[MIPS] Initial support of microMIPS code linking

[atanasyan]

Summary

The patch implements initial support of microMIPS code linking:

• Handle microMIPS specific relocations.
• Emit both R1-R5 and R6 microMIPS PLT records.

For now linking mixed set of regular and microMIPS object files is not supported. Also the patch does not handle (setup and clear) the least-significant bit of an address which is utilized as the ISA mode bit and allows to make jump between regular and microMIPS code without any thunks.

[ruiu]

ELF/Arch/Mips.cpp

179–180

So this expression is all R_MICROMIPS_* relocations except ones that have 1 or 2 byte opcodes instead of 4 bytes, right? It might be helpful to add a comment about that because it is not obvious that R_MICROMIPS_26_S1 is the first relocation type and R_MICROMIPS_PC19_S2 the last for R_MICROMIPS_* relocations.

190–192

Is this the same as swapping the first two bytes with the following two bytes? If so, is this different from unshuffle?

Can this be something like this?

uint16_t *A = (uint16_t *)Loc;
std::swap(A[0], A[1]);

201

BSIZE and SHIFT can be passed as function arguments instead of template arguments.

291

Do you need this?

488

nit: add {}

624–625

Hmm, it looks like you shuffle bytes and then restore the bytes at end of the function. Looks like it's a bit tricky. Is it possible to define a writeRelocation function for R_MICROMIPS_* and shuffle bytes in that function?

[atanasyan]

• Remove needShuffling function.
• Remove separate shuffle and unshuffle functions and move the code into the writeMicroRelocation32 routine. Now we "unsuffle" data when read implicit addend and "unshuffle" and then "shuffle" data back when writing result of microMIPS relocation.
• Fix shuffling of 16-bit words. Do it iif target binary is little-endian.
• Keep memset calls in writePltHeader and writePlt methods. In short, size of actual PLT entry can be less than PltEntrySize and we need to fill unused space by "nops". When we initialize PltEntrySize and PltHeaderSize fields we do not know what kind of PLT header/entry we will need to create: regular of microMIPS. These entries have different sizes. Ideally, if a PLT entry is referenced by microMIPS code only this entry should contain microMIPS code, if a PLT entry is referenced by regular code this entry should contain regular code. In a "mixed" case the PLT entry can be either microMIPS or regular, but each "cross-mode-call" has additional cost. Now LLD cannot: a) maintain PLT records with different sizes; b) record type of references (regular / microMIPS) for a PLT entry. To simplify the patch I assume that usually the most or all code have the same type regular or microMIPS. I allocate space for the largest PLT header/entry, but at the time of PLT creation I write either regular or microMIPS entries only. In the last case PLT has gaps which needs to be filled by "nops".

[ruiu]

ELF/Arch/Mips.cpp

181–184

I don't believe this is correct as I seems to be violating the strict aliasing rule. I'd do

return (V << 16) | (V >> 16);

291

Is this needed?

[atanasyan]

ELF/Arch/Mips.cpp

181–184

OK

291

In short - yes, the memset call is required to overwrite trap instructions 0xefefefef. Here is a slightly modified quote from my previous reply:

Keep memset calls in writePltHeader and writePlt methods. In short, size of actual PLT entry can be less than PltEntrySize and we need to fill unused space by "nops". When we initialize PltEntrySize and PltHeaderSize fields we do not know what kind of PLT header/entry we will need to create: regular of microMIPS. These entries have different sizes. Ideally, if a PLT entry is referenced by microMIPS code only this entry should contain microMIPS code, if a PLT entry is referenced by regular code this entry should contain regular code. In a "mixed" case the PLT entry can be either microMIPS or regular, but each "cross-mode-call" has additional cost. Now LLD cannot: a) maintain PLT records with different sizes; b) record type of references (regular / microMIPS) for a PLT entry. To simplify the patch I assume that usually the most or all code have the same type regular or microMIPS. I allocate space for the largest PLT header/entry, but at the time of PLT creation I write either regular or microMIPS entries only. In the last case PLT has gaps filled by 0xefefefef which needs to be filled by "nops".

[ruiu]

ELF/Arch/Mips.cpp

291

Thanks. Can you add a comment saying that this is to overwrite trap instructions written by Writer::writeTrapInstr?

[atanasyan]

• Added comments to explain memset calls
• Fixed violating the strict aliasing rule.

[ruiu]

ELF/Arch/Mips.cpp

239

Add a blank line here so that it is clear that the comment is saying only about the memset.

293

Ditto

488

?

519

Since the following case body is essentially one line, it is probably better to copy code instead of falling through.

[atanasyan]

Address review comments: added blank lines, curly brackets, replaced LLVM_FALLTHROUGH by actual code.

[ruiu]

