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