[RelocationResolver] Support new LoongArch relocs

[xen0n]

Summary

Support for applicable LAELF v20230519 relocs are added, minus the
couple of ULEB128 relocs that cannot be supported with the current API:
a buffer or stream is required to be able to decode/encode LEB128
values, while currently only LocData is available which is just an
integer.

A previous oversight that led to always-zero LocData for LoongArch is
also fixed.

[MaskRay]

Some relocations can be tested like D134164

llvm/lib/Object/RelocationResolver.cpp

 }
 
 static bool supportsLoongArch(uint64_t Type) {
   switch (Type) {
   case ELF::R_LARCH_NONE:
   case ELF::R_LARCH_32:
   case ELF::R_LARCH_32_PCREL:
   case ELF::R_LARCH_64:
+  case ELF::R_LARCH_64_PCREL:
+  case ELF::R_LARCH_ADD6:
+  case ELF::R_LARCH_SUB6:
   case ELF::R_LARCH_ADD8:
   case ELF::R_LARCH_SUB8:
   case ELF::R_LARCH_ADD16:
   case ELF::R_LARCH_SUB16:
   case ELF::R_LARCH_ADD32:
   case ELF::R_LARCH_SUB32:
   case ELF::R_LARCH_ADD64:
   case ELF::R_LARCH_SUB64:
     return true;
+  case ELF::R_LARCH_ADD_ULEB128:
+  case ELF::R_LARCH_SUB_ULEB128:
+    // TODO: Cannot be supported with the current API: LEB128 requires a
+    // stream for I/O.
+    return false;
   default:
     return false;
   }
 }
 
 static uint64_t resolveLoongArch(uint64_t Type, uint64_t Offset, uint64_t S,
                                  uint64_t LocData, int64_t Addend) {
   switch (Type) {
   case ELF::R_LARCH_NONE:
     return LocData;
   case ELF::R_LARCH_32:
     return (S + Addend) & 0xFFFFFFFF;
   case ELF::R_LARCH_32_PCREL:
     return (S + Addend - Offset) & 0xFFFFFFFF;
   case ELF::R_LARCH_64:
     return S + Addend;
+  case ELF::R_LARCH_64_PCREL:
+    return S + Addend - Offset;
+  case ELF::R_LARCH_ADD6:
+    return (LocData & 0xC0) | (((LocData & 0x3F) + (S + Addend)) & 0x3F);
+  case ELF::R_LARCH_SUB6:
+    return (LocData & 0xC0) | (((LocData & 0x3F) - (S + Addend)) & 0x3F);
   case ELF::R_LARCH_ADD8:
     return (LocData + (S + Addend)) & 0xFF;
   case ELF::R_LARCH_SUB8:
     return (LocData - (S + Addend)) & 0xFF;
   case ELF::R_LARCH_ADD16:
     return (LocData + (S + Addend)) & 0xFFFF;
   case ELF::R_LARCH_SUB16:
     return (LocData - (S + Addend)) & 0xFFFF;
if (Obj->isELF()) {
         if (auto *Elf32BEObj = dyn_cast<ELF32BEObjectFile>(Obj))
           return Elf32BEObj->getRelSection(R.getRawDataRefImpl())->sh_type;
         auto *Elf64BEObj = cast<ELF64BEObjectFile>(Obj);
         return Elf64BEObj->getRelSection(R.getRawDataRefImpl())->sh_type;
       };
 
       if (GetRelSectionType() == ELF::SHT_RELA) {
         Addend = getELFAddend(R);
-        // RISCV relocations use both LocData and Addend.
-        if (Obj->getArch() != Triple::riscv32 &&
+        // LoongArch and RISCV relocations use both LocData and Addend.
+        if (Obj->getArch() != Triple::loongarch32 &&
+            Obj->getArch() != Triple::loongarch64 &&
+            Obj->getArch() != Triple::riscv32 &&
             Obj->getArch() != Triple::riscv64)
           LocData = 0;
       }
     }
 
     return Resolver(R.getType(), R.getOffset(), S, LocData, Addend);
   }