LGTM

ELF/Arch/Mips.cpp

RelExpr MIPS<ELFT>::getRelExpr(uint32_t Type, const SymbolBody &S,
                                const uint8_t *Loc) const {
   // See comment in the calculateMipsRelChain.
   if (ELFT::Is64Bits || Config->MipsN32Abi)
     Type &= 0xff;
   switch (Type) {
   default:
     return R_ABS;
   case R_MIPS_JALR:
+  case R_MICROMIPS_JALR:
     return R_HINT;
   case R_MIPS_GPREL16:
   case R_MIPS_GPREL32:
+  case R_MICROMIPS_GPREL16:
+  case R_MICROMIPS_GPREL7_S2:
     return R_MIPS_GOTREL;
   case R_MIPS_26:
     return R_PLT;
+  case R_MICROMIPS_26_S1:
+    return R_PLT;
+  case R_MICROMIPS_PC26_S1:
+    return R_PLT_PC;
   case R_MIPS_HI16:
   case R_MIPS_LO16:
+  case R_MICROMIPS_HI16:
+  case R_MICROMIPS_LO16:
     // R_MIPS_HI16/R_MIPS_LO16 relocations against _gp_disp calculate
     // offset between start of function and 'gp' value which by default
     // equal to the start of .got section. In that case we consider these
     // relocations as relative.
     if (&S == ElfSym::MipsGpDisp)
       return R_MIPS_GOT_GP_PC;
     if (&S == ElfSym::MipsLocalGp)
       return R_MIPS_GOT_GP;
     LLVM_FALLTHROUGH;
   case R_MIPS_GOT_OFST:
+  case R_MICROMIPS_GOT_OFST:
     return R_ABS;
   case R_MIPS_PC32:
   case R_MIPS_PC16:
   case R_MIPS_PC19_S2:
   case R_MIPS_PC21_S2:
   case R_MIPS_PC26_S2:
   case R_MIPS_PCHI16:
   case R_MIPS_PCLO16:
+  case R_MICROMIPS_PC7_S1:
+  case R_MICROMIPS_PC10_S1:
+  case R_MICROMIPS_PC16_S1:
+  case R_MICROMIPS_PC18_S3:
+  case R_MICROMIPS_PC19_S2:
+  case R_MICROMIPS_PC23_S2:
+  case R_MICROMIPS_PC21_S1:
     return R_PC;
   case R_MIPS_GOT16:
+  case R_MICROMIPS_GOT16:
     if (S.isLocal())
       return R_MIPS_GOT_LOCAL_PAGE;
     LLVM_FALLTHROUGH;
   case R_MIPS_CALL16:
   case R_MIPS_GOT_DISP:
   case R_MIPS_TLS_GOTTPREL:
+  case R_MICROMIPS_CALL16:
+  case R_MICROMIPS_GOT_DISP:
+  case R_MICROMIPS_TLS_GOTTPREL:
     return R_MIPS_GOT_OFF;
   case R_MIPS_CALL_HI16:
   case R_MIPS_CALL_LO16:
   case R_MIPS_GOT_HI16:
   case R_MIPS_GOT_LO16:
+  case R_MICROMIPS_CALL_HI16:
+  case R_MICROMIPS_CALL_LO16:
+  case R_MICROMIPS_GOT_HI16:
+  case R_MICROMIPS_GOT_LO16:
     return R_MIPS_GOT_OFF32;
   case R_MIPS_GOT_PAGE:
+  case R_MICROMIPS_GOT_PAGE:
     return R_MIPS_GOT_LOCAL_PAGE;
   case R_MIPS_TLS_GD:
+  case R_MICROMIPS_TLS_GD:
     return R_MIPS_TLSGD;
   case R_MIPS_TLS_LDM:
+  case R_MICROMIPS_TLS_LDM:
     return R_MIPS_TLSLD;
   }
 }
 
 template <class ELFT> bool MIPS<ELFT>::isPicRel(uint32_t Type) const {
   return Type == R_MIPS_32 || Type == R_MIPS_64;
 }
 
 template <class ELFT> uint32_t MIPS<ELFT>::getDynRel(uint32_t Type) const {
   return RelativeRel;
 }
 
 template <class ELFT>
 void MIPS<ELFT>::writeGotPlt(uint8_t *Buf, const SymbolBody &) const {
   write32<ELFT::TargetEndianness>(Buf, InX::Plt->getVA());
 }
 
+template <endianness E> static uint32_t readShuffle(const uint8_t *Loc) {
+  // The major opcode of a microMIPS instruction needs to appear
+  // in the first 16-bit word (lowest address) for efficient hardware
+  // decode so that it knows if the instruction is 16-bit or 32-bit
+  // as early as possible. To do so, little-endian binaries keep 16-bit
+  // words in a big-endian order. That is why we have to swap these
+  // words to get a correct value.
+  uint32_t V = read32<E>(Loc);
+  if (E == support::little)
+    return (V << 16) | (V >> 16);
+  return V;
+}
+
 template <endianness E>
 static void writeRelocation(uint8_t *Loc, uint64_t V, uint8_t BitsSize,
                             uint8_t Shift) {
   uint32_t Instr = read32<E>(Loc);
   uint32_t Mask = 0xffffffff >> (32 - BitsSize);
   uint32_t Data = (Instr & ~Mask) | ((V >> Shift) & Mask);
   write32<E>(Loc, Data);
 }
 
+template <endianness E>
+static void writeMicroRelocation32(uint8_t *Loc, uint64_t V, uint8_t BitsSize,
+                                   uint8_t Shift) {
+  // See comments in readShuffle for purpose of this code.
+  uint16_t *Words = (uint16_t *)Loc;
+  if (E == support::little)
+    std::swap(Words[0], Words[1]);
+
+  writeRelocation<E>(Loc, V, BitsSize, Shift);
+
+  if (E == support::little)
+    std::swap(Words[0], Words[1]);
+}
+
+template <endianness E>
+static void writeMicroRelocation16(uint8_t *Loc, uint64_t V, uint8_t BitsSize,
+                                   uint8_t Shift) {
+  uint16_t Instr = read16<E>(Loc);
+  uint16_t Mask = 0xffff >> (16 - BitsSize);
+  uint16_t Data = (Instr & ~Mask) | ((V >> Shift) & Mask);
+  write16<E>(Loc, Data);
+}
+
+template <class ELFT> static bool isMicroMips() {
+  // FIXME (simon): This code does not support the case when both
+  // microMIPS and MIPS object files are linked together.
+  const auto &FirstObj = cast<ELFFileBase<ELFT>>(*Config->FirstElf);
+  uint32_t Arch = FirstObj.getObj().getHeader()->e_flags & EF_MIPS_ARCH_ASE;
+  return Arch == EF_MIPS_MICROMIPS;
+}
+
 template <class ELFT> static bool isMipsR6() {
   const auto &FirstObj = cast<ELFFileBase<ELFT>>(*Config->FirstElf);
   uint32_t Arch = FirstObj.getObj().getHeader()->e_flags & EF_MIPS_ARCH;
   return Arch == EF_MIPS_ARCH_32R6 || Arch == EF_MIPS_ARCH_64R6;
 }
 
