1 //===----- x86_64.cpp - Generic JITLink x86-64 edge kinds, utilities ------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // Generic utilities for graphs representing x86-64 objects. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/ExecutionEngine/JITLink/x86_64.h" 14 15 #define DEBUG_TYPE "jitlink" 16 17 namespace llvm { 18 namespace jitlink { 19 namespace x86_64 { 20 21 const char *getEdgeKindName(Edge::Kind K) { 22 switch (K) { 23 case Pointer64: 24 return "Pointer64"; 25 case Pointer32: 26 return "Pointer32"; 27 case Pointer32Signed: 28 return "Pointer32Signed"; 29 case Pointer16: 30 return "Pointer16"; 31 case Pointer8: 32 return "Pointer8"; 33 case Delta64: 34 return "Delta64"; 35 case Delta32: 36 return "Delta32"; 37 case Delta8: 38 return "Delta8"; 39 case NegDelta64: 40 return "NegDelta64"; 41 case NegDelta32: 42 return "NegDelta32"; 43 case Delta64FromGOT: 44 return "Delta64FromGOT"; 45 case PCRel32: 46 return "PCRel32"; 47 case BranchPCRel32: 48 return "BranchPCRel32"; 49 case BranchPCRel32ToPtrJumpStub: 50 return "BranchPCRel32ToPtrJumpStub"; 51 case BranchPCRel32ToPtrJumpStubBypassable: 52 return "BranchPCRel32ToPtrJumpStubBypassable"; 53 case RequestGOTAndTransformToDelta32: 54 return "RequestGOTAndTransformToDelta32"; 55 case RequestGOTAndTransformToDelta64: 56 return "RequestGOTAndTransformToDelta64"; 57 case RequestGOTAndTransformToDelta64FromGOT: 58 return "RequestGOTAndTransformToDelta64FromGOT"; 59 case PCRel32GOTLoadREXRelaxable: 60 return "PCRel32GOTLoadREXRelaxable"; 61 case RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable: 62 return "RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable"; 63 case PCRel32GOTLoadRelaxable: 64 return "PCRel32GOTLoadRelaxable"; 65 case RequestGOTAndTransformToPCRel32GOTLoadRelaxable: 66 return "RequestGOTAndTransformToPCRel32GOTLoadRelaxable"; 67 case PCRel32TLVPLoadREXRelaxable: 68 return "PCRel32TLVPLoadREXRelaxable"; 69 case RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable: 70 return "RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable"; 71 default: 72 return getGenericEdgeKindName(static_cast<Edge::Kind>(K)); 73 } 74 } 75 76 const char NullPointerContent[PointerSize] = {0x00, 0x00, 0x00, 0x00, 77 0x00, 0x00, 0x00, 0x00}; 78 79 const char PointerJumpStubContent[6] = { 80 static_cast<char>(0xFFu), 0x25, 0x00, 0x00, 0x00, 0x00}; 81 82 Error optimizeGOTAndStubAccesses(LinkGraph &G) { 83 LLVM_DEBUG(dbgs() << "Optimizing GOT entries and stubs:\n"); 84 85 for (auto *B : G.blocks()) 86 for (auto &E : B->edges()) { 87 if (E.getKind() == x86_64::PCRel32GOTLoadRelaxable || 88 E.getKind() == x86_64::PCRel32GOTLoadREXRelaxable) { 89 #ifndef NDEBUG 90 bool REXPrefix = E.getKind() == x86_64::PCRel32GOTLoadREXRelaxable; 91 assert(E.getOffset() >= (REXPrefix ? 3u : 2u) && 92 "GOT edge occurs too early in block"); 93 #endif 94 auto *FixupData = reinterpret_cast<uint8_t *>( 95 const_cast<char *>(B->getContent().data())) + 96 E.getOffset(); 97 const uint8_t Op = FixupData[-2]; 98 const uint8_t ModRM = FixupData[-1]; 99 100 auto &GOTEntryBlock = E.getTarget().getBlock(); 101 assert(GOTEntryBlock.getSize() == G.getPointerSize() && 102 "GOT entry block should be pointer sized"); 103 assert(GOTEntryBlock.edges_size() == 1 && 104 "GOT entry should only have one outgoing edge"); 105 auto &GOTTarget = GOTEntryBlock.edges().begin()->getTarget(); 106 orc::ExecutorAddr TargetAddr = GOTTarget.getAddress(); 107 orc::ExecutorAddr EdgeAddr = B->getFixupAddress(E); 108 int64_t Displacement = TargetAddr - EdgeAddr + 4; 109 bool TargetInRangeForImmU32 = isUInt<32>(TargetAddr.getValue()); 110 bool DisplacementInRangeForImmS32 = isInt<32>(Displacement); 111 112 // If both of the Target and displacement is out of range, then 113 // there isn't optimization chance. 