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//===------ RISCVIndirectBranchTracking.cpp - Enables lpad mechanism ------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The pass adds LPAD (AUIPC with rs1 = X0) machine instructions at the
// beginning of each basic block or function that is referenced by an indirect
// jump/call instruction.
//
//===----------------------------------------------------------------------===//
#include "RISCV.h"
#include "RISCVInstrInfo.h"
#include "RISCVSubtarget.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#define DEBUG_TYPE "riscv-indrect-branch-tracking"
#define PASS_NAME "RISC-V Indirect Branch Tracking"
using namespace llvm;
cl::opt<uint32_t> PreferredLandingPadLabel(
"riscv-landing-pad-label", cl::ReallyHidden,
cl::desc("Use preferred fixed label for all labels"));
namespace {
class RISCVIndirectBranchTracking : public MachineFunctionPass {
public:
static char ID;
RISCVIndirectBranchTracking() : MachineFunctionPass(ID) {}
StringRef getPassName() const override { return PASS_NAME; }
bool runOnMachineFunction(MachineFunction &MF) override;
private:
const Align LpadAlign = Align(4);
};
} // end anonymous namespace
INITIALIZE_PASS(RISCVIndirectBranchTracking, DEBUG_TYPE, PASS_NAME, false,
false)
char RISCVIndirectBranchTracking::ID = 0;
FunctionPass *llvm::createRISCVIndirectBranchTrackingPass() {
return new RISCVIndirectBranchTracking();
}
static void emitLpad(MachineBasicBlock &MBB, const RISCVInstrInfo *TII,
uint32_t Label) {
auto I = MBB.begin();
BuildMI(MBB, I, MBB.findDebugLoc(I), TII->get(RISCV::AUIPC), RISCV::X0)
.addImm(Label);
}
bool RISCVIndirectBranchTracking::runOnMachineFunction(MachineFunction &MF) {
const auto &Subtarget = MF.getSubtarget<RISCVSubtarget>();
const RISCVInstrInfo *TII = Subtarget.getInstrInfo();
if (!Subtarget.hasStdExtZicfilp())
return false;
uint32_t FixedLabel = 0;
if (PreferredLandingPadLabel.getNumOccurrences() > 0) {
if (!isUInt<20>(PreferredLandingPadLabel))
report_fatal_error("riscv-landing-pad-label=<val>, <val> needs to fit in "
"unsigned 20-bits");
FixedLabel = PreferredLandingPadLabel;
}
bool Changed = false;
for (MachineBasicBlock &MBB : MF) {
if (&MBB == &MF.front()) {
Function &F = MF.getFunction();
// When trap is taken, landing pad is not needed.
if (F.hasFnAttribute("interrupt"))
continue;
if (F.hasAddressTaken() || !F.hasLocalLinkage()) {
emitLpad(MBB, TII, FixedLabel);
if (MF.getAlignment() < LpadAlign)
MF.setAlignment(LpadAlign);
Changed = true;
}
continue;
}
if (MBB.hasAddressTaken()) {
emitLpad(MBB, TII, FixedLabel);
if (MBB.getAlignment() < LpadAlign)
MBB.setAlignment(LpadAlign);
Changed = true;
}
}
return Changed;
}
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