 template <class ELFT> void MIPS<ELFT>::writePltHeader(uint8_t *Buf) const {
   const endianness E = ELFT::TargetEndianness;
+  if (isMicroMips<ELFT>()) {
+    uint64_t GotPlt = In<ELFT>::GotPlt->getVA();
+    uint64_t Plt = In<ELFT>::Plt->getVA();
+    // Overwrite trap instructions written by Writer::writeTrapInstr.
+    memset(Buf, 0, PltHeaderSize);
+
+    write16<E>(Buf, isMipsR6<ELFT>() ? 0x7860 : 0x7980);
+                                    // addiupc v1, (GOTPLT) - .
+    write16<E>(Buf + 4, 0xff23);    // lw      $25, 0($3)
+    write16<E>(Buf + 8, 0x0535);    // subu16  $2,  $2, $3
+    write16<E>(Buf + 10, 0x2525);   // srl16   $2,  $2, 2
+    write16<E>(Buf + 12, 0x3302);   // addiu   $24, $2, -2
+    write16<E>(Buf + 14, 0xfffe);
+    write16<E>(Buf + 16, 0x0dff);   // move    $15, $31
+    if (isMipsR6<ELFT>()) {
+      write16<E>(Buf + 18, 0x0f83); // move    $28, $3
+      write16<E>(Buf + 20, 0x472b); // jalrc   $25
+      write16<E>(Buf + 22, 0x0c00); // nop
+      relocateOne(Buf, R_MICROMIPS_PC19_S2, GotPlt - Plt);
+    } else {
+      write16<E>(Buf + 18, 0x45f9); // jalrc   $25
+      write16<E>(Buf + 20, 0x0f83); // move    $28, $3
+      write16<E>(Buf + 22, 0x0c00); // nop
+      relocateOne(Buf, R_MICROMIPS_PC23_S2, GotPlt - Plt);
+    }
+    return;
+  }
+
   if (Config->MipsN32Abi) {
     write32<E>(Buf, 0x3c0e0000);      // lui   $14, %hi(&GOTPLT[0])
     write32<E>(Buf + 4, 0x8dd90000);  // lw    $25, %lo(&GOTPLT[0])($14)
     write32<E>(Buf + 8, 0x25ce0000);  // addiu $14, $14, %lo(&GOTPLT[0])
     write32<E>(Buf + 12, 0x030ec023); // subu  $24, $24, $14
   } else {
     write32<E>(Buf, 0x3c1c0000);      // lui   $28, %hi(&GOTPLT[0])
     write32<E>(Buf + 4, 0x8f990000);  // lw    $25, %lo(&GOTPLT[0])($28)
template <class ELFT> void MIPS<ELFT>::writePltHeader(uint8_t *Buf) const {
   writeRelocation<E>(Buf + 8, GotPlt, 16, 0);
 }
 
 template <class ELFT>
 void MIPS<ELFT>::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
                           uint64_t PltEntryAddr, int32_t Index,
                           unsigned RelOff) const {
   const endianness E = ELFT::TargetEndianness;
+  if (isMicroMips<ELFT>()) {
+    // Overwrite trap instructions written by Writer::writeTrapInstr.
+    memset(Buf, 0, PltEntrySize);
+
+    if (isMipsR6<ELFT>()) {
+      write16<E>(Buf, 0x7840);      // addiupc $2, (GOTPLT) - .
+      write16<E>(Buf + 4, 0xff22);  // lw $25, 0($2)
+      write16<E>(Buf + 8, 0x0f02);  // move $24, $2
+      write16<E>(Buf + 10, 0x4723); // jrc $25 / jr16 $25
+      relocateOne(Buf, R_MICROMIPS_PC19_S2, GotPltEntryAddr - PltEntryAddr);
+    } else {
+      write16<E>(Buf, 0x7900);      // addiupc $2, (GOTPLT) - .
+      write16<E>(Buf + 4, 0xff22);  // lw $25, 0($2)
+      write16<E>(Buf + 8, 0x4599);  // jrc $25 / jr16 $25
+      write16<E>(Buf + 10, 0x0f02); // move $24, $2
+      relocateOne(Buf, R_MICROMIPS_PC23_S2, GotPltEntryAddr - PltEntryAddr);
+    }
+    return;
+  }
+
   write32<E>(Buf, 0x3c0f0000);     // lui   $15, %hi(.got.plt entry)
   write32<E>(Buf + 4, 0x8df90000); // l[wd] $25, %lo(.got.plt entry)($15)
                                    // jr    $25
   write32<E>(Buf + 8, isMipsR6<ELFT>() ? 0x03200009 : 0x03200008);
   write32<E>(Buf + 12, 0x25f80000); // addiu $24, $15, %lo(.got.plt entry)
   writeRelocation<E>(Buf, GotPltEntryAddr + 0x8000, 16, 16);
   writeRelocation<E>(Buf + 4, GotPltEntryAddr, 16, 0);
   writeRelocation<E>(Buf + 12, GotPltEntryAddr, 16, 0);
 }
 
