch64/ptrauth-irelative.ll
index 4ee1c19a86490..6a291497d6c46 100644
--- a/llvm/test/CodeGen/AArch64/ptrauth-irelative.ll
+++ b/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