| //===-- RISCVAsmBackend.cpp - RISCV Assembler Backend ---------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "RISCVAsmBackend.h" |
| #include "RISCVMCExpr.h" |
| #include "llvm/ADT/APInt.h" |
| #include "llvm/MC/MCAsmLayout.h" |
| #include "llvm/MC/MCAssembler.h" |
| #include "llvm/MC/MCContext.h" |
| #include "llvm/MC/MCDirectives.h" |
| #include "llvm/MC/MCELFObjectWriter.h" |
| #include "llvm/MC/MCExpr.h" |
| #include "llvm/MC/MCObjectWriter.h" |
| #include "llvm/MC/MCSymbol.h" |
| #include "llvm/MC/MCValue.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/raw_ostream.h" |
| |
| using namespace llvm; |
| |
| // If linker relaxation is enabled, or the relax option had previously been |
| // enabled, always emit relocations even if the fixup can be resolved. This is |
| // necessary for correctness as offsets may change during relaxation. |
| bool RISCVAsmBackend::shouldForceRelocation(const MCAssembler &Asm, |
| const MCFixup &Fixup, |
| const MCValue &Target) { |
| switch (Fixup.getTargetKind()) { |
| default: |
| break; |
| case FK_Data_1: |
| case FK_Data_2: |
| case FK_Data_4: |
| case FK_Data_8: |
| if (Target.isAbsolute()) |
| return false; |
| break; |
| case RISCV::fixup_riscv_got_hi20: |
| case RISCV::fixup_riscv_tls_got_hi20: |
| case RISCV::fixup_riscv_tls_gd_hi20: |
| return true; |
| } |
| |
| return STI.getFeatureBits()[RISCV::FeatureRelax] || ForceRelocs; |
| } |
| |
| bool RISCVAsmBackend::fixupNeedsRelaxationAdvanced(const MCFixup &Fixup, |
| bool Resolved, |
| uint64_t Value, |
| const MCRelaxableFragment *DF, |
| const MCAsmLayout &Layout, |
| const bool WasForced) const { |
| // Return true if the symbol is actually unresolved. |
| // Resolved could be always false when shouldForceRelocation return true. |
| // We use !WasForced to indicate that the symbol is unresolved and not forced |
| // by shouldForceRelocation. |
| if (!Resolved && !WasForced) |
| return true; |
| |
| int64_t Offset = int64_t(Value); |
| switch (Fixup.getTargetKind()) { |
| default: |
| return false; |
| case RISCV::fixup_riscv_rvc_branch: |
| // For compressed branch instructions the immediate must be |
| // in the range [-256, 254]. |
| return Offset > 254 || Offset < -256; |
| case RISCV::fixup_riscv_rvc_jump: |
| // For compressed jump instructions the immediate must be |
| // in the range [-2048, 2046]. |
| return Offset > 2046 || Offset < -2048; |
| } |
| } |
| |
| void RISCVAsmBackend::relaxInstruction(const MCInst &Inst, |
| const MCSubtargetInfo &STI, |
| MCInst &Res) const { |
| // TODO: replace this with call to auto generated uncompressinstr() function. |
| switch (Inst.getOpcode()) { |
| default: |
| llvm_unreachable("Opcode not expected!"); |
| case RISCV::C_BEQZ: |
| // c.beqz $rs1, $imm -> beq $rs1, X0, $imm. |
| Res.setOpcode(RISCV::BEQ); |
| Res.addOperand(Inst.getOperand(0)); |
| Res.addOperand(MCOperand::createReg(RISCV::X0)); |
| Res.addOperand(Inst.getOperand(1)); |
| break; |
| case RISCV::C_BNEZ: |
| // c.bnez $rs1, $imm -> bne $rs1, X0, $imm. |
| Res.setOpcode(RISCV::BNE); |
| Res.addOperand(Inst.getOperand(0)); |
| Res.addOperand(MCOperand::createReg(RISCV::X0)); |
| Res.addOperand(Inst.getOperand(1)); |
| break; |
| case RISCV::C_J: |
| // c.j $imm -> jal X0, $imm. |
| Res.setOpcode(RISCV::JAL); |
| Res.addOperand(MCOperand::createReg(RISCV::X0)); |
| Res.addOperand(Inst.getOperand(0)); |
| break; |
| case RISCV::C_JAL: |
| // c.jal $imm -> jal X1, $imm. |
| Res.setOpcode(RISCV::JAL); |
