LLVM  9.0.0svn
XRayInstrumentation.cpp
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1 //===- XRayInstrumentation.cpp - Adds XRay instrumentation to functions. --===//
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 a MachineFunctionPass that inserts the appropriate
10 // XRay instrumentation instructions. We look for XRay-specific attributes
11 // on the function to determine whether we should insert the replacement
12 // operations.
13 //
14 //===---------------------------------------------------------------------===//
15 
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/Triple.h"
27 #include "llvm/IR/Attributes.h"
28 #include "llvm/IR/Function.h"
29 #include "llvm/Pass.h"
31 
32 using namespace llvm;
33 
34 namespace {
35 
36 struct InstrumentationOptions {
37  // Whether to emit PATCHABLE_TAIL_CALL.
38  bool HandleTailcall;
39 
40  // Whether to emit PATCHABLE_RET/PATCHABLE_FUNCTION_EXIT for all forms of
41  // return, e.g. conditional return.
42  bool HandleAllReturns;
43 };
44 
45 struct XRayInstrumentation : public MachineFunctionPass {
46  static char ID;
47 
48  XRayInstrumentation() : MachineFunctionPass(ID) {
50  }
51 
52  void getAnalysisUsage(AnalysisUsage &AU) const override {
53  AU.setPreservesCFG();
57  }
58 
59  bool runOnMachineFunction(MachineFunction &MF) override;
60 
61 private:
62  // Replace the original RET instruction with the exit sled code ("patchable
63  // ret" pseudo-instruction), so that at runtime XRay can replace the sled
64  // with a code jumping to XRay trampoline, which calls the tracing handler
65  // and, in the end, issues the RET instruction.
66  // This is the approach to go on CPUs which have a single RET instruction,
67  // like x86/x86_64.
68  void replaceRetWithPatchableRet(MachineFunction &MF,
69  const TargetInstrInfo *TII,
70  InstrumentationOptions);
71 
72  // Prepend the original return instruction with the exit sled code ("patchable
73  // function exit" pseudo-instruction), preserving the original return
74  // instruction just after the exit sled code.
75  // This is the approach to go on CPUs which have multiple options for the
76  // return instruction, like ARM. For such CPUs we can't just jump into the
77  // XRay trampoline and issue a single return instruction there. We rather
78  // have to call the trampoline and return from it to the original return
79  // instruction of the function being instrumented.
80  void prependRetWithPatchableExit(MachineFunction &MF,
81  const TargetInstrInfo *TII,
82  InstrumentationOptions);
83 };
84 
85 } // end anonymous namespace
86 
87 void XRayInstrumentation::replaceRetWithPatchableRet(
89  InstrumentationOptions op) {
90  // We look for *all* terminators and returns, then replace those with
91  // PATCHABLE_RET instructions.
93  for (auto &MBB : MF) {
94  for (auto &T : MBB.terminators()) {
95  unsigned Opc = 0;
96  if (T.isReturn() &&
97  (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
98  // Replace return instructions with:
99  // PATCHABLE_RET <Opcode>, <Operand>...
100  Opc = TargetOpcode::PATCHABLE_RET;
101  }
102  if (TII->isTailCall(T) && op.HandleTailcall) {
103  // Treat the tail call as a return instruction, which has a
104  // different-looking sled than the normal return case.
105  Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
106  }
107  if (Opc != 0) {
108  auto MIB = BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc))
109  .addImm(T.getOpcode());
110  for (auto &MO : T.operands())
111  MIB.add(MO);
112  Terminators.push_back(&T);
113  }
114  }
115  }
116 
117  for (auto &I : Terminators)
118  I->eraseFromParent();
119 }
120 
121 void XRayInstrumentation::prependRetWithPatchableExit(
122  MachineFunction &MF, const TargetInstrInfo *TII,
123  InstrumentationOptions op) {
124  for (auto &MBB : MF)
125  for (auto &T : MBB.terminators()) {
126  unsigned Opc = 0;
127  if (T.isReturn() &&
128  (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
129  Opc = TargetOpcode::PATCHABLE_FUNCTION_EXIT;
130  }
131  if (TII->isTailCall(T) && op.HandleTailcall) {
132  Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
133  }
134  if (Opc != 0) {
135  // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT or
136  // PATCHABLE_TAIL_CALL .
137  BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc));
138  }
139  }
140 }
141 
142 bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
143  auto &F = MF.getFunction();
144  auto InstrAttr = F.getFnAttribute("function-instrument");
145  bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) &&
146  InstrAttr.isStringAttribute() &&
147  InstrAttr.getValueAsString() == "xray-always";
148  Attribute Attr = F.getFnAttribute("xray-instruction-threshold");
149  unsigned XRayThreshold = 0;
150  if (!AlwaysInstrument) {
151  if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute())
152  return false; // XRay threshold attribute not found.
153  if (Attr.getValueAsString().getAsInteger(10, XRayThreshold))
154  return false; // Invalid value for threshold.
155 
156  // Count the number of MachineInstr`s in MachineFunction
157  int64_t MICount = 0;
158  for (const auto &MBB : MF)
159  MICount += MBB.size();
160 
161  // Get MachineDominatorTree or compute it on the fly if it's unavailable
162  auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
163  MachineDominatorTree ComputedMDT;
164  if (!MDT) {
165  ComputedMDT.getBase().recalculate(MF);
166  MDT = &ComputedMDT;
167  }
168 
169  // Get MachineLoopInfo or compute it on the fly if it's unavailable
170  auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
171  MachineLoopInfo ComputedMLI;
172  if (!MLI) {
173  ComputedMLI.getBase().analyze(MDT->getBase());
174  MLI = &ComputedMLI;
175  }
176 
177  // Check if we have a loop.