114 if (!(TargetInRangeForImmU32 || DisplacementInRangeForImmS32)) 115 continue; 116 117 // Transform "mov foo@GOTPCREL(%rip),%reg" to "lea foo(%rip),%reg". 118 if (Op == 0x8b && DisplacementInRangeForImmS32) { 119 FixupData[-2] = 0x8d; 120 E.setKind(x86_64::Delta32); 121 E.setTarget(GOTTarget); 122 E.setAddend(E.getAddend() - 4); 123 LLVM_DEBUG({ 124 dbgs() << " Replaced GOT load wih LEA:\n "; 125 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 126 dbgs() << "\n"; 127 }); 128 continue; 129 } 130 131 // Transform call/jmp instructions 132 if (Op == 0xff && TargetInRangeForImmU32) { 133 if (ModRM == 0x15) { 134 // ABI says we can convert "call *foo@GOTPCREL(%rip)" to "nop; call 135 // foo" But lld convert it to "addr32 call foo, because that makes 136 // result expression to be a single instruction. 137 FixupData[-2] = 0x67; 138 FixupData[-1] = 0xe8; 139 LLVM_DEBUG({ 140 dbgs() << " replaced call instruction's memory operand wih imm " 141 "operand:\n "; 142 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 143 dbgs() << "\n"; 144 }); 145 } else { 146 // Transform "jmp *foo@GOTPCREL(%rip)" to "jmp foo; nop" 147 assert(ModRM == 0x25 && "Invalid ModRm for call/jmp instructions"); 148 FixupData[-2] = 0xe9; 149 FixupData[3] = 0x90; 150 E.setOffset(E.getOffset() - 1); 151 LLVM_DEBUG({ 152 dbgs() << " replaced jmp instruction's memory operand wih imm " 153 "operand:\n "; 154 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 155 dbgs() << "\n"; 156 }); 157 } 158 E.setKind(x86_64::Pointer32); 159 E.setTarget(GOTTarget); 160 continue; 161 } 162 } else if (E.getKind() == x86_64::BranchPCRel32ToPtrJumpStubBypassable) { 163 auto &StubBlock = E.getTarget().getBlock(); 164 assert(StubBlock.getSize() == sizeof(PointerJumpStubContent) && 165 "Stub block should be stub sized"); 166 assert(StubBlock.edges_size() == 1 && 167 "Stub block should only have one outgoing edge"); 168 169 auto &GOTBlock = StubBlock.edges().begin()->getTarget().getBlock(); 170 assert(GOTBlock.getSize() == G.getPointerSize() && 171 "GOT block should be pointer sized"); 172 assert(GOTBlock.edges_size() == 1 && 173 "GOT block should only have one outgoing edge"); 174 175 auto &GOTTarget = GOTBlock.edges().begin()->getTarget(); 176 orc::ExecutorAddr EdgeAddr = B->getAddress() + E.getOffset(); 177 orc::ExecutorAddr TargetAddr = GOTTarget.getAddress(); 178 179 int64_t Displacement = TargetAddr - EdgeAddr + 4; 180 if (isInt<32>(Displacement)) { 181 E.setKind(x86_64::BranchPCRel32); 182 E.setTarget(GOTTarget); 183 LLVM_DEBUG({ 184 dbgs() << " Replaced stub branch with direct branch:\n "; 185 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 186 dbgs() << "\n"; 187 }); 188 } 189 } 190 } 191 192 return Error::success(); 193 } 194 195 } // end namespace x86_64 196 } // end namespace jitlink 197 } // end namespace llvm 198