1 //===------ RISCVIndirectBranchTracking.cpp - Enables lpad mechanism ------===//
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 // The pass adds LPAD (AUIPC with rs1 = X0) machine instructions at the
10 // beginning of each basic block or function that is referenced by an indirect
11 // jump/call instruction.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "RISCV.h"
16 #include "RISCVInstrInfo.h"
17 #include "RISCVSubtarget.h"
18 #include "llvm/ADT/Statistic.h"
19 #include "llvm/CodeGen/MachineFunctionPass.h"
20 #include "llvm/CodeGen/MachineInstrBuilder.h"
21 #include "llvm/CodeGen/MachineModuleInfo.h"
22
23 #define DEBUG_TYPE "riscv-indrect-branch-tracking"
24 #define PASS_NAME "RISC-V Indirect Branch Tracking"
25
26 using namespace llvm;
27
28 cl::opt<uint32_t> PreferredLandingPadLabel(
29 "riscv-landing-pad-label", cl::ReallyHidden,
30 cl::desc("Use preferred fixed label for all labels"));
31
32 namespace {
33 class RISCVIndirectBranchTracking : public MachineFunctionPass {
34 public:
35 static char ID;
RISCVIndirectBranchTracking()36 RISCVIndirectBranchTracking() : MachineFunctionPass(ID) {}
37
getPassName() const38 StringRef getPassName() const override { return PASS_NAME; }
39
40 bool runOnMachineFunction(MachineFunction &MF) override;
41
42 private:
43 const Align LpadAlign = Align(4);
44 };
45
46 } // end anonymous namespace
47
48 INITIALIZE_PASS(RISCVIndirectBranchTracking, DEBUG_TYPE, PASS_NAME, false,
49 false)
50
51 char RISCVIndirectBranchTracking::ID = 0;
52
createRISCVIndirectBranchTrackingPass()53 FunctionPass *llvm::createRISCVIndirectBranchTrackingPass() {
54 return new RISCVIndirectBranchTracking();
55 }
56
emitLpad(MachineBasicBlock & MBB,const RISCVInstrInfo * TII,uint32_t Label)57 static void emitLpad(MachineBasicBlock &MBB, const RISCVInstrInfo *TII,
58 uint32_t Label) {
59 auto I = MBB.begin();
60 BuildMI(MBB, I, MBB.findDebugLoc(I), TII->get(RISCV::AUIPC), RISCV::X0)
61 .addImm(Label);
62 }
63
runOnMachineFunction(MachineFunction & MF)64 bool RISCVIndirectBranchTracking::runOnMachineFunction(MachineFunction &MF) {
65 const auto &Subtarget = MF.getSubtarget<RISCVSubtarget>();
66 const RISCVInstrInfo *TII = Subtarget.getInstrInfo();
67 if (!Subtarget.hasStdExtZicfilp())
68 return false;
69
70 uint32_t FixedLabel = 0;
71 if (PreferredLandingPadLabel.getNumOccurrences() > 0) {
72 if (!isUInt<20>(PreferredLandingPadLabel))
73 report_fatal_error("riscv-landing-pad-label=<val>, <val> needs to fit in "
74 "unsigned 20-bits");
75 FixedLabel = PreferredLandingPadLabel;
76 }
77
78 bool Changed = false;
79 for (MachineBasicBlock &MBB : MF) {
80 if (&MBB == &MF.front()) {
81 Function &F = MF.getFunction();
82 // When trap is taken, landing pad is not needed.
83 if (F.hasFnAttribute("interrupt"))
84 continue;
85
86 if (F.hasAddressTaken() || !F.hasLocalLinkage()) {
87 emitLpad(MBB, TII, FixedLabel);
88 if (MF.getAlignment() < LpadAlign)
89 MF.setAlignment(LpadAlign);
90 Changed = true;
91 }
92 continue;
93 }
94
95 if (MBB.hasAddressTaken()) {
96 emitLpad(MBB, TII, FixedLabel);
97 if (MBB.getAlignment() < LpadAlign)
98 MBB.setAlignment(LpadAlign);
99 Changed = true;
100 }
101 }
102
103 return Changed;
104 }
105