1 //===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===// 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 // This file implements edits function bodies in place to support the 10 // "patchable-function" attribute. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/CodeGen/MachineFunction.h" 15 #include "llvm/CodeGen/MachineFunctionPass.h" 16 #include "llvm/CodeGen/MachineInstrBuilder.h" 17 #include "llvm/CodeGen/Passes.h" 18 #include "llvm/CodeGen/TargetFrameLowering.h" 19 #include "llvm/CodeGen/TargetInstrInfo.h" 20 #include "llvm/CodeGen/TargetSubtargetInfo.h" 21 22 using namespace llvm; 23 24 namespace { 25 struct PatchableFunction : public MachineFunctionPass { 26 static char ID; // Pass identification, replacement for typeid 27 PatchableFunction() : MachineFunctionPass(ID) { 28 initializePatchableFunctionPass(*PassRegistry::getPassRegistry()); 29 } 30 31 bool runOnMachineFunction(MachineFunction &F) override; 32 MachineFunctionProperties getRequiredProperties() const override { 33 return MachineFunctionProperties().set( 34 MachineFunctionProperties::Property::NoVRegs); 35 } 36 }; 37 } 38 39 /// Returns true if instruction \p MI will not result in actual machine code 40 /// instructions. 41 static bool doesNotGeneratecode(const MachineInstr &MI) { 42 // TODO: Introduce an MCInstrDesc flag for this 43 switch (MI.getOpcode()) { 44 default: return false; 45 case TargetOpcode::IMPLICIT_DEF: 46 case TargetOpcode::KILL: 47 case TargetOpcode::CFI_INSTRUCTION: 48 case TargetOpcode::EH_LABEL: 49 case TargetOpcode::GC_LABEL: 50 case TargetOpcode::DBG_VALUE: 51 case TargetOpcode::DBG_LABEL: 52 return true; 53 } 54 } 55 56 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) { 57 if (!MF.getFunction().hasFnAttribute("patchable-function")) 58 return false; 59 60 #ifndef NDEBUG 61 Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function"); 62 StringRef PatchType = PatchAttr.getValueAsString(); 63 assert(PatchType == "prologue-short-redirect" && "Only possibility today!"); 64 #endif 65 66 auto &FirstMBB = *MF.begin(); 67 MachineBasicBlock::iterator FirstActualI = FirstMBB.begin(); 68 for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI) 69 assert(FirstActualI != FirstMBB.end()); 70 71 auto *TII = MF.getSubtarget().getInstrInfo(); 72 auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(), 73 TII->get(TargetOpcode::PATCHABLE_OP)) 74 .addImm(2) 75 .addImm(FirstActualI->getOpcode()); 76 77 for (auto &MO : FirstActualI->operands()) 78 MIB.add(MO); 79 80 FirstActualI->eraseFromParent(); 81 MF.ensureAlignment(Align(16)); 82 return true; 83 } 84 85 char PatchableFunction::ID = 0; 86 char &llvm::PatchableFunctionID = PatchableFunction::ID; 87 INITIALIZE_PASS(PatchableFunction, "patchable-function", 88 "Implement the 'patchable-function' attribute", false, false) 89