 template <class ELFT>
 bool MIPS<ELFT>::needsThunk(RelExpr Expr, uint32_t Type, const InputFile *File,
                             const SymbolBody &S) const {
   // Any MIPS PIC code function is invoked with its address in register $t9.
   // So if we have a branch instruction from non-PIC code to the PIC one
   // we cannot make the jump directly and need to create a small stubs
   // to save the target function address.
   // See page 3-38 ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
-  if (Type != R_MIPS_26)
+  if (Type != R_MIPS_26 && Type != R_MICROMIPS_26_S1 &&
+      Type != R_MICROMIPS_PC26_S1)
     return false;
   auto *F = dyn_cast_or_null<ELFFileBase<ELFT>>(File);
   if (!F)
     return false;
   // If current file has PIC code, LA25 stub is not required.
   if (F->getObj().getHeader()->e_flags & EF_MIPS_PIC)
     return false;
   auto *D = dyn_cast<DefinedRegular>(&S);
int64_t MIPS<ELFT>::getImplicitAddend(const uint8_t *Buf, uint32_t Type) const {
   case R_MIPS_GPREL16:
   case R_MIPS_LO16:
   case R_MIPS_PCLO16:
   case R_MIPS_TLS_DTPREL_HI16:
   case R_MIPS_TLS_DTPREL_LO16:
   case R_MIPS_TLS_TPREL_HI16:
   case R_MIPS_TLS_TPREL_LO16:
     return SignExtend64<16>(read32<E>(Buf));
+  case R_MICROMIPS_GOT16:
+  case R_MICROMIPS_HI16:
+    return SignExtend64<16>(readShuffle<E>(Buf)) << 16;
+  case R_MICROMIPS_GPREL16:
+  case R_MICROMIPS_LO16:
+  case R_MICROMIPS_TLS_DTPREL_HI16:
+  case R_MICROMIPS_TLS_DTPREL_LO16:
+  case R_MICROMIPS_TLS_TPREL_HI16:
+  case R_MICROMIPS_TLS_TPREL_LO16:
+    return SignExtend64<16>(readShuffle<E>(Buf));
+  case R_MICROMIPS_GPREL7_S2:
+    return SignExtend64<9>(readShuffle<E>(Buf) << 2);
   case R_MIPS_PC16:
     return SignExtend64<18>(read32<E>(Buf) << 2);
   case R_MIPS_PC19_S2:
     return SignExtend64<21>(read32<E>(Buf) << 2);
   case R_MIPS_PC21_S2:
     return SignExtend64<23>(read32<E>(Buf) << 2);
   case R_MIPS_PC26_S2:
     return SignExtend64<28>(read32<E>(Buf) << 2);
   case R_MIPS_PC32:
     return SignExtend64<32>(read32<E>(Buf));
+  case R_MICROMIPS_26_S1:
+    return SignExtend64<27>(readShuffle<E>(Buf) << 1);
+  case R_MICROMIPS_PC7_S1:
+    return SignExtend64<8>(read16<E>(Buf) << 1);
+  case R_MICROMIPS_PC10_S1:
+    return SignExtend64<11>(read16<E>(Buf) << 1);
+  case R_MICROMIPS_PC16_S1:
+    return SignExtend64<17>(readShuffle<E>(Buf) << 1);
+  case R_MICROMIPS_PC18_S3:
+    return SignExtend64<21>(readShuffle<E>(Buf) << 3);
+  case R_MICROMIPS_PC19_S2:
+    return SignExtend64<21>(readShuffle<E>(Buf) << 2);
+  case R_MICROMIPS_PC21_S1:
+    return SignExtend64<22>(readShuffle<E>(Buf) << 1);
+  case R_MICROMIPS_PC23_S2:
+    return SignExtend64<25>(readShuffle<E>(Buf) << 2);
+  case R_MICROMIPS_PC26_S1:
+    return SignExtend64<27>(readShuffle<E>(Buf) << 1);
   }
 }
 
 static std::pair<uint32_t, uint64_t>
 calculateMipsRelChain(uint8_t *Loc, uint32_t Type, uint64_t Val) {
   // MIPS N64 ABI packs multiple relocations into the single relocation
   // record. In general, all up to three relocations can have arbitrary
   // types. In fact, Clang and GCC uses only a few combinations. For now,
calculateMipsRelChain(uint8_t *Loc, uint32_t Type, uint64_t Val) {
   uint32_t Type2 = (Type >> 8) & 0xff;
   uint32_t Type3 = (Type >> 16) & 0xff;
   if (Type2 == R_MIPS_NONE && Type3 == R_MIPS_NONE)
     return std::make_pair(Type, Val);
   if (Type2 == R_MIPS_64 && Type3 == R_MIPS_NONE)
     return std::make_pair(Type2, Val);
   if (Type2 == R_MIPS_SUB && (Type3 == R_MIPS_HI16 || Type3 == R_MIPS_LO16))
     return std::make_pair(Type3, -Val);
+  if (Type2 == R_MICROMIPS_SUB &&
+      (Type3 == R_MICROMIPS_HI16 || Type3 == R_MICROMIPS_LO16))
+    return std::make_pair(Type3, -Val);
   error(getErrorLocation(Loc) + "unsupported relocations combination " +
         Twine(Type));
   return std::make_pair(Type & 0xff, Val);
 }
 
