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
17namespace llvm::jitlink::i386 {
18
19const 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
48const char NullPointerContent[PointerSize] = {0x00, 0x00, 0x00, 0x00};
49
50const char PointerJumpStubContent[6] = {
51 static_cast<char>(0xFFu), 0x25, 0x00, 0x00, 0x00, 0x00};
52
53Error 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>(x: 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
92