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
92