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 Delta64: 32 return "Delta64"; 33 case Delta32: 34 return "Delta32"; 35 case NegDelta64: 36 return "NegDelta64"; 37 case NegDelta32: 38 return "NegDelta32"; 39 case Delta64FromGOT: 40 return "Delta64FromGOT"; 41 case PCRel32: 42 return "PCRel32"; 43 case BranchPCRel32: 44 return "BranchPCRel32"; 45 case BranchPCRel32ToPtrJumpStub: 46 return "BranchPCRel32ToPtrJumpStub"; 47 case BranchPCRel32ToPtrJumpStubBypassable: 48 return "BranchPCRel32ToPtrJumpStubBypassable"; 49 case RequestGOTAndTransformToDelta32: 50 return "RequestGOTAndTransformToDelta32"; 51 case RequestGOTAndTransformToDelta64: 52 return "RequestGOTAndTransformToDelta64"; 53 case RequestGOTAndTransformToDelta64FromGOT: 54 return "RequestGOTAndTransformToDelta64FromGOT"; 55 case PCRel32GOTLoadREXRelaxable: 56 return "PCRel32GOTLoadREXRelaxable"; 57 case RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable: 58 return "RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable"; 59 case PCRel32GOTLoadRelaxable: 60 return "PCRel32GOTLoadRelaxable"; 61 case RequestGOTAndTransformToPCRel32GOTLoadRelaxable: 62 return "RequestGOTAndTransformToPCRel32GOTLoadRelaxable"; 63 case PCRel32TLVPLoadREXRelaxable: 64 return "PCRel32TLVPLoadREXRelaxable"; 65 case RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable: 66 return "RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable"; 67 default: 68 return getGenericEdgeKindName(static_cast<Edge::Kind>(K)); 69 } 70 } 71 72 const char NullPointerContent[PointerSize] = {0x00, 0x00, 0x00, 0x00, 73 0x00, 0x00, 0x00, 0x00}; 74 75 const char PointerJumpStubContent[6] = { 76 static_cast<char>(0xFFu), 0x25, 0x00, 0x00, 0x00, 0x00}; 77 78 Error optimizeGOTAndStubAccesses(LinkGraph &G) { 79 LLVM_DEBUG(dbgs() << "Optimizing GOT entries and stubs:\n"); 80 81 for (auto *B : G.blocks()) 82 for (auto &E : B->edges()) { 83 if (E.getKind() == x86_64::PCRel32GOTLoadRelaxable || 84 E.getKind() == x86_64::PCRel32GOTLoadREXRelaxable) { 85 #ifndef NDEBUG 86 bool REXPrefix = E.getKind() == x86_64::PCRel32GOTLoadREXRelaxable; 87 assert(E.getOffset() >= (REXPrefix ? 3u : 2u) && 88 "GOT edge occurs too early in block"); 89 #endif 90 auto *FixupData = reinterpret_cast<uint8_t *>( 91 const_cast<char *>(B->getContent().data())) + 92 E.getOffset(); 93 const uint8_t Op = FixupData[-2]; 94 const uint8_t ModRM = FixupData[-1]; 95 96 auto &GOTEntryBlock = E.getTarget().getBlock(); 97 assert(GOTEntryBlock.getSize() == G.getPointerSize() && 98 "GOT entry block should be pointer sized"); 99 assert(GOTEntryBlock.edges_size() == 1 && 100 "GOT entry should only have one outgoing edge"); 101 auto &GOTTarget = GOTEntryBlock.edges().begin()->getTarget(); 102 orc::ExecutorAddr TargetAddr = GOTTarget.getAddress(); 103 orc::ExecutorAddr EdgeAddr = B->getFixupAddress(E); 104 int64_t Displacement = TargetAddr - EdgeAddr + 4; 105 bool TargetInRangeForImmU32 = isInRangeForImmU32(TargetAddr.getValue()); 106 bool DisplacementInRangeForImmS32 = isInRangeForImmS32(Displacement); 107 108 // If both of the Target and displacement is out of range, then 109 // there isn't optimization chance. 110 if (!(TargetInRangeForImmU32 || DisplacementInRangeForImmS32)) 111 continue; 112 113 // Transform "mov foo@GOTPCREL(%rip),%reg" to "lea foo(%rip),%reg". 114 if (Op == 0x8b && DisplacementInRangeForImmS32) { 115 FixupData[-2] = 0x8d; 116 E.setKind(x86_64::Delta32); 117 E.setTarget(GOTTarget); 118 E.setAddend(E.getAddend() - 4); 119 LLVM_DEBUG({ 120 dbgs() << " Replaced GOT load wih LEA:\n "; 121 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 122 dbgs() << "\n"; 123 }); 124 continue; 125 } 126 127 // Transform call/jmp instructions 128 if (Op == 0xff && TargetInRangeForImmU32) { 129 if (ModRM == 0x15) { 130 // ABI says we can convert "call *foo@GOTPCREL(%rip)" to "nop; call 131 // foo" But lld convert it to "addr32 call foo, because that makes 132 // result expression to be a single instruction. 133 FixupData[-2] = 0x67; 134 FixupData[-1] = 0xe8; 135 LLVM_DEBUG({ 136 dbgs() << " replaced call instruction's memory operand wih imm " 137 "operand:\n "; 138 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 139 dbgs() << "\n"; 140 }); 141 } else { 142 // Transform "jmp *foo@GOTPCREL(%rip)" to "jmp foo; nop" 143 assert(ModRM == 0x25 && "Invalid ModRm for call/jmp instructions"); 144 FixupData[-2] = 0xe9; 145 FixupData[3] = 0x90; 146 E.setOffset(E.getOffset() - 1); 147 LLVM_DEBUG({ 148 dbgs() << " replaced jmp instruction's memory operand wih imm " 149 "operand:\n "; 150 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 151 dbgs() << "\n"; 152 }); 153 } 154 E.setKind(x86_64::Pointer32); 155 E.setTarget(GOTTarget); 156 continue; 157 } 158 } else if (E.getKind() == x86_64::BranchPCRel32ToPtrJumpStubBypassable) { 159 auto &StubBlock = E.getTarget().getBlock(); 160 assert(StubBlock.getSize() == sizeof(PointerJumpStubContent) && 161 "Stub block should be stub sized"); 162 assert(StubBlock.edges_size() == 1 && 163 "Stub block should only have one outgoing edge"); 164 165 auto &GOTBlock = StubBlock.edges().begin()->getTarget().getBlock(); 166 assert(GOTBlock.getSize() == G.getPointerSize() && 167 "GOT block should be pointer sized"); 168 assert(GOTBlock.edges_size() == 1 && 169 "GOT block should only have one outgoing edge"); 170 171 auto &GOTTarget = GOTBlock.edges().begin()->getTarget(); 172 orc::ExecutorAddr EdgeAddr = B->getAddress() + E.getOffset(); 173 orc::ExecutorAddr TargetAddr = GOTTarget.getAddress(); 174 175 int64_t Displacement = TargetAddr - EdgeAddr + 4; 176 if (isInRangeForImmS32(Displacement)) { 177 E.setKind(x86_64::BranchPCRel32); 178 E.setTarget(GOTTarget); 179 LLVM_DEBUG({ 180 dbgs() << " Replaced stub branch with direct branch:\n "; 181 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 182 dbgs() << "\n"; 183 }); 184 } 185 } 186 } 187 188 return Error::success(); 189 } 190 191 } // end namespace x86_64 192 } // end namespace jitlink 193 } // end namespace llvm 194