 template <class ELFT>
 void MIPS<ELFT>::relocateOne(uint8_t *Loc, uint32_t Type, uint64_t Val) const {
   const endianness E = ELFT::TargetEndianness;
   // Thread pointer and DRP offsets from the start of TLS data area.
   // https://www.linux-mips.org/wiki/NPTL
   if (Type == R_MIPS_TLS_DTPREL_HI16 || Type == R_MIPS_TLS_DTPREL_LO16 ||
-      Type == R_MIPS_TLS_DTPREL32 || Type == R_MIPS_TLS_DTPREL64)
+      Type == R_MIPS_TLS_DTPREL32 || Type == R_MIPS_TLS_DTPREL64 ||
+      Type == R_MICROMIPS_TLS_DTPREL_HI16 ||
+      Type == R_MICROMIPS_TLS_DTPREL_LO16)
     Val -= 0x8000;
   else if (Type == R_MIPS_TLS_TPREL_HI16 || Type == R_MIPS_TLS_TPREL_LO16 ||
-           Type == R_MIPS_TLS_TPREL32 || Type == R_MIPS_TLS_TPREL64)
+           Type == R_MIPS_TLS_TPREL32 || Type == R_MIPS_TLS_TPREL64 ||
+           Type == R_MICROMIPS_TLS_TPREL_HI16 ||
+           Type == R_MICROMIPS_TLS_TPREL_LO16)
     Val -= 0x7000;
   if (ELFT::Is64Bits || Config->MipsN32Abi)
     std::tie(Type, Val) = calculateMipsRelChain(Loc, Type, Val);
   switch (Type) {
   case R_MIPS_32:
   case R_MIPS_GPREL32:
   case R_MIPS_TLS_DTPREL32:
   case R_MIPS_TLS_TPREL32:
case R_MIPS_GOT16:
     // to store a correct addend value.
     if (Config->Relocatable) {
       writeRelocation<E>(Loc, Val + 0x8000, 16, 16);
     } else {
       checkInt<16>(Loc, Val, Type);
       writeRelocation<E>(Loc, Val, 16, 0);
     }
     break;
+  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_GOT_DISP:
   case R_MIPS_GOT_PAGE:
   case R_MIPS_GPREL16:
   case R_MIPS_TLS_GD:
   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:
+    checkInt<16>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 16, 0);
+    break;
+  case R_MICROMIPS_CALL16:
+  case R_MICROMIPS_CALL_LO16:
+  case R_MICROMIPS_GOT_OFST:
+  case R_MICROMIPS_LO16:
+  case R_MICROMIPS_TLS_DTPREL_LO16:
+  case R_MICROMIPS_TLS_GOTTPREL:
+  case R_MICROMIPS_TLS_TPREL_LO16:
+    writeMicroRelocation32<E>(Loc, Val, 16, 0);
+    break;
+  case R_MICROMIPS_GPREL7_S2:
+    checkInt<7>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 7, 2);
+    break;
   case R_MIPS_CALL_HI16:
   case R_MIPS_GOT_HI16:
   case R_MIPS_HI16:
   case R_MIPS_PCHI16:
   case R_MIPS_TLS_DTPREL_HI16:
   case R_MIPS_TLS_TPREL_HI16:
     writeRelocation<E>(Loc, Val + 0x8000, 16, 16);
     break;
+  case R_MICROMIPS_CALL_HI16:
+  case R_MICROMIPS_GOT_HI16:
+  case R_MICROMIPS_HI16:
+  case R_MICROMIPS_TLS_DTPREL_HI16:
+  case R_MICROMIPS_TLS_TPREL_HI16:
+    writeMicroRelocation32<E>(Loc, Val + 0x8000, 16, 16);
+    break;
   case R_MIPS_HIGHER:
     writeRelocation<E>(Loc, Val + 0x80008000, 16, 32);
     break;
   case R_MIPS_HIGHEST:
     writeRelocation<E>(Loc, Val + 0x800080008000, 16, 48);
     break;
+  case R_MICROMIPS_HIGHER:
+    writeMicroRelocation32<E>(Loc, Val + 0x80008000, 16, 32);
+    break;
+  case R_MICROMIPS_HIGHEST:
+    writeMicroRelocation32<E>(Loc, Val + 0x800080008000, 16, 48);
+    break;
   case R_MIPS_JALR:
+  case R_MICROMIPS_JALR:
     // Ignore this optimization relocation for now
     break;
   case R_MIPS_PC16:
     checkAlignment<4>(Loc, Val, Type);
     checkInt<18>(Loc, Val, Type);
     writeRelocation<E>(Loc, Val, 16, 2);
     break;
   case R_MIPS_PC19_S2:
void MIPS<ELFT>::relocateOne(uint8_t *Loc, uint32_t Type, uint64_t Val) const {
   case R_MIPS_PC26_S2:
     checkAlignment<4>(Loc, Val, Type);
     checkInt<28>(Loc, Val, Type);
     writeRelocation<E>(Loc, Val, 26, 2);
     break;
   case R_MIPS_PC32:
     writeRelocation<E>(Loc, Val, 32, 0);
     break;
+  case R_MICROMIPS_26_S1:
+  case R_MICROMIPS_PC26_S1:
+    checkInt<27>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 26, 1);
+    break;
+  case R_MICROMIPS_PC7_S1:
+    checkInt<8>(Loc, Val, Type);
+    writeMicroRelocation16<E>(Loc, Val, 7, 1);
+    break;
+  case R_MICROMIPS_PC10_S1:
+    checkInt<11>(Loc, Val, Type);
+    writeMicroRelocation16<E>(Loc, Val, 10, 1);
+    break;
+  case R_MICROMIPS_PC16_S1:
+    checkInt<17>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 16, 1);
+    break;
+  case R_MICROMIPS_PC18_S3:
+    checkInt<21>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 18, 3);
+    break;
+  case R_MICROMIPS_PC19_S2:
+    checkInt<21>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 19, 2);
+    break;
+  case R_MICROMIPS_PC21_S1:
+    checkInt<22>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 21, 1);
+    break;
+  case R_MICROMIPS_PC23_S2:
+    checkInt<25>(Loc, Val, Type);
+    writeMicroRelocation32<E>(Loc, Val, 23, 2);
+    break;
   default:
     error(getErrorLocation(Loc) + "unrecognized reloc " + Twine(Type));
   }
 }
 
 template <class ELFT>
 bool MIPS<ELFT>::usesOnlyLowPageBits(uint32_t Type) const {
-  return Type == R_MIPS_LO16 || Type == R_MIPS_GOT_OFST;
+  return Type == R_MIPS_LO16 || Type == R_MIPS_GOT_OFST ||
+         Type == R_MICROMIPS_LO16 || Type == R_MICROMIPS_GOT_OFST;
 }
 
 template <class ELFT> TargetInfo *elf::getMipsTargetInfo() {
   static MIPS<ELFT> Target;
   return &Target;
 }
 
 template TargetInfo *elf::getMipsTargetInfo<ELF32LE>();
 template TargetInfo *elf::getMipsTargetInfo<ELF32BE>();
 template TargetInfo *elf::getMipsTargetInfo<ELF64LE>();
 template TargetInfo *elf::getMipsTargetInfo<ELF64BE>();

