| //===----- BPFMISimplifyPatchable.cpp - MI Simplify Patchable Insts -------===// |
| // |
| // 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 |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass targets a subset of instructions like below |
| // ld_imm64 r1, @global |
| // ldd r2, r1, 0 |
| // add r3, struct_base_reg, r2 |
| // |
| // Here @global should represent an AMA (abstruct member access). |
| // Such an access is subject to bpf load time patching. After this pass, the |
| // code becomes |
| // ld_imm64 r1, @global |
| // add r3, struct_base_reg, r1 |
| // |
| // Eventually, at BTF output stage, a relocation record will be generated |
| // for ld_imm64 which should be replaced later by bpf loader: |
| // r1 = <calculated field_info> |
| // add r3, struct_base_reg, r1 |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "BPF.h" |
| #include "BPFCORE.h" |
| #include "BPFInstrInfo.h" |
| #include "BPFTargetMachine.h" |
| #include "llvm/CodeGen/MachineInstrBuilder.h" |
| #include "llvm/CodeGen/MachineRegisterInfo.h" |
| |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "bpf-mi-simplify-patchable" |
| |
| namespace { |
| |
| struct BPFMISimplifyPatchable : public MachineFunctionPass { |
| |
| static char ID; |
| const BPFInstrInfo *TII; |
| MachineFunction *MF; |
| |
| BPFMISimplifyPatchable() : MachineFunctionPass(ID) { |
| initializeBPFMISimplifyPatchablePass(*PassRegistry::getPassRegistry()); |
| } |
| |
| private: |
| // Initialize class variables. |
| void initialize(MachineFunction &MFParm); |
| |
| bool removeLD(void); |
| |
| public: |
| // Main entry point for this pass. |
| bool runOnMachineFunction(MachineFunction &MF) override { |
| if (!skipFunction(MF.getFunction())) { |
| initialize(MF); |
| } |
| return removeLD(); |
| } |
| }; |
| |
| // Initialize class variables. |
| void BPFMISimplifyPatchable::initialize(MachineFunction &MFParm) { |
| MF = &MFParm; |
| TII = MF->getSubtarget<BPFSubtarget>().getInstrInfo(); |
| LLVM_DEBUG(dbgs() << "*** BPF simplify patchable insts pass ***\n\n"); |
| } |
| |
| /// Remove unneeded Load instructions. |
| bool BPFMISimplifyPatchable::removeLD() { |
| MachineRegisterInfo *MRI = &MF->getRegInfo(); |
| MachineInstr *ToErase = nullptr; |
| bool Changed = false; |
| |
| for (MachineBasicBlock &MBB : *MF) { |
| for (MachineInstr &MI : MBB) { |
| if (ToErase) { |
| ToErase->eraseFromParent(); |
| ToErase = nullptr; |
| } |
| |
| // Ensure the register format is LOAD <reg>, <reg>, 0 |
| if (MI.getOpcode() != BPF::LDD && MI.getOpcode() != BPF::LDW && |
| MI.getOpcode() != BPF::LDH && MI.getOpcode() != BPF::LDB && |
| MI.getOpcode() != BPF::LDW32 && MI.getOpcode() != BPF::LDH32 && |
| MI.getOpcode() != BPF::LDB32) |
| continue; |
| |
| if (!MI.getOperand(0).isReg() || !MI.getOperand(1).isReg()) |
| continue; |
| |
| if (!MI.getOperand(2).isImm() || MI.getOperand(2).getImm()) |
| continue; |
| |
| Register DstReg = MI.getOperand(0).getReg(); |
| Register SrcReg = MI.getOperand(1).getReg(); |
| |
| MachineInstr *DefInst = MRI->getUniqueVRegDef(SrcReg); |
| if (!DefInst) |
| continue; |
| |
| bool IsCandidate = false; |
| if (DefInst->getOpcode() == BPF::LD_imm64) { |
| const MachineOperand &MO = DefInst->getOperand(1); |
| if (MO.isGlobal()) { |
| const GlobalValue *GVal = MO.getGlobal(); |
| auto *GVar = dyn_cast<GlobalVariable>(GVal); |
| if (GVar) { |
| // Global variables representing structure offset or |
| // patchable extern globals. |
| if (GVar->hasAttribute(BPFCoreSharedInfo::AmaAttr)) { |
| assert(MI.getOperand(2).getImm() == 0); |
| IsCandidate = true; |
| } |
| } |
| } |
| } |
| |
| if (!IsCandidate) |
| continue; |
| |
| auto Begin = MRI->use_begin(DstReg), End = MRI->use_end(); |
| decltype(End) NextI; |
| for (auto I = Begin; I != End; I = NextI) { |
| NextI = std::next(I); |
| I->setReg(SrcReg); |
| } |
| |
| ToErase = &MI; |
| Changed = true; |
| } |
| } |
| |
| return Changed; |
| } |
| |
| } // namespace |
| |
| INITIALIZE_PASS(BPFMISimplifyPatchable, DEBUG_TYPE, |
| "BPF PreEmit SimplifyPatchable", false, false) |
| |
| char BPFMISimplifyPatchable::ID = 0; |
| FunctionPass *llvm::createBPFMISimplifyPatchablePass() { |
| return new BPFMISimplifyPatchable(); |
| } |