llvm/lib/ExecutionEngine/JITLink/x86_64.cpp

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