[mips][mcjit] Add support for R_MIPS_PC32.

[dsanders]

Summary

This allows us to resolve relocations for DW_EH_PE_pcrel TType encodings
in the exception handling LSDA.

Also fixed a nearby typo.

[vkalintiris]

LGTM.

lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

 }
 
 void RuntimeDyldELF::resolveMIPSRelocation(const SectionEntry &Section,
                                            uint64_t Offset, uint32_t Value,
                                            uint32_t Type, int32_t Addend) {
   uint32_t *TargetPtr = (uint32_t *)(Section.Address + Offset);
   Value += Addend;
 
-  DEBUG(dbgs() << "resolveMipselocation, LocalAddress: "
+  DEBUG(dbgs() << "resolveMIPSRelocation, LocalAddress: "
                << Section.Address + Offset << " FinalAddress: "
                << format("%p", Section.LoadAddress + Offset) << " Value: "
                << format("%x", Value) << " Type: " << format("%x", Type)
                << " Addend: " << format("%x", Addend) << "\n");
 
   switch (Type) {
   default:
     llvm_unreachable("Not implemented relocation type!");
     break;
   case ELF::R_MIPS_32:
     *TargetPtr = Value;
     break;
   case ELF::R_MIPS_26:
     *TargetPtr = ((*TargetPtr) & 0xfc000000) | ((Value & 0x0fffffff) >> 2);
     break;
   case ELF::R_MIPS_HI16:
     // Get the higher 16-bits. Also add 1 if bit 15 is 1.
     *TargetPtr =
       ((*TargetPtr) & 0xffff0000) | (((Value + 0x8000) >> 16) & 0xffff);
     break;
   case ELF::R_MIPS_LO16:
     *TargetPtr = ((*TargetPtr) & 0xffff0000) | (Value & 0xffff);
     break;
+  case ELF::R_MIPS_PC32:
+    uint32_t FinalAddress = (Section.LoadAddress + Offset);
+    writeBytesUnaligned(Value + Addend - FinalAddress, (uint8_t *)TargetPtr, 4);
+    break;
   }
 }
 
 void RuntimeDyldELF::setMipsABI(const ObjectFile &Obj) {
   if (!StringRef(Triple::getArchTypePrefix(Arch)).equals("mips")) {
     IsMipsO32ABI = false;
     IsMipsN64ABI = false;
     return;

test/ExecutionEngine/RuntimeDyld/Mips/ELF_O32_PIC_relocations.s

 # RUN: llvm-mc -triple=mipsel-unknown-linux -relocation-model=pic -code-model=small -filetype=obj -o %T/test_ELF_O32.o %s
 # RUN: llc -mtriple=mipsel-unknown-linux -relocation-model=pic -filetype=obj -o %T/test_ELF_ExternalFunction_O32.o %S/Inputs/ExternalFunction.ll
 # RUN: llvm-rtdyld -triple=mipsel-unknown-linux -verify -map-section test_ELF_O32.o,.text=0x1000 -map-section test_ELF_ExternalFunction_O32.o,.text=0x10000 -check=%s %/T/test_ELF_O32.o %T/test_ELF_ExternalFunction_O32.o
 
 # R!N: llvm-mc -triple=mips-unknown-linux -relocation-model=pic -code-model=small -filetype=obj -o %T/test_ELF_O32.o %s
 # R!N: llc -mtriple=mips-unknown-linux -relocation-model=pic -filetype=obj -o %T/test_ELF_ExternalFunction_O32.o %S/Inputs/ExternalFunction.ll
 # R!N: llvm-rtdyld -triple=mips-unknown-linux -verify -map-section test_ELF_O32.o,.text=0x1000 -map-section test_ELF_ExternalFunction_O32.o,.text=0x10000 -check=%s %/T/test_ELF_O32.o %T/test_ELF_ExternalFunction_O32.o
 
         .data
 # rtdyld-check: *{4}R_MIPS_32 = foo
 R_MIPS_32:
         .word foo
 # rtdyld-check: *{4}(R_MIPS_32+4) = foo
         .4byte foo
+# rtdyld-check: *{4}(R_MIPS_PC32) = foo - R_MIPS_PC32
+R_MIPS_PC32:
+        .word foo-.
+# rtdyld-check: *{4}(R_MIPS_PC32 + 4) = foo - tmp1
+tmp1:
+        .4byte foo-tmp1
 
   .text
   .abicalls
   .nan  legacy
   .text
   .set  nomicromips
   .set  nomips16
   .set  noreorder