LCOV - code coverage report
Current view: top level - lib/CodeGen - XRayInstrumentation.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 74 76 97.4 %
Date: 2018-06-17 00:07:59 Functions: 8 9 88.9 %
Legend: Lines: hit not hit

          Line data    Source code
       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/ADT/STLExtras.h"
      18             : #include "llvm/ADT/SmallVector.h"
      19             : #include "llvm/ADT/Triple.h"
      20             : #include "llvm/CodeGen/MachineBasicBlock.h"
      21             : #include "llvm/CodeGen/MachineDominators.h"
      22             : #include "llvm/CodeGen/MachineFunction.h"
      23             : #include "llvm/CodeGen/MachineFunctionPass.h"
      24             : #include "llvm/CodeGen/MachineInstrBuilder.h"
      25             : #include "llvm/CodeGen/MachineLoopInfo.h"
      26             : #include "llvm/CodeGen/TargetInstrInfo.h"
      27             : #include "llvm/CodeGen/TargetSubtargetInfo.h"
      28             : #include "llvm/IR/Attributes.h"
      29             : #include "llvm/IR/Function.h"
      30             : #include "llvm/Pass.h"
      31             : #include "llvm/Target/TargetMachine.h"
      32             : 
      33             : using namespace llvm;
      34             : 
      35             : namespace {
      36             : 
      37             : struct InstrumentationOptions {
      38             :   // Whether to emit PATCHABLE_TAIL_CALL.
      39             :   bool HandleTailcall;
      40             : 
      41             :   // Whether to emit PATCHABLE_RET/PATCHABLE_FUNCTION_EXIT for all forms of
      42             :   // return, e.g. conditional return.
      43             :   bool HandleAllReturns;
      44             : };
      45             : 
      46       22686 : struct XRayInstrumentation : public MachineFunctionPass {
      47             :   static char ID;
      48             : 
      49       22794 :   XRayInstrumentation() : MachineFunctionPass(ID) {
      50       22794 :     initializeXRayInstrumentationPass(*PassRegistry::getPassRegistry());
      51       22794 :   }
      52             : 
      53       22627 :   void getAnalysisUsage(AnalysisUsage &AU) const override {
      54       22627 :     AU.setPreservesCFG();
      55             :     AU.addPreserved<MachineLoopInfo>();
      56             :     AU.addPreserved<MachineDominatorTree>();
      57       22627 :     MachineFunctionPass::getAnalysisUsage(AU);
      58       22627 :   }
      59             : 
      60             :   bool runOnMachineFunction(MachineFunction &MF) override;
      61             : 
      62             : private:
      63             :   // Replace the original RET instruction with the exit sled code ("patchable
      64             :   //   ret" pseudo-instruction), so that at runtime XRay can replace the sled
      65             :   //   with a code jumping to XRay trampoline, which calls the tracing handler
      66             :   //   and, in the end, issues the RET instruction.
      67             :   // This is the approach to go on CPUs which have a single RET instruction,
      68             :   //   like x86/x86_64.
      69             :   void replaceRetWithPatchableRet(MachineFunction &MF,
      70             :                                   const TargetInstrInfo *TII,
      71             :                                   InstrumentationOptions);
      72             : 
      73             :   // Prepend the original return instruction with the exit sled code ("patchable
      74             :   //   function exit" pseudo-instruction), preserving the original return
      75             :   //   instruction just after the exit sled code.
      76             :   // This is the approach to go on CPUs which have multiple options for the
      77             :   //   return instruction, like ARM. For such CPUs we can't just jump into the
      78             :   //   XRay trampoline and issue a single return instruction there. We rather
      79             :   //   have to call the trampoline and return from it to the original return
      80             :   //   instruction of the function being instrumented.
