1 //===-- RISCVAsmBackend.cpp - RISCV Assembler Backend ---------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #include "RISCVAsmBackend.h"
11 #include "RISCVMCExpr.h"
12 #include "llvm/ADT/APInt.h"
13 #include "llvm/MC/MCAssembler.h"
14 #include "llvm/MC/MCContext.h"
15 #include "llvm/MC/MCDirectives.h"
16 #include "llvm/MC/MCELFObjectWriter.h"
17 #include "llvm/MC/MCExpr.h"
18 #include "llvm/MC/MCObjectWriter.h"
19 #include "llvm/MC/MCSymbol.h"
20 #include "llvm/Support/ErrorHandling.h"
21 #include "llvm/Support/raw_ostream.h"
25 // If linker relaxation is enabled, or the relax option had previously been
26 // enabled, always emit relocations even if the fixup can be resolved. This is
27 // necessary for correctness as offsets may change during relaxation.
28 bool RISCVAsmBackend::shouldForceRelocation(const MCAssembler &Asm,
30 const MCValue &Target) {
31 bool ShouldForce = false;
33 switch ((unsigned)Fixup.getKind()) {
36 case RISCV::fixup_riscv_pcrel_lo12_i:
37 case RISCV::fixup_riscv_pcrel_lo12_s:
38 // For pcrel_lo12, force a relocation if the target of the corresponding
39 // pcrel_hi20 is not in the same fragment.
40 const MCFixup *T = cast<RISCVMCExpr>(Fixup.getValue())->getPCRelHiFixup();
42 Asm.getContext().reportError(Fixup.getLoc(),
43 "could not find corresponding %pcrel_hi");
47 switch ((unsigned)T->getKind()) {
49 llvm_unreachable("Unexpected fixup kind for pcrel_lo12");
51 case RISCV::fixup_riscv_pcrel_hi20:
52 ShouldForce = T->getValue()->findAssociatedFragment() !=
53 Fixup.getValue()->findAssociatedFragment();
59 return ShouldForce || STI.getFeatureBits()[RISCV::FeatureRelax] ||
63 bool RISCVAsmBackend::fixupNeedsRelaxationAdvanced(const MCFixup &Fixup,
66 const MCRelaxableFragment *DF,
67 const MCAsmLayout &Layout,
68 const bool WasForced) const {
69 // Return true if the symbol is actually unresolved.
70 // Resolved could be always false when shouldForceRelocation return true.
71 // We use !WasForced to indicate that the symbol is unresolved and not forced
72 // by shouldForceRelocation.
73 if (!Resolved && !WasForced)
76 int64_t Offset = int64_t(Value);
77 switch ((unsigned)Fixup.getKind()) {
80 case RISCV::fixup_riscv_rvc_branch:
81 // For compressed branch instructions the immediate must be
82 // in the range [-256, 254].
83 return Offset > 254 || Offset < -256;
84 case RISCV::fixup_riscv_rvc_jump:
85 // For compressed jump instructions the immediate must be
86 // in the range [-2048, 2046].
87 return Offset > 2046 || Offset < -2048;
91 void RISCVAsmBackend::relaxInstruction(const MCInst &Inst,
92 const MCSubtargetInfo &STI,
94 // TODO: replace this with call to auto generated uncompressinstr() function.
95 switch (Inst.getOpcode()) {
97 llvm_unreachable("Opcode not expected!");
99 // c.beqz $rs1, $imm -> beq $rs1, X0, $imm.
100 Res.setOpcode(RISCV::BEQ);
101 Res.addOperand(Inst.getOperand(0));
102 Res.addOperand(MCOperand::createReg(RISCV::X0));
103 Res.addOperand(Inst.getOperand(1));
106 // c.bnez $rs1, $imm -> bne $rs1, X0, $imm.
107 Res.setOpcode(RISCV::BNE);
108 Res.addOperand(Inst.getOperand(0));
109 Res.addOperand(MCOperand::createReg(RISCV::X0));
110 Res.addOperand(Inst.getOperand(1));
113 // c.j $imm -> jal X0, $imm.
114 Res.setOpcode(RISCV::JAL);
115 Res.addOperand(MCOperand::createReg(RISCV::X0));
116 Res.addOperand(Inst.getOperand(0));
119 // c.jal $imm -> jal X1, $imm.
120 Res.setOpcode(RISCV::JAL);
121 Res.addOperand(MCOperand::createReg(RISCV::X1));
122 Res.addOperand(Inst.getOperand(0));
127 // Given a compressed control flow instruction this function returns
128 // the expanded instruction.
129 unsigned RISCVAsmBackend::getRelaxedOpcode(unsigned Op) const {
138 case RISCV::C_JAL: // fall through.
143 bool RISCVAsmBackend::mayNeedRelaxation(const MCInst &Inst,
144 const MCSubtargetInfo &STI) const {
145 return getRelaxedOpcode(Inst.getOpcode()) != Inst.getOpcode();
148 bool RISCVAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
149 bool HasStdExtC = STI.getFeatureBits()[RISCV::FeatureStdExtC];
150 unsigned MinNopLen = HasStdExtC ? 2 : 4;
152 if ((Count % MinNopLen) != 0)
155 // The canonical nop on RISC-V is addi x0, x0, 0.
156 uint64_t Nop32Count = Count / 4;
157 for (uint64_t i = Nop32Count; i != 0; --i)
158 OS.write("\x13\0\0\0", 4);
160 // The canonical nop on RVC is c.nop.