ELF/InputSection.cpp

static uint64_t getRelocTargetVA(uint32_t Type, int64_t A, uint64_t P,
   case R_MIPS_GOT_GP:
     return InX::MipsGot->getGp() + A;
   case R_MIPS_GOT_GP_PC: {
     // R_MIPS_LO16 expression has R_MIPS_GOT_GP_PC type iif the target
     // is _gp_disp symbol. In that case we should use the following
     // formula for calculation "AHL + GP - P + 4". For details see p. 4-19 at
     // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
     uint64_t V = InX::MipsGot->getGp() + A - P;
-    if (Type == R_MIPS_LO16)
+    if (Type == R_MIPS_LO16 || Type == R_MICROMIPS_LO16)
       V += 4;
     return V;
   }
   case R_MIPS_GOT_LOCAL_PAGE:
     // If relocation against MIPS local symbol requires GOT entry, this entry
     // should be initialized by 'page address'. This address is high 16-bits
     // of sum the symbol's value and the addend.
     return InX::MipsGot->getVA() + InX::MipsGot->getPageEntryOffset(Body, A) -

ELF/Relocations.cpp

static bool isPreemptible(const SymbolBody &Body, uint32_t Type) {
   // for example, should not attempt to create a dynamic relocation even
   // if the target symbol is preemptible. There are two two MIPS GP-relative
   // relocations R_MIPS_GPREL16 and R_MIPS_GPREL32. But only R_MIPS_GPREL16
   // can be against a preemptible symbol.
   // To get MIPS relocation type we apply 0xff mask. In case of O32 ABI all
   // relocation types occupy eight bit. In case of N64 ABI we extract first
   // relocation from 3-in-1 packet because only the first relocation can
   // be against a real symbol.
-  if (Config->EMachine == EM_MIPS && (Type & 0xff) == R_MIPS_GPREL16)
+  if (Config->EMachine == EM_MIPS) {
+    Type &= 0xff;
+    if (Type == R_MIPS_GPREL16 || Type == R_MICROMIPS_GPREL16 ||
+        Type == R_MICROMIPS_GPREL7_S2)
       return false;
+  }
   return Body.isPreemptible();
 }
 
 // This function is similar to the `handleTlsRelocation`. MIPS does not
 // support any relaxations for TLS relocations so by factoring out MIPS
 // handling in to the separate function we can simplify the code and do not
 // pollute other `handleTlsRelocation` by MIPS `ifs` statements.
 // Mips has a custom MipsGotSection that handles the writing of GOT entries

 }
 
 static uint32_t getMipsPairType(uint32_t Type, const SymbolBody &Sym) {
   switch (Type) {
   case R_MIPS_HI16:
     return R_MIPS_LO16;
   case R_MIPS_GOT16:
     return Sym.isLocal() ? R_MIPS_LO16 : R_MIPS_NONE;
+  case R_MICROMIPS_GOT16:
+    return Sym.isLocal() ? R_MICROMIPS_LO16 : R_MIPS_NONE;
   case R_MIPS_PCHI16:
     return R_MIPS_PCLO16;
   case R_MICROMIPS_HI16:
     return R_MICROMIPS_LO16;
   default:
     return R_MIPS_NONE;
   }
 }

test/ELF/Inputs/mips-micro.s

+  .text
+  .set micromips
+  .global foo
+  .type foo,@function
+foo:
+  nop
+
+  .set nomicromips
+  .global bar
+  .type bar,@function
+bar:
+  nop

test/ELF/mips-micro-got.s

+# Check microMIPS GOT relocations for O32 ABI.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux -mattr=micromips \
+# RUN:         %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux -mattr=micromips \
+# RUN:         %S/Inputs/mips-dynamic.s -o %t2.o
+# RUN: ld.lld %t2.o -shared -o %t.so
+# RUN: ld.lld %t1.o %t.so -o %t.exe
+# RUN: llvm-readobj -mips-plt-got %t.exe | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK:      Local entries [
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32744
+# CHECK-NEXT:     Initial: 0x30000
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32740
+# CHECK-NEXT:     Initial: 0x40000
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+# CHECK-NEXT: Global entries [
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32736
+# CHECK-NEXT:     Initial: 0x0
+# CHECK-NEXT:     Value: 0x0
+# CHECK-NEXT:     Type: Function
+# CHECK-NEXT:     Section: Undefined
+# CHECK-NEXT:     Name: foo0
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+
+  .text
+  .global __start
+__start:
+  lw       $4, %got(data)($28)
+  addiu    $4, $4, %lo(data)
+  lw      $25, %call16(foo0)($28)
+
+  .data
+data:
+  .word 0

test/ELF/mips-micro-got64.s

+# Check microMIPS GOT relocations for N64 ABI.
+
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-linux -mattr=micromips \
+# RUN:         %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-linux -mattr=micromips \
+# RUN:         %S/Inputs/mips-dynamic.s -o %t2.o
+# RUN: ld.lld %t2.o -shared -o %t.so
+# RUN: ld.lld %t1.o %t.so -o %t.exe
+# RUN: llvm-readobj -mips-plt-got %t.exe | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK:      Local entries [
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32736
+# CHECK-NEXT:     Initial: 0x30000
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32728
+# CHECK-NEXT:     Initial: 0x40000
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+# CHECK-NEXT: Global entries [
+# CHECK-NEXT:   Entry {
+# CHECK-NEXT:     Address:
+# CHECK-NEXT:     Access: -32720
+# CHECK-NEXT:     Initial: 0x0
+# CHECK-NEXT:     Value: 0x0
+# CHECK-NEXT:     Type: Function
+# CHECK-NEXT:     Section: Undefined
+# CHECK-NEXT:     Name: foo0
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+
+  .text
+  .global __start
+__start:
+  lui     $28, %hi(%neg(%gp_rel(foo0)))
+  addiu   $28, $28, %lo(%neg(%gp_rel(foo0)))
+  lw       $4, %got_page(data)($28)
+  addiu    $4, $4, %got_ofst(data)
+  lw      $25, %call16(foo0)($28)
+
+  .data
+data:
+  .word 0

