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 #include "llvm/InitializePasses.h" 22 23 using namespace llvm; 24 25 namespace { 26 struct PatchableFunction : public MachineFunctionPass { 27 static char ID; // Pass identification, replacement for typeid 28 PatchableFunction() : MachineFunctionPass(ID) { 29 initializePatchableFunctionPass(*PassRegistry::getPassRegistry()); 30 } 31 32 bool runOnMachineFunction(MachineFunction &F) override; 33 MachineFunctionProperties getRequiredProperties() const override { 34 return MachineFunctionProperties().set( 35 MachineFunctionProperties::Property::NoVRegs); 36 } 37 }; 38 } 39 40 /// Returns true if instruction \p MI will not result in actual machine code 41 /// instructions. 42 static bool doesNotGeneratecode(const MachineInstr &MI) { 43 // TODO: Introduce an MCInstrDesc flag for this 44 switch (MI.getOpcode()) { 45 default: return false; 46 case TargetOpcode::IMPLICIT_DEF: 47 case TargetOpcode::KILL: 48 case TargetOpcode::CFI_INSTRUCTION: 49 case TargetOpcode::EH_LABEL: 50 case TargetOpcode::GC_LABEL: 51 case TargetOpcode::DBG_VALUE: 52 case TargetOpcode::DBG_LABEL: 53 return true; 54 } 55 } 56 57 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) { 58 if (!MF.getFunction().hasFnAttribute("patchable-function")) 59 return false; 60 61 #ifndef NDEBUG 62 Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function"); 63 StringRef PatchType = PatchAttr.getValueAsString(); 64 assert(PatchType == "prologue-short-redirect" && "Only possibility today!"); 65 #endif 66 67 auto &FirstMBB = *MF.begin(); 68 MachineBasicBlock::iterator FirstActualI = FirstMBB.begin(); 69 for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI) 70 assert(FirstActualI != FirstMBB.end()); 71 72 auto *TII = MF.getSubtarget().getInstrInfo(); 73 auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(), 74 TII->get(TargetOpcode::PATCHABLE_OP)) 75 .addImm(2) 76 .addImm(FirstActualI->getOpcode()); 77 78 for (auto &MO : FirstActualI->operands()) 79 MIB.add(MO); 80 81 FirstActualI->eraseFromParent(); 82 MF.ensureAlignment(Align(16)); 83 return true; 84 } 85 86 char PatchableFunction::ID = 0; 87 char &llvm::PatchableFunctionID = PatchableFunction::ID; 88 INITIALIZE_PASS(PatchableFunction, "patchable-function", 89 "Implement the 'patchable-function' attribute", false, false) 90