1 //===-- CodeGen/AsmPrinter/WinCFGuard.cpp - Control Flow Guard Impl ------===// 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 contains support for writing the metadata for Windows Control Flow 10 // Guard, including address-taken functions, and valid longjmp targets. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "WinCFGuard.h" 15 #include "llvm/CodeGen/AsmPrinter.h" 16 #include "llvm/CodeGen/MachineFunction.h" 17 #include "llvm/CodeGen/MachineModuleInfo.h" 18 #include "llvm/CodeGen/MachineOperand.h" 19 #include "llvm/IR/Constants.h" 20 #include "llvm/IR/Metadata.h" 21 #include "llvm/MC/MCAsmInfo.h" 22 #include "llvm/MC/MCObjectFileInfo.h" 23 #include "llvm/MC/MCStreamer.h" 24 25 #include <vector> 26 27 using namespace llvm; 28 29 WinCFGuard::WinCFGuard(AsmPrinter *A) : AsmPrinterHandler(), Asm(A) {} 30 31 WinCFGuard::~WinCFGuard() {} 32 33 void WinCFGuard::endFunction(const MachineFunction *MF) { 34 35 // Skip functions without any longjmp targets. 36 if (MF->getLongjmpTargets().empty()) 37 return; 38 39 // Copy the function's longjmp targets to a module-level list. 40 LongjmpTargets.insert(LongjmpTargets.end(), MF->getLongjmpTargets().begin(), 41 MF->getLongjmpTargets().end()); 42 } 43 44 void WinCFGuard::endModule() { 45 const Module *M = Asm->MMI->getModule(); 46 std::vector<const Function *> Functions; 47 for (const Function &F : *M) 48 if (F.hasAddressTaken()) 49 Functions.push_back(&F); 50 if (Functions.empty() && LongjmpTargets.empty()) 51 return; 52 auto &OS = *Asm->OutStreamer; 53 OS.SwitchSection(Asm->OutContext.getObjectFileInfo()->getGFIDsSection()); 54 for (const Function *F : Functions) 55 OS.EmitCOFFSymbolIndex(Asm->getSymbol(F)); 56 57 // Emit the symbol index of each longjmp target. 58 OS.SwitchSection(Asm->OutContext.getObjectFileInfo()->getGLJMPSection()); 59 for (const MCSymbol *S : LongjmpTargets) { 60 OS.EmitCOFFSymbolIndex(S); 61 } 62 } 63