test/ELF/mips-micro-jal.s

+# Check PLT creation for microMIPS to microMIPS calls.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         -mattr=micromips %S/Inputs/mips-micro.s -o %t1eb.o
+# RUN: ld.lld -shared -o %teb.so %t1eb.o
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         -mattr=micromips %s -o %t2eb.o
+# RUN: ld.lld -o %teb.exe %t2eb.o %teb.so
+# RUN: llvm-objdump -d -mattr=micromips %teb.exe | FileCheck --check-prefix=EB %s
+# RUN: llvm-readobj -mips-plt-got %teb.exe | FileCheck --check-prefix=PLT %s
+
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux \
+# RUN:         -mattr=micromips %S/Inputs/mips-micro.s -o %t1el.o
+# RUN: ld.lld -shared -o %tel.so %t1el.o
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux \
+# RUN:         -mattr=micromips %s -o %t2el.o
+# RUN: ld.lld -o %tel.exe %t2el.o %tel.so
+# RUN: llvm-objdump -d -mattr=micromips %tel.exe | FileCheck --check-prefix=EL %s
+# RUN: llvm-readobj -mips-plt-got %tel.exe | FileCheck --check-prefix=PLT %s
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         -mattr=micromips -mcpu=mips32r6 %S/Inputs/mips-micro.s -o %t1eb.o
+# RUN: ld.lld -shared -o %teb.so %t1eb.o
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         -mattr=micromips -mcpu=mips32r6 %s -o %t2eb.o
+# RUN: ld.lld -o %teb.exe %t2eb.o %teb.so
+# RUN: llvm-objdump -d -mattr=micromips %teb.exe | FileCheck --check-prefix=EBR6 %s
+
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux \
+# RUN:         -mattr=micromips -mcpu=mips32r6 %S/Inputs/mips-micro.s -o %t1el.o
+# RUN: ld.lld -shared -o %tel.so %t1el.o
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux \
+# RUN:         -mattr=micromips -mcpu=mips32r6 %s -o %t2el.o
+# RUN: ld.lld -o %tel.exe %t2el.o %tel.so
+# RUN: llvm-objdump -d -mattr=micromips %tel.exe | FileCheck --check-prefix=ELR6 %s
+
+# REQUIRES: mips
+
+# EB:      Disassembly of section .plt:
+# EB-NEXT: .plt:
+# EB-NEXT:    20010:       79 80 3f fd     addiupc $3, 65524
+# EB-NEXT:    20014:       ff 23 00 00     lw      $25, 0($3)
+# EB-NEXT:    20018:       05 35           subu16  $2, $2, $3
+# EB-NEXT:    2001a:       25 25           srl16   $2, $2, 2
+# EB-NEXT:    2001c:       33 02 ff fe     addiu   $24, $2, -2
+# EB-NEXT:    20020:       0d ff           move    $15, $ra
+# EB-NEXT:    20022:       45 f9           jalrs16 $25
+# EB-NEXT:    20024:       0f 83           move    $gp, $3
+# EB-NEXT:    20026:       0c 00           nop
+# EB-NEXT:    20028:       00 00 00 00     nop
+# EB-NEXT:    2002c:       00 00 00 00     nop
+
+# EB-NEXT:    20030:       79 00 3f f7     addiupc $2, 65500
+# EB-NEXT:    20034:       ff 22 00 00     lw      $25, 0($2)
+# EB-NEXT:    20038:       45 99           jr16    $25
+# EB-NEXT:    2003a:       0f 02           move    $24, $2
+
+# EL:      Disassembly of section .plt:
+# EL-NEXT: .plt:
+# EL-NEXT:    20010:       80 79 fd 3f     addiupc $3, 65524
+# EL-NEXT:    20014:       23 ff 00 00     lw      $25, 0($3)
+# EL-NEXT:    20018:       35 05           subu16  $2, $2, $3
+# EL-NEXT:    2001a:       25 25           srl16   $2, $2, 2
+# EL-NEXT:    2001c:       02 33 fe ff     addiu   $24, $2, -2
+# EL-NEXT:    20020:       ff 0d           move    $15, $ra
+# EL-NEXT:    20022:       f9 45           jalrs16 $25
+# EL-NEXT:    20024:       83 0f           move    $gp, $3
+# EL-NEXT:    20026:       00 0c           nop
+# EL-NEXT:    20028:       00 00 00 00     nop
+# EL-NEXT:    2002c:       00 00 00 00     nop
+
+# EL-NEXT:    20030:       00 79 f7 3f     addiupc $2, 65500
+# EL-NEXT:    20034:       22 ff 00 00     lw      $25, 0($2)
+# EL-NEXT:    20038:       99 45           jr16    $25
+# EL-NEXT:    2003a:       02 0f           move    $24, $2
+
+# EBR6:      Disassembly of section .plt:
+# EBR6-NEXT: .plt:
+# EBR6-NEXT:    20010:       78 60 3f fd     addiupc $3, 65524
+# EBR6-NEXT:    20014:       ff 23 00 00     lw      $25, 0($3)
+# EBR6-NEXT:    20018:       05 35           subu16  $2, $2, $3
+# EBR6-NEXT:    2001a:       25 25           srl16   $2, $2, 2
+# EBR6-NEXT:    2001c:       33 02 ff fe     addiu   $24, $2, -2
+# EBR6-NEXT:    20020:       0d ff           move16  $15, $ra
+# EBR6-NEXT:    20022:       0f 83           move16  $gp, $3
+# EBR6-NEXT:    20024:       47 2b           jalr    $25
+
+# EBR6:         20030:       78 40 3f f7     addiupc $2, 65500
+# EBR6-NEXT:    20034:       ff 22 00 00     lw      $25, 0($2)
+# EBR6-NEXT:    20038:       0f 02           move16  $24, $2
+# EBR6-NEXT:    2003a:       47 23           jrc16   $25
+
+# ELR6:      Disassembly of section .plt:
+# ELR6-NEXT: .plt:
+# ELR6-NEXT:    20010:       60 78 fd 3f     addiupc $3, 65524
+# ELR6-NEXT:    20014:       23 ff 00 00     lw      $25, 0($3)
+# ELR6-NEXT:    20018:       35 05           subu16  $2, $2, $3
+# ELR6-NEXT:    2001a:       25 25           srl16   $2, $2, 2
+# ELR6-NEXT:    2001c:       02 33 fe ff     addiu   $24, $2, -2
+# ELR6-NEXT:    20020:       ff 0d           move16  $15, $ra
+# ELR6-NEXT:    20022:       83 0f           move16  $gp, $3
+# ELR6-NEXT:    20024:       2b 47           jalr    $25
+
+# ELR6:         20030:       40 78 f7 3f     addiupc $2, 65500
+# ELR6-NEXT:    20034:       22 ff 00 00     lw      $25, 0($2)
+# ELR6-NEXT:    20038:       02 0f           move16  $24, $2
+# ELR6-NEXT:    2003a:       23 47           jrc16   $25
+
+# PLT:      Entries [
+# PLT-NEXT:   Entry {
+# PLT-NEXT:     Address: 0x3000C
+#                        ^ 0x20030 + 65500
+# PLT-NEXT:     Initial:
+# PLT-NEXT:     Value: 0x0
+# PLT-NEXT:     Type: Function
+# PLT-NEXT:     Section: Undefined
+# PLT-NEXT:     Name: foo
+# PLT-NEXT:   }
+# PLT-NEXT: ]
+
+  .text
+  .set micromips
+  .global __start
+__start:
+  jal foo