      81             :   void prependRetWithPatchableExit(MachineFunction &MF,
      82             :                                    const TargetInstrInfo *TII,
      83             :                                    InstrumentationOptions);
      84             : };
      85             : 
      86             : } // end anonymous namespace
      87             : 
      88          36 : void XRayInstrumentation::replaceRetWithPatchableRet(
      89             :     MachineFunction &MF, const TargetInstrInfo *TII,
      90             :     InstrumentationOptions op) {
      91             :   // We look for *all* terminators and returns, then replace those with
      92             :   // PATCHABLE_RET instructions.
      93             :   SmallVector<MachineInstr *, 4> Terminators;
      94          91 :   for (auto &MBB : MF) {
      95         165 :     for (auto &T : MBB.terminators()) {
      96             :       unsigned Opc = 0;
      97          99 :       if (T.isReturn() &&
      98         104 :           (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
      99             :         // Replace return instructions with:
     100             :         //   PATCHABLE_RET <Opcode>, <Operand>...
     101             :         Opc = TargetOpcode::PATCHABLE_RET;
     102             :       }
     103          55 :       if (TII->isTailCall(T) && op.HandleTailcall) {
     104             :         // Treat the tail call as a return instruction, which has a
     105             :         // different-looking sled than the normal return case.
     106             :         Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
     107             :       }
     108          51 :       if (Opc != 0) {
     109          88 :         auto MIB = BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc))
     110          88 :                        .addImm(T.getOpcode());
     111         230 :         for (auto &MO : T.operands())
     112             :           MIB.add(MO);
     113          44 :         Terminators.push_back(&T);
     114             :       }
     115             :     }
     116             :   }
     117             : 
     118         124 :   for (auto &I : Terminators)
     119          44 :     I->eraseFromParent();
     120          36 : }
     121             : 
     122          35 : void XRayInstrumentation::prependRetWithPatchableExit(
     123             :     MachineFunction &MF, const TargetInstrInfo *TII,
     124             :     InstrumentationOptions op) {
     125          78 :   for (auto &MBB : MF)
     126         129 :     for (auto &T : MBB.terminators()) {
     127             :       unsigned Opc = 0;
     128          82 :       if (T.isReturn() &&
     129          39 :           (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
     130             :         Opc = TargetOpcode::PATCHABLE_FUNCTION_EXIT;
     131             :       }
     132          43 :       if (TII->isTailCall(T) && op.HandleTailcall) {
     133             :         Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
     134             :       }
     135          43 :       if (Opc != 0) {
     136             :         // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT or
     137             :         //   PATCHABLE_TAIL_CALL .
     138          78 :         BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc));
     139             :       }
     140             :     }
     141          35 : }
     142             : 
     143      227101 : bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
     144      227101 :   auto &F = MF.getFunction();
     145      227101 :   auto InstrAttr = F.getFnAttribute("function-instrument");
     146      227167 :   bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) &&
     147      227101 :                           InstrAttr.isStringAttribute() &&
     148          66 :                           InstrAttr.getValueAsString() == "xray-always";
     149      227101 :   Attribute Attr = F.getFnAttribute("xray-instruction-threshold");
     150             :   unsigned XRayThreshold = 0;
     151      227101 :   if (!AlwaysInstrument) {
     152      227035 :     if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute())
     153      227030 :       return false; // XRay threshold attribute not found.
     154          14 :     if (Attr.getValueAsString().getAsInteger(10, XRayThreshold))
     155             :       return false; // Invalid value for threshold.
     156             : 
     157             :     // Count the number of MachineInstr`s in MachineFunction
     158             :     int64_t MICount = 0;
     159          20 :     for (const auto &MBB : MF)
     160          13 :       MICount += MBB.size();
     161             : 
     162             :     // Get MachineDominatorTree or compute it on the fly if it's unavailable
     163           7 :     auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
     164          12 :     MachineDominatorTree ComputedMDT;
     165           7 :     if (!MDT) {
     166           7 :       ComputedMDT.getBase().recalculate(MF);
     167             :       MDT = &ComputedMDT;
     168             :     }
     169             : 
     170             :     // Get MachineLoopInfo or compute it on the fly if it's unavailable
     171           7 :     auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
     172           7 :     MachineLoopInfo ComputedMLI;
     173           7 :     if (!MLI) {
     174           7 :       ComputedMLI.getBase().analyze(MDT->getBase());
     175             :       MLI = &ComputedMLI;
     176             :     }
     177             : 
     178             :     // Check if we have a loop.