178  // FIXME: Maybe make this smarter, and see whether the loops are dependent
179  // on inputs or side-effects?
180  if (MLI->empty() && MICount < XRayThreshold)
181  return false; // Function is too small and has no loops.
182  }
183 
184  // We look for the first non-empty MachineBasicBlock, so that we can insert
185  // the function instrumentation in the appropriate place.
186  auto MBI = llvm::find_if(
187  MF, [&](const MachineBasicBlock &MBB) { return !MBB.empty(); });
188  if (MBI == MF.end())
189  return false; // The function is empty.
190 
191  auto *TII = MF.getSubtarget().getInstrInfo();
192  auto &FirstMBB = *MBI;
193  auto &FirstMI = *FirstMBB.begin();
194 
195  if (!MF.getSubtarget().isXRaySupported()) {
196  FirstMI.emitError("An attempt to perform XRay instrumentation for an"
197  " unsupported target.");
198  return false;
199  }
200 
201  // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the
202  // MachineFunction.
203  BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
204  TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
205 
206  switch (MF.getTarget().getTargetTriple().getArch()) {
207  case Triple::ArchType::arm:
208  case Triple::ArchType::thumb:
209  case Triple::ArchType::aarch64:
210  case Triple::ArchType::mips:
211  case Triple::ArchType::mipsel:
212  case Triple::ArchType::mips64:
213  case Triple::ArchType::mips64el: {
214  // For the architectures which don't have a single return instruction
215  InstrumentationOptions op;
216  op.HandleTailcall = false;
217  op.HandleAllReturns = true;
218  prependRetWithPatchableExit(MF, TII, op);
219  break;
220  }
221  case Triple::ArchType::ppc64le: {
222  // PPC has conditional returns. Turn them into branch and plain returns.
223  InstrumentationOptions op;
224  op.HandleTailcall = false;
225  op.HandleAllReturns = true;
226  replaceRetWithPatchableRet(MF, TII, op);
227  break;
228  }
229  default: {
230  // For the architectures that have a single return instruction (such as
231  // RETQ on x86_64).
232  InstrumentationOptions op;
233  op.HandleTailcall = true;
234  op.HandleAllReturns = false;
235  replaceRetWithPatchableRet(MF, TII, op);
236  break;
237  }
238  }
239  return true;
240 }
241 
242 char XRayInstrumentation::ID = 0;
244 INITIALIZE_PASS_BEGIN(XRayInstrumentation, "xray-instrumentation",
245  "Insert XRay ops", false, false)
247 INITIALIZE_PASS_END(XRayInstrumentation, "xray-instrumentation",
248  "Insert XRay ops", false, false)
const MachineInstrBuilder & add(const MachineOperand &MO) const
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
This class represents lattice values for constants.
Definition: AllocatorList.h:23
void push_back(const T &Elt)
Definition: SmallVector.h:211
F(f)
#define op(i)
#define INITIALIZE_PASS_DEPENDENCY(depName)
Definition: PassSupport.h:50
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
bool isStringAttribute() const
Return true if the attribute is a string (target-dependent) attribute.
Definition: Attributes.cpp:169
const HexagonInstrInfo * TII
This file contains the simple types necessary to represent the attributes associated with functions a...
No attributes have been set.
Definition: Attributes.h:71
char & XRayInstrumentationID
This pass inserts the XRay instrumentation sleds if they are supported by the target platform...
TargetInstrInfo - Interface to description of machine instruction set.
void initializeXRayInstrumentationPass(PassRegistry &)
MachineInstrBuilder BuildMI(MachineFunction &MF, const DebugLoc &DL, const MCInstrDesc &MCID)
Builder interface. Specify how to create the initial instruction itself.
xray instrumentation
bool hasAttribute(AttrKind Val) const
Return true if the attribute is present.
Definition: Attributes.cpp:201
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
Represent the analysis usage information of a pass.
auto find_if(R &&Range, UnaryPredicate P) -> decltype(adl_begin(Range))
Provide wrappers to std::find_if which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:1213
INITIALIZE_PASS_END(RegBankSelect, DEBUG_TYPE, "Assign register bank of generic virtual registers", false, false) RegBankSelect
std::enable_if< std::numeric_limits< T >::is_signed, bool >::type getAsInteger(unsigned Radix, T &Result) const
Parse the current string as an integer of the specified radix.
Definition: StringRef.h:478
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:301
virtual bool isTailCall(const MachineInstr &Inst) const
Determines whether Inst is a tail call instruction.
const Function & getFunction() const
Return the LLVM function that this machine code represents.
unsigned getReturnOpcode() const
INITIALIZE_PASS_BEGIN(XRayInstrumentation, "xray-instrumentation", "Insert XRay ops", false, false) INITIALIZE_PASS_END(XRayInstrumentation
xray Insert XRay ops
StringRef getValueAsString() const
Return the attribute&#39;s value as a string.
Definition: Attributes.cpp:194
const MCInstrDesc & get(unsigned Opcode) const
Return the machine instruction descriptor that corresponds to the specified instruction opcode...
Definition: MCInstrInfo.h:44
#define I(x, y, z)
Definition: MD5.cpp:58
DomTreeBase< MachineBasicBlock > & getBase()
DominatorTree Class - Concrete subclass of DominatorTreeBase that is used to compute a normal dominat...
LoopInfoBase< MachineBasicBlock, MachineLoop > & getBase()