| Res.addOperand(MCOperand::createReg(RISCV::X1)); |
| Res.addOperand(Inst.getOperand(0)); |
| break; |
| } |
| } |
| |
| // Given a compressed control flow instruction this function returns |
| // the expanded instruction. |
| unsigned RISCVAsmBackend::getRelaxedOpcode(unsigned Op) const { |
| switch (Op) { |
| default: |
| return Op; |
| case RISCV::C_BEQZ: |
| return RISCV::BEQ; |
| case RISCV::C_BNEZ: |
| return RISCV::BNE; |
| case RISCV::C_J: |
| case RISCV::C_JAL: // fall through. |
| return RISCV::JAL; |
| } |
| } |
| |
| bool RISCVAsmBackend::mayNeedRelaxation(const MCInst &Inst, |
| const MCSubtargetInfo &STI) const { |
| return getRelaxedOpcode(Inst.getOpcode()) != Inst.getOpcode(); |
| } |
| |
| bool RISCVAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const { |
| bool HasStdExtC = STI.getFeatureBits()[RISCV::FeatureStdExtC]; |
| unsigned MinNopLen = HasStdExtC ? 2 : 4; |
| |
| if ((Count % MinNopLen) != 0) |
| return false; |
| |
| // The canonical nop on RISC-V is addi x0, x0, 0. |
| for (; Count >= 4; Count -= 4) |
| OS.write("\x13\0\0\0", 4); |
| |
| // The canonical nop on RVC is c.nop. |
| if (Count && HasStdExtC) |
| OS.write("\x01\0", 2); |
| |
| return true; |
| } |
| |
| static uint64_t adjustFixupValue(const MCFixup &Fixup, uint64_t Value, |
| MCContext &Ctx) { |
| switch (Fixup.getTargetKind()) { |
| default: |
| llvm_unreachable("Unknown fixup kind!"); |
| case RISCV::fixup_riscv_got_hi20: |
| case RISCV::fixup_riscv_tls_got_hi20: |
| case RISCV::fixup_riscv_tls_gd_hi20: |
| llvm_unreachable("Relocation should be unconditionally forced\n"); |
| case FK_Data_1: |
| case FK_Data_2: |
| case FK_Data_4: |
| case FK_Data_8: |
| case FK_Data_6b: |
| return Value; |
| case RISCV::fixup_riscv_lo12_i: |
| case RISCV::fixup_riscv_pcrel_lo12_i: |
| case RISCV::fixup_riscv_tprel_lo12_i: |
| return Value & 0xfff; |
| case RISCV::fixup_riscv_lo12_s: |
| case RISCV::fixup_riscv_pcrel_lo12_s: |
| case RISCV::fixup_riscv_tprel_lo12_s: |
| return (((Value >> 5) & 0x7f) << 25) | ((Value & 0x1f) << 7); |
| case RISCV::fixup_riscv_hi20: |
| case RISCV::fixup_riscv_pcrel_hi20: |
| case RISCV::fixup_riscv_tprel_hi20: |
| // Add 1 if bit 11 is 1, to compensate for low 12 bits being negative. |
| return ((Value + 0x800) >> 12) & 0xfffff; |
| case RISCV::fixup_riscv_jal: { |
| if (!isInt<21>(Value)) |
| Ctx.reportError(Fixup.getLoc(), "fixup value out of range"); |
| if (Value & 0x1) |
| Ctx.reportError(Fixup.getLoc(), "fixup value must be 2-byte aligned"); |
| // Need to produce imm[19|10:1|11|19:12] from the 21-bit Value. |
| unsigned Sbit = (Value >> 20) & 0x1; |
| unsigned Hi8 = (Value >> 12) & 0xff; |
| unsigned Mid1 = (Value >> 11) & 0x1; |
| unsigned Lo10 = (Value >> 1) & 0x3ff; |
| // Inst{31} = Sbit; |
| // Inst{30-21} = Lo10; |
| // Inst{20} = Mid1; |
| // Inst{19-12} = Hi8; |
| Value = (Sbit << 19) | (Lo10 << 9) | (Mid1 << 8) | Hi8; |
| return Value; |
| } |
| case RISCV::fixup_riscv_branch: { |
| if (!isInt<13>(Value)) |
| Ctx.reportError(Fixup.getLoc(), "fixup value out of range"); |
| if (Value & 0x1) |
| Ctx.reportError(Fixup.getLoc(), "fixup value must be 2-byte aligned"); |
| // Need to extract imm[12], imm[10:5], imm[4:1], imm[11] from the 13-bit |
| // Value. |
| unsigned Sbit = (Value >> 12) & 0x1; |
| unsigned Hi1 = (Value >> 11) & 0x1; |
| unsigned Mid6 = (Value >> 5) & 0x3f; |
| unsigned Lo4 = (Value >> 1) & 0xf; |
| // Inst{31} = Sbit; |
| // Inst{30-25} = Mid6; |
| // Inst{11-8} = Lo4; |
| // Inst{7} = Hi1; |
