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 Delta64: 28 return "Delta64"; 29 case Delta32: 30 return "Delta32"; 31 case NegDelta64: 32 return "NegDelta64"; 33 case NegDelta32: 34 return "NegDelta32"; 35 case Delta64FromGOT: 36 return "Delta64FromGOT"; 37 case BranchPCRel32: 38 return "BranchPCRel32"; 39 case BranchPCRel32ToPtrJumpStub: 40 return "BranchPCRel32ToPtrJumpStub"; 41 case BranchPCRel32ToPtrJumpStubBypassable: 42 return "BranchPCRel32ToPtrJumpStubBypassable"; 43 case RequestGOTAndTransformToDelta32: 44 return "RequestGOTAndTransformToDelta32"; 45 case RequestGOTAndTransformToDelta64: 46 return "RequestGOTAndTransformToDelta64"; 47 case RequestGOTAndTransformToDelta64FromGOT: 48 return "RequestGOTAndTransformToDelta64FromGOT"; 49 case PCRel32GOTLoadREXRelaxable: 50 return "PCRel32GOTLoadREXRelaxable"; 51 case RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable: 52 return "RequestGOTAndTransformToPCRel32GOTLoadREXRelaxable"; 53 case PCRel32GOTLoadRelaxable: 54 return "PCRel32GOTLoadRelaxable"; 55 case RequestGOTAndTransformToPCRel32GOTLoadRelaxable: 56 return "RequestGOTAndTransformToPCRel32GOTLoadRelaxable"; 57 case PCRel32TLVPLoadREXRelaxable: 58 return "PCRel32TLVPLoadREXRelaxable"; 59 case RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable: 60 return "RequestTLVPAndTransformToPCRel32TLVPLoadREXRelaxable"; 61 default: 62 return getGenericEdgeKindName(static_cast<Edge::Kind>(K)); 63 } 64 } 65 66 const char NullPointerContent[PointerSize] = {0x00, 0x00, 0x00, 0x00, 67 0x00, 0x00, 0x00, 0x00}; 68 69 const char PointerJumpStubContent[6] = { 70 static_cast<char>(0xFFu), 0x25, 0x00, 0x00, 0x00, 0x00}; 71 72 Error optimize_x86_64_GOTAndStubs(LinkGraph &G) { 73 LLVM_DEBUG(dbgs() << "Optimizing GOT entries and stubs:\n"); 74 75 for (auto *B : G.blocks()) 76 for (auto &E : B->edges()) { 77 if (E.getKind() == x86_64::PCRel32GOTLoadRelaxable || 78 E.getKind() == x86_64::PCRel32GOTLoadREXRelaxable) { 79 bool REXPrefix = E.getKind() == x86_64::PCRel32GOTLoadREXRelaxable; 80 assert(E.getOffset() >= (REXPrefix ? 3 : 2) && 81 "GOT edge occurs too early in block"); 82 auto *FixupData = reinterpret_cast<uint8_t *>( 83 const_cast<char *>(B->getContent().data())) + 84 E.getOffset(); 85 const uint8_t Op = FixupData[-2]; 86 const uint8_t ModRM = FixupData[-1]; 87 88 auto &GOTEntryBlock = E.getTarget().getBlock(); 89 assert(GOTEntryBlock.getSize() == G.getPointerSize() && 90 "GOT entry block should be pointer sized"); 91 assert(GOTEntryBlock.edges_size() == 1 && 92 "GOT entry should only have one outgoing edge"); 93 auto &GOTTarget = GOTEntryBlock.edges().begin()->getTarget(); 94 JITTargetAddress TargetAddr = GOTTarget.getAddress(); 95 JITTargetAddress EdgeAddr = B->getFixupAddress(E); 96 int64_t Displacement = TargetAddr - EdgeAddr + 4; 97 bool TargetInRangeForImmU32 = isInRangeForImmU32(TargetAddr); 98 bool DisplacementInRangeForImmS32 = isInRangeForImmS32(Displacement); 99 100 // If both of the Target and displacement is out of range, then 101 // there isn't optimization chance. 102 if (!(TargetInRangeForImmU32 || DisplacementInRangeForImmS32)) 103 continue; 104 105 // Transform "mov foo@GOTPCREL(%rip),%reg" to "lea foo(%rip),%reg". 106 if (Op == 0x8b && DisplacementInRangeForImmS32) { 107 FixupData[-2] = 0x8d; 108 E.setKind(x86_64::Delta32); 109 E.setTarget(GOTTarget); 110 E.setAddend(E.getAddend() - 4); 111 LLVM_DEBUG({ 112 dbgs() << " Replaced GOT load wih LEA:\n "; 113 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 114 dbgs() << "\n"; 115 }); 116 continue; 117 } 118 119 // Transform call/jmp instructions 120 if (Op == 0xff && TargetInRangeForImmU32) { 121 if (ModRM == 0x15) { 122 // ABI says we can convert "call *foo@GOTPCREL(%rip)" to "nop; call 123 // foo" But lld convert it to "addr32 call foo, because that makes 124 // result expression to be a single instruction. 125 FixupData[-2] = 0x67; 126 FixupData[-1] = 0xe8; 127 LLVM_DEBUG({ 128 dbgs() << " replaced call instruction's memory operand wih imm " 129 "operand:\n "; 130 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 131 dbgs() << "\n"; 132 }); 133 } else { 134 // Transform "jmp *foo@GOTPCREL(%rip)" to "jmp foo; nop" 135 assert(ModRM == 0x25 && "Invalid ModRm for call/jmp instructions"); 136 FixupData[-2] = 0xe9; 137 FixupData[3] = 0x90; 138 E.setOffset(E.getOffset() - 1); 139 LLVM_DEBUG({ 140 dbgs() << " replaced jmp instruction's memory operand wih imm " 141 "operand:\n "; 142 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 143 dbgs() << "\n"; 144 }); 145 } 146 E.setKind(x86_64::Pointer32); 147 E.setTarget(GOTTarget); 148 continue; 149 } 150 } else if (E.getKind() == x86_64::BranchPCRel32ToPtrJumpStubBypassable) { 151 auto &StubBlock = E.getTarget().getBlock(); 152 assert(StubBlock.getSize() == sizeof(PointerJumpStubContent) && 153 "Stub block should be stub sized"); 154 assert(StubBlock.edges_size() == 1 && 155 "Stub block should only have one outgoing edge"); 156 157 auto &GOTBlock = StubBlock.edges().begin()->getTarget().getBlock(); 158 assert(GOTBlock.getSize() == G.getPointerSize() && 159 "GOT block should be pointer sized"); 160 assert(GOTBlock.edges_size() == 1 && 161 "GOT block should only have one outgoing edge"); 162 163 auto &GOTTarget = GOTBlock.edges().begin()->getTarget(); 164 JITTargetAddress EdgeAddr = B->getAddress() + E.getOffset(); 165 JITTargetAddress TargetAddr = GOTTarget.getAddress(); 166 167 int64_t Displacement = TargetAddr - EdgeAddr + 4; 168 if (isInRangeForImmS32(Displacement)) { 169 E.setKind(x86_64::BranchPCRel32); 170 E.setTarget(GOTTarget); 171 LLVM_DEBUG({ 172 dbgs() << " Replaced stub branch with direct branch:\n "; 173 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind())); 174 dbgs() << "\n"; 175 }); 176 } 177 } 178 } 179 180 return Error::success(); 181 } 182 183 } // end namespace x86_64 184 } // end namespace jitlink 185 } // end namespace llvm 186