1 //===-- XRayInstrumentation.cpp - Adds XRay instrumentation to functions. -===// 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 a MachineFunctionPass that inserts the appropriate 11 // XRay instrumentation instructions. We look for XRay-specific attributes 12 // on the function to determine whether we should insert the replacement 13 // operations. 14 // 15 //===---------------------------------------------------------------------===// 16 17 #include "llvm/CodeGen/Analysis.h" 18 #include "llvm/CodeGen/MachineFunction.h" 19 #include "llvm/CodeGen/MachineFunctionPass.h" 20 #include "llvm/CodeGen/MachineInstrBuilder.h" 21 #include "llvm/CodeGen/Passes.h" 22 #include "llvm/Support/TargetRegistry.h" 23 #include "llvm/Target/TargetInstrInfo.h" 24 #include "llvm/Target/TargetSubtargetInfo.h" 25 26 using namespace llvm; 27 28 namespace { 29 struct XRayInstrumentation : public MachineFunctionPass { 30 static char ID; 31 32 XRayInstrumentation() : MachineFunctionPass(ID) { 33 initializeXRayInstrumentationPass(*PassRegistry::getPassRegistry()); 34 } 35 36 bool runOnMachineFunction(MachineFunction &MF) override; 37 }; 38 } 39 40 bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) { 41 auto &F = *MF.getFunction(); 42 auto InstrAttr = F.getFnAttribute("function-instrument"); 43 bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) && 44 InstrAttr.isStringAttribute() && 45 InstrAttr.getValueAsString() == "xray-always"; 46 Attribute Attr = F.getFnAttribute("xray-instruction-threshold"); 47 unsigned XRayThreshold = 0; 48 if (!AlwaysInstrument) { 49 if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute()) 50 return false; // XRay threshold attribute not found. 51 if (Attr.getValueAsString().getAsInteger(10, XRayThreshold)) 52 return false; // Invalid value for threshold. 53 if (F.size() < XRayThreshold) 54 return false; // Function is too small. 55 } 56 57 // FIXME: Do the loop triviality analysis here or in an earlier pass. 58 59 // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the 60 // MachineFunction. 61 auto &FirstMBB = *MF.begin(); 62 auto &FirstMI = *FirstMBB.begin(); 63 auto *TII = MF.getSubtarget().getInstrInfo(); 64 BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(), 65 TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER)); 66 67 // Then we look for *all* terminators and returns, then replace those with 68 // PATCHABLE_RET instructions. 69 SmallVector<MachineInstr *, 4> Terminators; 70 for (auto &MBB : MF) { 71 for (auto &T : MBB.terminators()) { 72 // FIXME: Handle tail calls here too? 73 if (T.isReturn() && T.getOpcode() == TII->getReturnOpcode()) { 74 // Replace return instructions with: 75 // PATCHABLE_RET <Opcode>, <Operand>... 76 auto MIB = BuildMI(MBB, T, T.getDebugLoc(), 77 TII->get(TargetOpcode::PATCHABLE_RET)) 78 .addImm(T.getOpcode()); 79 for (auto &MO : T.operands()) 80 MIB.addOperand(MO); 81 Terminators.push_back(&T); 82 break; 83 } 84 } 85 } 86 87 for (auto &I : Terminators) 88 I->eraseFromParent(); 89 90 return true; 91 } 92 93 char XRayInstrumentation::ID = 0; 94 char &llvm::XRayInstrumentationID = XRayInstrumentation::ID; 95 INITIALIZE_PASS(XRayInstrumentation, "xray-instrumentation", "Insert XRay ops", 96 false, false) 97
