1 //===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file implements edits function bodies in place to support the 11 // "patchable-function" attribute. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/CodeGen/Passes.h" 16 #include "llvm/CodeGen/MachineFunction.h" 17 #include "llvm/CodeGen/MachineFunctionPass.h" 18 #include "llvm/CodeGen/MachineInstrBuilder.h" 19 #include "llvm/Target/TargetFrameLowering.h" 20 #include "llvm/Target/TargetInstrInfo.h" 21 #include "llvm/Target/TargetSubtargetInfo.h" 22 23 using namespace llvm; 24 25 namespace { 26 struct PatchableFunction : public MachineFunctionPass { 27 static char ID; // Pass identification, replacement for typeid PatchableFunction__anonc402d89f0111::PatchableFunction28 PatchableFunction() : MachineFunctionPass(ID) { 29 initializePatchableFunctionPass(*PassRegistry::getPassRegistry()); 30 } 31 32 bool runOnMachineFunction(MachineFunction &F) override; getRequiredProperties__anonc402d89f0111::PatchableFunction33 MachineFunctionProperties getRequiredProperties() const override { 34 return MachineFunctionProperties().set( 35 MachineFunctionProperties::Property::AllVRegsAllocated); 36 } 37 }; 38 } 39 40 /// Returns true if instruction \p MI will not result in actual machine code 41 /// instructions. doesNotGeneratecode(const MachineInstr & MI)42static 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 return true; 53 } 54 } 55 runOnMachineFunction(MachineFunction & MF)56bool 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.addOperand(MO); 79 80 FirstActualI->eraseFromParent(); 81 MF.ensureAlignment(4); 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