1 //===-------- x86.cpp - Generic JITLink x86 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 objects.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "llvm/ExecutionEngine/JITLink/x86.h"
14
15 #define DEBUG_TYPE "jitlink"
16
17 namespace llvm::jitlink::x86 {
18
getEdgeKindName(Edge::Kind K)19 const char *getEdgeKindName(Edge::Kind K) {
20 switch (K) {
21 case Pointer32:
22 return "Pointer32";
23 case PCRel32:
24 return "PCRel32";
25 case Pointer16:
26 return "Pointer16";
27 case PCRel16:
28 return "PCRel16";
29 case Delta32:
30 return "Delta32";
31 case Delta32FromGOT:
32 return "Delta32FromGOT";
33 case RequestGOTAndTransformToDelta32FromGOT:
34 return "RequestGOTAndTransformToDelta32FromGOT";
35 case BranchPCRel32:
36 return "BranchPCRel32";
37 case BranchPCRel32ToPtrJumpStub:
38 return "BranchPCRel32ToPtrJumpStub";
39 case BranchPCRel32ToPtrJumpStubBypassable:
40 return "BranchPCRel32ToPtrJumpStubBypassable";
41 }
42
43 return getGenericEdgeKindName(K);
44 }
45
46 const char NullPointerContent[PointerSize] = {0x00, 0x00, 0x00, 0x00};
47
48 const char PointerJumpStubContent[6] = {
49 static_cast<char>(0xFFu), 0x25, 0x00, 0x00, 0x00, 0x00};
50
optimizeGOTAndStubAccesses(LinkGraph & G)51 Error optimizeGOTAndStubAccesses(LinkGraph &G) {
52 LLVM_DEBUG(dbgs() << "Optimizing GOT entries and stubs:\n");
53
54 for (auto *B : G.blocks())
55 for (auto &E : B->edges()) {
56 if (E.getKind() == BranchPCRel32ToPtrJumpStubBypassable) {
57 auto &StubBlock = E.getTarget().getBlock();
58 assert(StubBlock.getSize() == sizeof(PointerJumpStubContent) &&
59 "Stub block should be stub sized");
60 assert(StubBlock.edges_size() == 1 &&
61 "Stub block should only have one outgoing edge");
62
63 auto &GOTBlock = StubBlock.edges().begin()->getTarget().getBlock();
64 assert(GOTBlock.getSize() == G.getPointerSize() &&
65 "GOT block should be pointer sized");
66 assert(GOTBlock.edges_size() == 1 &&
67 "GOT block should only have one outgoing edge");
68
69 auto &GOTTarget = GOTBlock.edges().begin()->getTarget();
70 orc::ExecutorAddr EdgeAddr = B->getAddress() + E.getOffset();
71 orc::ExecutorAddr TargetAddr = GOTTarget.getAddress();
72
73 int64_t Displacement = TargetAddr - EdgeAddr + 4;
74 if (isInt<32>(Displacement)) {
75 E.setKind(BranchPCRel32);
76 E.setTarget(GOTTarget);
77 LLVM_DEBUG({
78 dbgs() << " Replaced stub branch with direct branch:\n ";
79 printEdge(dbgs(), *B, E, getEdgeKindName(E.getKind()));
80 dbgs() << "\n";
81 });
82 }
83 }
84 }
85
86 return Error::success();
87 }
88
89 } // namespace llvm::jitlink::x86
90