llvm/lib/ExecutionEngine/JITLink/i386.cpp

   1 //===---- i386.cpp - Generic JITLink i386 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 i386 objects.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/ExecutionEngine/JITLink/i386.h"
  14
  15 #define DEBUG_TYPE "jitlink"
  16
  17 namespace llvm::jitlink::i386 {
  18
  19 const char *getEdgeKindName(Edge::Kind K) {
  20   switch (K) {
  21   case None:
  22     return "None";
  23   case Pointer32:
  24     return "Pointer32";
  25   case PCRel32:
  26     return "PCRel32";
  27   case Pointer16:
  28     return "Pointer16";
  29   case PCRel16:
  30     return "PCRel16";
  31   case Delta32:
  32     return "Delta32";
  33   case Delta32FromGOT:
  34     return "Delta32FromGOT";
  35   case RequestGOTAndTransformToDelta32FromGOT:
  36     return "RequestGOTAndTransformToDelta32FromGOT";
  37   case BranchPCRel32:
  38     return "BranchPCRel32";
  39   case BranchPCRel32ToPtrJumpStub:
  40     return "BranchPCRel32ToPtrJumpStub";
  41   case BranchPCRel32ToPtrJumpStubBypassable:
  42     return "BranchPCRel32ToPtrJumpStubBypassable";
  43   }
  44
  45   return getGenericEdgeKindName(K);
  46 }
  47
  48 const char NullPointerContent[PointerSize] = {0x00, 0x00, 0x00, 0x00};
  49
  50 const char PointerJumpStubContent[6] = {
  51     static_cast<char>(0xFFu), 0x25, 0x00, 0x00, 0x00, 0x00};
  52
  53 Error optimizeGOTAndStubAccesses(LinkGraph &G) {
  54   LLVM_DEBUG(dbgs() << "Optimizing GOT entries and stubs:\n");
  55
  56   for (auto *B : G.blocks())
  57     for (auto &E : B->edges()) {
  58       if (E.getKind() == i386::BranchPCRel32ToPtrJumpStubBypassable) {
  59         auto &StubBlock = E.getTarget().getBlock();
  60         assert(StubBlock.getSize() == sizeof(PointerJumpStubContent) &&
  61                "Stub block should be stub sized");
  62         assert(StubBlock.edges_size() == 1 &&
  63                "Stub block should only have one outgoing edge");
  64
  65         auto &GOTBlock = StubBlock.edges().begin()->getTarget().getBlock();
  66         assert(GOTBlock.getSize() == G.getPointerSize() &&
  67                "GOT block should be pointer sized");
  68         assert(GOTBlock.edges_size() == 1 &&
  69                "GOT block should only have one outgoing edge");
  70
  71         auto &GOTTarget = GOTBlock.edges().begin()->getTarget();
  72         orc::ExecutorAddr EdgeAddr = B->getAddress() + E.getOffset();
  73         orc::ExecutorAddr TargetAddr = GOTTarget.getAddress();
  74
  75         int64_t Displacement = TargetAddr - EdgeAddr + 4;
  76         if (isInt<32>(Displacement)) {
  77           E.setKind(i386::BranchPCRel32);
  78           E.setTarget(GOTTarget);
  79           LLVM_DEBUG({
  80             dbgs() << "  Replaced stub branch with direct branch:\n    ";
  81             printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind()));
  82             dbgs() << "\n";
  83           });
  84         }
  85       }
  86     }
  87
  88   return Error::success();
  89 }
  90
  91 } // namespace llvm::jitlink::i386