| Value = (Sbit << 31) | (Mid6 << 25) | (Lo4 << 8) | (Hi1 << 7); |
| return Value; |
| } |
| case RISCV::fixup_riscv_call: |
| case RISCV::fixup_riscv_call_plt: { |
| // Jalr will add UpperImm with the sign-extended 12-bit LowerImm, |
| // we need to add 0x800ULL before extract upper bits to reflect the |
| // effect of the sign extension. |
| uint64_t UpperImm = (Value + 0x800ULL) & 0xfffff000ULL; |
| uint64_t LowerImm = Value & 0xfffULL; |
| return UpperImm | ((LowerImm << 20) << 32); |
| } |
| case RISCV::fixup_riscv_rvc_jump: { |
| // Need to produce offset[11|4|9:8|10|6|7|3:1|5] from the 11-bit Value. |
| unsigned Bit11 = (Value >> 11) & 0x1; |
| unsigned Bit4 = (Value >> 4) & 0x1; |
| unsigned Bit9_8 = (Value >> 8) & 0x3; |
| unsigned Bit10 = (Value >> 10) & 0x1; |
| unsigned Bit6 = (Value >> 6) & 0x1; |
| unsigned Bit7 = (Value >> 7) & 0x1; |
| unsigned Bit3_1 = (Value >> 1) & 0x7; |
| unsigned Bit5 = (Value >> 5) & 0x1; |
| Value = (Bit11 << 10) | (Bit4 << 9) | (Bit9_8 << 7) | (Bit10 << 6) | |
| (Bit6 << 5) | (Bit7 << 4) | (Bit3_1 << 1) | Bit5; |
| return Value; |
| } |
| case RISCV::fixup_riscv_rvc_branch: { |
| // Need to produce offset[8|4:3], [reg 3 bit], offset[7:6|2:1|5] |
| unsigned Bit8 = (Value >> 8) & 0x1; |
| unsigned Bit7_6 = (Value >> 6) & 0x3; |
| unsigned Bit5 = (Value >> 5) & 0x1; |
| unsigned Bit4_3 = (Value >> 3) & 0x3; |
| unsigned Bit2_1 = (Value >> 1) & 0x3; |
| Value = (Bit8 << 12) | (Bit4_3 << 10) | (Bit7_6 << 5) | (Bit2_1 << 3) | |
| (Bit5 << 2); |
| return Value; |
| } |
| |
| } |
| } |
| |
| bool RISCVAsmBackend::evaluateTargetFixup( |
| const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFixup &Fixup, |
| const MCFragment *DF, const MCValue &Target, uint64_t &Value, |
| bool &WasForced) { |
| const MCFixup *AUIPCFixup; |
| const MCFragment *AUIPCDF; |
| MCValue AUIPCTarget; |
| switch (Fixup.getTargetKind()) { |
| default: |
| llvm_unreachable("Unexpected fixup kind!"); |
| case RISCV::fixup_riscv_pcrel_hi20: |
| AUIPCFixup = &Fixup; |
| AUIPCDF = DF; |
| AUIPCTarget = Target; |
| break; |
| case RISCV::fixup_riscv_pcrel_lo12_i: |
| case RISCV::fixup_riscv_pcrel_lo12_s: { |
| AUIPCFixup = cast<RISCVMCExpr>(Fixup.getValue())->getPCRelHiFixup(&AUIPCDF); |
| if (!AUIPCFixup) { |
| Asm.getContext().reportError(Fixup.getLoc(), |
| "could not find corresponding %pcrel_hi"); |
| return true; |
| } |
| |
| // MCAssembler::evaluateFixup will emit an error for this case when it sees |
| // the %pcrel_hi, so don't duplicate it when also seeing the %pcrel_lo. |
| const MCExpr *AUIPCExpr = AUIPCFixup->getValue(); |
| if (!AUIPCExpr->evaluateAsRelocatable(AUIPCTarget, &Layout, AUIPCFixup)) |
| return true; |
| break; |
| } |
| } |
| |
| if (!AUIPCTarget.getSymA() || AUIPCTarget.getSymB()) |
| return false; |
| |
| const MCSymbolRefExpr *A = AUIPCTarget.getSymA(); |
| const MCSymbol &SA = A->getSymbol(); |
| if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) |
| return false; |
| |
| auto *Writer = Asm.getWriterPtr(); |
| if (!Writer) |
| return false; |
| |
| bool IsResolved = Writer->isSymbolRefDifferenceFullyResolvedImpl( |
| Asm, SA, *AUIPCDF, false, true); |
| if (!IsResolved) |
| return false; |
| |
| Value = Layout.getSymbolOffset(SA) + AUIPCTarget.getConstant(); |
| Value -= Layout.getFragmentOffset(AUIPCDF) + AUIPCFixup->getOffset(); |
| |
| if (shouldForceRelocation(Asm, *AUIPCFixup, AUIPCTarget)) { |
| WasForced = true; |
| return false; |
| } |
| |
| return true; |
| } |
| |