test/ELF/mips-micro-relocs.s

+# Check handling of microMIPS relocations.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         -mattr=micromips %S/Inputs/mips-micro.s -o %t1eb.o
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux \
+# RUN:         -mattr=micromips %s -o %t2eb.o
+# RUN: ld.lld -o %teb.exe %t1eb.o %t2eb.o
+# RUN: llvm-objdump -d -t -mattr=micromips %teb.exe \
+# RUN:   | FileCheck --check-prefixes=EB,SYM %s
+
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux \
+# RUN:         -mattr=micromips %S/Inputs/mips-micro.s -o %t1el.o
+# RUN: llvm-mc -filetype=obj -triple=mipsel-unknown-linux \
+# RUN:         -mattr=micromips %s -o %t2el.o
+# RUN: ld.lld -o %tel.exe %t1el.o %t2el.o
+# RUN: llvm-objdump -d -t -mattr=micromips %tel.exe \
+# RUN:   | FileCheck --check-prefixes=EL,SYM %s
+
+# REQUIRES: mips
+
+# EB:      __start:
+# EB-NEXT:      20010:       41 a3 00 01     lui     $3, 1
+# EB-NEXT:      20014:       30 63 7f e0     addiu   $3, $3, 32736
+# EB-NEXT:      20018:       fc 7c 80 18     lw      $3, -32744($gp)
+# EB-NEXT:      2001c:       fc 63 80 18     lw      $3, -32744($3)
+# EB-NEXT:      20020:       8f 70           beqz16  $6, -32
+# EB-NEXT:      20022:       00 7e 00 00     sll     $3, $fp, 0
+# EB-NEXT:      20026:       cf ec           b16     -40
+# EB-NEXT:      20028:       00 00 00 00     nop
+# EB-NEXT:      2002c:       94 00 ff e8     b       -44
+
+# EL:      __start:
+# EL-NEXT:      20010:       a3 41 01 00     lui     $3, 1
+# EL-NEXT:      20014:       63 30 e0 7f     addiu   $3, $3, 32736
+# EL-NEXT:      20018:       7c fc 18 80     lw      $3, -32744($gp)
+# EL-NEXT:      2001c:       63 fc 18 80     lw      $3, -32744($3)
+# EL-NEXT:      20020:       70 8f           beqz16  $6, -32
+# EL-NEXT:      20022:       7e 00 00 00     sll     $3, $fp, 0
+# EL-NEXT:      20026:       ec cf           b16     -40
+# EL-NEXT:      20028:       00 00 00 00     nop
+# EL-NEXT:      2002c:       00 94 e8 ff     b       -44
+
+# SYM: 00037ff0         *ABS*           00000000 .hidden _gp
+# SYM: 00020000 g F     .text           00000000 foo
+# SYM: 00020010         .text           00000000 __start
+
+  .text
+  .set micromips
+  .global __start
+__start:
+  lui     $3, %hi(_gp_disp)       # R_MICROMIPS_HI16
+  addiu   $3, $3, %lo(_gp_disp)   # R_MICROMIPS_LO16
+
+  lw      $3, %call16(foo)($gp)   # R_MICROMIPS_CALL16
+  lw      $3, %got(foo)($3)       # R_MICROMIPS_GOT16
+
+  beqz16  $6, foo                 # R_MICROMIPS_PC7_S1
+  b16     foo                     # R_MICROMIPS_PC10_S1
+  b       foo                     # R_MICROMIPS_PC16_S1