162 uint64_t Nop16Count = (Count - Nop32Count * 4) / 2;
163 for (uint64_t i = Nop16Count; i != 0; --i)
164 OS.write("\x01\0", 2);
170 static uint64_t adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
172 unsigned Kind = Fixup.getKind();
175 llvm_unreachable("Unknown fixup kind!");
181 case RISCV::fixup_riscv_lo12_i:
182 case RISCV::fixup_riscv_pcrel_lo12_i:
183 return Value & 0xfff;
184 case RISCV::fixup_riscv_lo12_s:
185 case RISCV::fixup_riscv_pcrel_lo12_s:
186 return (((Value >> 5) & 0x7f) << 25) | ((Value & 0x1f) << 7);
187 case RISCV::fixup_riscv_hi20:
188 case RISCV::fixup_riscv_pcrel_hi20:
189 // Add 1 if bit 11 is 1, to compensate for low 12 bits being negative.
190 return ((Value + 0x800) >> 12) & 0xfffff;
191 case RISCV::fixup_riscv_jal: {
192 if (!isInt<21>(Value))
193 Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
195 Ctx.reportError(Fixup.getLoc(), "fixup value must be 2-byte aligned");
196 // Need to produce imm[19|10:1|11|19:12] from the 21-bit Value.
197 unsigned Sbit = (Value >> 20) & 0x1;
198 unsigned Hi8 = (Value >> 12) & 0xff;
199 unsigned Mid1 = (Value >> 11) & 0x1;
200 unsigned Lo10 = (Value >> 1) & 0x3ff;
202 // Inst{30-21} = Lo10;
204 // Inst{19-12} = Hi8;
205 Value = (Sbit << 19) | (Lo10 << 9) | (Mid1 << 8) | Hi8;
208 case RISCV::fixup_riscv_branch: {
209 if (!isInt<13>(Value))
210 Ctx.reportError(Fixup.getLoc(), "fixup value out of range");
212 Ctx.reportError(Fixup.getLoc(), "fixup value must be 2-byte aligned");
213 // Need to extract imm[12], imm[10:5], imm[4:1], imm[11] from the 13-bit
215 unsigned Sbit = (Value >> 12) & 0x1;
216 unsigned Hi1 = (Value >> 11) & 0x1;
217 unsigned Mid6 = (Value >> 5) & 0x3f;
218 unsigned Lo4 = (Value >> 1) & 0xf;
220 // Inst{30-25} = Mid6;
223 Value = (Sbit << 31) | (Mid6 << 25) | (Lo4 << 8) | (Hi1 << 7);
226 case RISCV::fixup_riscv_call: {
227 // Jalr will add UpperImm with the sign-extended 12-bit LowerImm,
228 // we need to add 0x800ULL before extract upper bits to reflect the
229 // effect of the sign extension.
230 uint64_t UpperImm = (Value + 0x800ULL) & 0xfffff000ULL;
231 uint64_t LowerImm = Value & 0xfffULL;
232 return UpperImm | ((LowerImm << 20) << 32);
234 case RISCV::fixup_riscv_rvc_jump: {
235 // Need to produce offset[11|4|9:8|10|6|7|3:1|5] from the 11-bit Value.
236 unsigned Bit11 = (Value >> 11) & 0x1;
237 unsigned Bit4 = (Value >> 4) & 0x1;
238 unsigned Bit9_8 = (Value >> 8) & 0x3;
239 unsigned Bit10 = (Value >> 10) & 0x1;
240 unsigned Bit6 = (Value >> 6) & 0x1;
241 unsigned Bit7 = (Value >> 7) & 0x1;
242 unsigned Bit3_1 = (Value >> 1) & 0x7;
243 unsigned Bit5 = (Value >> 5) & 0x1;
244 Value = (Bit11 << 10) | (Bit4 << 9) | (Bit9_8 << 7) | (Bit10 << 6) |
245 (Bit6 << 5) | (Bit7 << 4) | (Bit3_1 << 1) | Bit5;
248 case RISCV::fixup_riscv_rvc_branch: {
249 // Need to produce offset[8|4:3], [reg 3 bit], offset[7:6|2:1|5]
250 unsigned Bit8 = (Value >> 8) & 0x1;
251 unsigned Bit7_6 = (Value >> 6) & 0x3;
252 unsigned Bit5 = (Value >> 5) & 0x1;
253 unsigned Bit4_3 = (Value >> 3) & 0x3;
254 unsigned Bit2_1 = (Value >> 1) & 0x3;
255 Value = (Bit8 << 12) | (Bit4_3 << 10) | (Bit7_6 << 5) | (Bit2_1 << 3) |
263 void RISCVAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
264 const MCValue &Target,
265 MutableArrayRef<char> Data, uint64_t Value,
267 const MCSubtargetInfo *STI) const {
268 MCContext &Ctx = Asm.getContext();
269 MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind());
271 return; // Doesn't change encoding.
272 // Apply any target-specific value adjustments.
273 Value = adjustFixupValue(Fixup, Value, Ctx);
275 // Shift the value into position.
276 Value <<= Info.TargetOffset;
278 unsigned Offset = Fixup.getOffset();
279 unsigned NumBytes = alignTo(Info.TargetSize + Info.TargetOffset, 8) / 8;
281 assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!");
283 // For each byte of the fragment that the fixup touches, mask in the
284 // bits from the fixup value.
285 for (unsigned i = 0; i != NumBytes; ++i) {
286 Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff);
290 std::unique_ptr<MCObjectTargetWriter>
291 RISCVAsmBackend::createObjectTargetWriter() const {
292 return createRISCVELFObjectWriter(OSABI, Is64Bit);
295 MCAsmBackend *llvm::createRISCVAsmBackend(const Target &T,
296 const MCSubtargetInfo &STI,
297 const MCRegisterInfo &MRI,
298 const MCTargetOptions &Options) {
299 const Triple &TT = STI.getTargetTriple();
300 uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS());
301 return new RISCVAsmBackend(STI, OSABI, TT.isArch64Bit());