| void RISCVAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, |
| const MCValue &Target, |
| MutableArrayRef<char> Data, uint64_t Value, |
| bool IsResolved, |
| const MCSubtargetInfo *STI) const { |
| MCContext &Ctx = Asm.getContext(); |
| MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind()); |
| if (!Value) |
| return; // Doesn't change encoding. |
| // Apply any target-specific value adjustments. |
| Value = adjustFixupValue(Fixup, Value, Ctx); |
| |
| // Shift the value into position. |
| Value <<= Info.TargetOffset; |
| |
| unsigned Offset = Fixup.getOffset(); |
| unsigned NumBytes = alignTo(Info.TargetSize + Info.TargetOffset, 8) / 8; |
| |
| assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!"); |
| |
| // For each byte of the fragment that the fixup touches, mask in the |
| // bits from the fixup value. |
| for (unsigned i = 0; i != NumBytes; ++i) { |
| Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff); |
| } |
| } |
| |
| // Linker relaxation may change code size. We have to insert Nops |
| // for .align directive when linker relaxation enabled. So then Linker |
| // could satisfy alignment by removing Nops. |
| // The function return the total Nops Size we need to insert. |
| bool RISCVAsmBackend::shouldInsertExtraNopBytesForCodeAlign( |
| const MCAlignFragment &AF, unsigned &Size) { |
| // Calculate Nops Size only when linker relaxation enabled. |
| if (!STI.getFeatureBits()[RISCV::FeatureRelax]) |
| return false; |
| |
| bool HasStdExtC = STI.getFeatureBits()[RISCV::FeatureStdExtC]; |
| unsigned MinNopLen = HasStdExtC ? 2 : 4; |
| |
| if (AF.getAlignment() <= MinNopLen) { |
| return false; |
| } else { |
| Size = AF.getAlignment() - MinNopLen; |
| return true; |
| } |
| } |
| |
| // We need to insert R_RISCV_ALIGN relocation type to indicate the |
| // position of Nops and the total bytes of the Nops have been inserted |
| // when linker relaxation enabled. |
| // The function insert fixup_riscv_align fixup which eventually will |
| // transfer to R_RISCV_ALIGN relocation type. |
| bool RISCVAsmBackend::shouldInsertFixupForCodeAlign(MCAssembler &Asm, |
| const MCAsmLayout &Layout, |
| MCAlignFragment &AF) { |
| // Insert the fixup only when linker relaxation enabled. |
| if (!STI.getFeatureBits()[RISCV::FeatureRelax]) |
| return false; |
| |
| // Calculate total Nops we need to insert. If there are none to insert |
| // then simply return. |
| unsigned Count; |
| if (!shouldInsertExtraNopBytesForCodeAlign(AF, Count) || (Count == 0)) |
| return false; |
| |
| MCContext &Ctx = Asm.getContext(); |
| const MCExpr *Dummy = MCConstantExpr::create(0, Ctx); |
| // Create fixup_riscv_align fixup. |
| MCFixup Fixup = |
| MCFixup::create(0, Dummy, MCFixupKind(RISCV::fixup_riscv_align), SMLoc()); |
| |
| uint64_t FixedValue = 0; |
| MCValue NopBytes = MCValue::get(Count); |
| |
| Asm.getWriter().recordRelocation(Asm, Layout, &AF, Fixup, NopBytes, |
| FixedValue); |
| |
| return true; |
| } |
| |
| std::unique_ptr<MCObjectTargetWriter> |
| RISCVAsmBackend::createObjectTargetWriter() const { |
| return createRISCVELFObjectWriter(OSABI, Is64Bit); |
| } |
| |
| MCAsmBackend *llvm::createRISCVAsmBackend(const Target &T, |
| const MCSubtargetInfo &STI, |
| const MCRegisterInfo &MRI, |
| const MCTargetOptions &Options) { |
| const Triple &TT = STI.getTargetTriple(); |
| uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS()); |
| return new RISCVAsmBackend(STI, OSABI, TT.isArch64Bit(), Options); |
| } |