[ELF][MIPS] Check for overflow when writing R_MIPS_CALL16 and R_MIPS_TLS_GOTTPREL

[arichardson]

Summary

These are 16 bit relocations and not part of a HI/LO pair so we need to
check that they don't overflow.

[sdardis]

+llvm-commits

Patches have to be CC'd to the relevant commits list.

[arichardson]

Added a test case.

I noticed that test case no longer works with https://reviews.llvm.org/D31528 (Multi-GOT) and I'm not sure how to create one that works with it.

[atanasyan]

LGTM

I think it will be impossible to write a test case for this change when multi-GOT is implemented. The only option is to implement a "debug" command line option for disabling multi-GOT. Additional flag is redundant, but my patch has mips-got-size flag. I consider to treat a zero argument of this flag as a special value.

ELF/Arch/Mips.cpp

void MIPS<ELFT>::relocateOne(uint8_t *Loc, uint32_t Type, uint64_t Val) const {
   case R_MICROMIPS_GOT16:
     if (Config->Relocatable) {
       writeMicroRelocation32<E>(Loc, Val + 0x8000, 16, 16);
     } else {
       checkInt<16>(Loc, Val, Type);
       writeMicroRelocation32<E>(Loc, Val, 16, 0);
     }
     break;
+  case R_MIPS_CALL16:
   case R_MIPS_GOT_DISP:
   case R_MIPS_GOT_PAGE:
   case R_MIPS_GPREL16:
   case R_MIPS_TLS_GD:
+  case R_MIPS_TLS_GOTTPREL:
   case R_MIPS_TLS_LDM:
     checkInt<16>(Loc, Val, Type);
     LLVM_FALLTHROUGH;
-  case R_MIPS_CALL16:
   case R_MIPS_CALL_LO16:
   case R_MIPS_GOT_LO16:
   case R_MIPS_GOT_OFST:
   case R_MIPS_LO16:
   case R_MIPS_PCLO16:
   case R_MIPS_TLS_DTPREL_LO16:
-  case R_MIPS_TLS_GOTTPREL:
   case R_MIPS_TLS_TPREL_LO16:
     writeRelocation<E>(Loc, Val, 16, 0);
     break;
   case R_MICROMIPS_GOT_DISP:
   case R_MICROMIPS_GOT_PAGE:
   case R_MICROMIPS_GPREL16:
   case R_MICROMIPS_TLS_GD:
   case R_MICROMIPS_TLS_LDM: