[MIPS] Don't emit R_(MICRO)MIPS_JALR relocations against data symbols

The R_(MICRO)MIPS_JALR optimization only works when used against functions.
Using the relocation against a data symbol (e.g. function pointer) will
cause some linkers that don't ignore the hint in this case (e.g. LLD prior
to commit 5bab291b7b) to generate a relative branch to the data symbol
which crashes at run time. Before this patch, LLVM was erroneously emitting
these relocations against local-dynamic TLS function pointers and global
function pointers with internal visibility.

Reviewers: atanasyan, jrtc27, vstefanovic
Reviewed By: atanasyan
Differential Revision: https://reviews.llvm.org/D72571

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/Mips/MipsISelLowering.cpp b/llvm/lib/Target/Mips/MipsISelLowering.cpp
index ea242b4d46b..46b1f35a6fc 100644
--- a/llvm/lib/Target/Mips/MipsISelLowering.cpp
+++ b/llvm/lib/Target/Mips/MipsISelLowering.cpp
@@ -3111,6 +3111,14 @@ void MipsTargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
       StringRef Sym;
       if (const GlobalAddressSDNode *G =
               dyn_cast_or_null<const GlobalAddressSDNode>(TargetAddr)) {
+        // We must not emit the R_MIPS_JALR relocation against data symbols
+        // since this will cause run-time crashes if the linker replaces the
+        // call instruction with a relative branch to the data symbol.
+        if (!isa<Function>(G->getGlobal())) {
+          LLVM_DEBUG(dbgs() << "Not adding R_MIPS_JALR against data symbol "
+                            << G->getGlobal()->getName() << "\n");
+          return;
+        }
         Sym = G->getGlobal()->getName();
       }
       else if (const ExternalSymbolSDNode *ES =
@@ -3123,6 +3131,7 @@ void MipsTargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
 
       MachineFunction *MF = MI.getParent()->getParent();
       MCSymbol *S = MF->getContext().getOrCreateSymbol(Sym);
+      LLVM_DEBUG(dbgs() << "Adding R_MIPS_JALR against " << Sym << "\n");
       MI.addOperand(MachineOperand::CreateMCSymbol(S, MipsII::MO_JALR));
     }
   }