     179             :     // FIXME: Maybe make this smarter, and see whether the loops are dependent
     180             :     // on inputs or side-effects?
     181           7 :     if (MLI->empty() && MICount < XRayThreshold)
     182             :       return false; // Function is too small and has no loops.
     183             :   }
     184             : 
     185             :   // We look for the first non-empty MachineBasicBlock, so that we can insert
     186             :   // the function instrumentation in the appropriate place.
     187             :   auto MBI = llvm::find_if(
     188             :       MF, [&](const MachineBasicBlock &MBB) { return !MBB.empty(); });
     189          71 :   if (MBI == MF.end())
     190             :     return false; // The function is empty.
     191             : 
     192          71 :   auto *TII = MF.getSubtarget().getInstrInfo();
     193             :   auto &FirstMBB = *MBI;
     194             :   auto &FirstMI = *FirstMBB.begin();
     195             : 
     196          71 :   if (!MF.getSubtarget().isXRaySupported()) {
     197           0 :     FirstMI.emitError("An attempt to perform XRay instrumentation for an"
     198             :                       " unsupported target.");
     199           0 :     return false;
     200             :   }
     201             : 
     202             :   // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the
     203             :   // MachineFunction.
     204          71 :   BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
     205          71 :           TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
     206             : 
     207          71 :   switch (MF.getTarget().getTargetTriple().getArch()) {
     208          35 :   case Triple::ArchType::arm:
     209             :   case Triple::ArchType::thumb:
     210             :   case Triple::ArchType::aarch64:
     211             :   case Triple::ArchType::mips:
     212             :   case Triple::ArchType::mipsel:
     213             :   case Triple::ArchType::mips64:
     214             :   case Triple::ArchType::mips64el: {
     215             :     // For the architectures which don't have a single return instruction
     216             :     InstrumentationOptions op;
     217          35 :     op.HandleTailcall = false;
     218          35 :     op.HandleAllReturns = true;
     219          35 :     prependRetWithPatchableExit(MF, TII, op);
     220             :     break;
     221             :   }
     222           8 :   case Triple::ArchType::ppc64le: {
     223             :     // PPC has conditional returns. Turn them into branch and plain returns.
     224             :     InstrumentationOptions op;
     225           8 :     op.HandleTailcall = false;
     226           8 :     op.HandleAllReturns = true;
     227           8 :     replaceRetWithPatchableRet(MF, TII, op);
     228             :     break;
     229             :   }
     230          28 :   default: {
     231             :     // For the architectures that have a single return instruction (such as
     232             :     //   RETQ on x86_64).
     233             :     InstrumentationOptions op;
     234          28 :     op.HandleTailcall = true;
     235          28 :     op.HandleAllReturns = false;
     236          28 :     replaceRetWithPatchableRet(MF, TII, op);
     237             :     break;
     238             :   }
     239             :   }
     240             :   return true;
     241             : }
     242             : 
     243             : char XRayInstrumentation::ID = 0;
     244             : char &llvm::XRayInstrumentationID = XRayInstrumentation::ID;
     245       26770 : INITIALIZE_PASS_BEGIN(XRayInstrumentation, "xray-instrumentation",
     246             :                       "Insert XRay ops", false, false)
     247       26770 : INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
     248      193700 : INITIALIZE_PASS_END(XRayInstrumentation, "xray-instrumentation",
     249             :                     "Insert XRay ops", false, false)

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