LLVM  16.0.0git
X86AvoidTrailingCall.cpp
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1 //===----- X86AvoidTrailingCall.cpp - Insert int3 after trailing calls ----===//
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 // The Windows x64 unwinder decodes the instruction stream during unwinding.
10 // The unwinder decodes forward from the current PC to detect epilogue code
11 // patterns.
12 //
13 // First, this means that there must be an instruction after every
14 // call instruction for the unwinder to decode. LLVM must maintain the invariant
15 // that the last instruction of a function or funclet is not a call, or the
16 // unwinder may decode into the next function. Similarly, a call may not
17 // immediately precede an epilogue code pattern. As of this writing, the
18 // SEH_Epilogue pseudo instruction takes care of that.
19 //
20 // Second, all non-tail call jump targets must be within the *half-open*
21 // interval of the bounds of the function. The unwinder distinguishes between
22 // internal jump instructions and tail calls in an epilogue sequence by checking
23 // the jump target against the function bounds from the .pdata section. This
24 // means that the last regular MBB of an LLVM function must not be empty if
25 // there are regular jumps targeting it.
26 //
27 // This pass upholds these invariants by ensuring that blocks at the end of a
28 // function or funclet are a) not empty and b) do not end in a CALL instruction.
29 //
30 // Unwinder implementation for reference:
31 // https://github.com/dotnet/coreclr/blob/a9f3fc16483eecfc47fb79c362811d870be02249/src/unwinder/amd64/unwinder_amd64.cpp#L1015
32 //
33 //===----------------------------------------------------------------------===//
34 
35 #include "X86.h"
36 #include "X86InstrInfo.h"
37 #include "X86Subtarget.h"
40 
41 #define AVOIDCALL_DESC "X86 avoid trailing call pass"
42 #define AVOIDCALL_NAME "x86-avoid-trailing-call"
43 
44 #define DEBUG_TYPE AVOIDCALL_NAME
45 
46 using namespace llvm;
47 
48 namespace {
49 class X86AvoidTrailingCallPass : public MachineFunctionPass {
50 public:
51  X86AvoidTrailingCallPass() : MachineFunctionPass(ID) {}
52 
53  bool runOnMachineFunction(MachineFunction &MF) override;
54 
55  static char ID;
56 
57 private:
58  StringRef getPassName() const override { return AVOIDCALL_DESC; }
59 };
60 } // end anonymous namespace
61 
63 
65  return new X86AvoidTrailingCallPass();
66 }
67 
68 INITIALIZE_PASS(X86AvoidTrailingCallPass, AVOIDCALL_NAME, AVOIDCALL_DESC, false, false)
69 
70 // A real instruction is a non-meta, non-pseudo instruction. Some pseudos
71 // expand to nothing, and some expand to code. This logic conservatively assumes
72 // they might expand to nothing.
74  return MI.isCall() || (!MI.isPseudo() && !MI.isMetaInstruction());
75 }
76 
77 // Return true if this is a call instruction, but not a tail call.
78 static bool isCallInstruction(const MachineInstr &MI) {
79  return MI.isCall() && !MI.isReturn();
80 }
81 
82 bool X86AvoidTrailingCallPass::runOnMachineFunction(MachineFunction &MF) {
83  const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
84  const X86InstrInfo &TII = *STI.getInstrInfo();
85  assert(STI.isTargetWin64() && "pass only runs on Win64");
86 
87  // We don't need to worry about any of the invariants described above if there
88  // is no unwind info (CFI).
89  if (!MF.hasWinCFI())
90  return false;
91 
92  // FIXME: Perhaps this pass should also replace SEH_Epilogue by inserting nops
93  // before epilogues.
94 
95  bool Changed = false;
96  for (MachineBasicBlock &MBB : MF) {
97  // Look for basic blocks that precede funclet entries or are at the end of
98  // the function.
99  MachineBasicBlock *NextMBB = MBB.getNextNode();
100  if (NextMBB && !NextMBB->isEHFuncletEntry())
101  continue;
102 
103  // Find the last real instruction in this block.
104  auto LastRealInstr = llvm::find_if(reverse(MBB), isCallOrRealInstruction);
105 
106  // If the block is empty or the last real instruction is a call instruction,
107  // insert an int3. If there is a call instruction, insert the int3 between
108  // the call and any labels or other meta instructions. If the block is
109  // empty, insert at block end.
110  bool IsEmpty = LastRealInstr == MBB.rend();
111  bool IsCall = !IsEmpty && isCallInstruction(*LastRealInstr);
112  if (IsEmpty || IsCall) {
113  LLVM_DEBUG({
114  if (IsCall) {
115  dbgs() << "inserting int3 after trailing call instruction:\n";
116  LastRealInstr->dump();
117  dbgs() << '\n';
118  } else {
119  dbgs() << "inserting int3 in trailing empty MBB:\n";
120  MBB.dump();
121  }
122  });
123 
125  DebugLoc DL;
126  if (IsCall) {
127  MBBI = std::next(LastRealInstr.getReverse());
128  DL = LastRealInstr->getDebugLoc();
129  }
130  BuildMI(MBB, MBBI, DL, TII.get(X86::INT3));
131  Changed = true;
132  }
133  }
134 
135  return Changed;
136 }
llvm::MachineFunction::hasWinCFI
bool hasWinCFI() const
Definition: MachineFunction.h:742
MI
IRTranslator LLVM IR MI
Definition: IRTranslator.cpp:109
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
llvm::AArch64PACKey::ID
ID
Definition: AArch64BaseInfo.h:818
llvm::createX86AvoidTrailingCallPass
FunctionPass * createX86AvoidTrailingCallPass()
Return a pass that inserts int3 at the end of the function if it ends with a CALL instruction.
Definition: X86AvoidTrailingCall.cpp:64
X86Subtarget.h
llvm::X86Subtarget::getInstrInfo
const X86InstrInfo * getInstrInfo() const override
Definition: X86Subtarget.h:128
llvm::MachineBasicBlock::isEHFuncletEntry
bool isEHFuncletEntry() const
Returns true if this is the entry block of an EH funclet.
Definition: MachineBasicBlock.h:606
llvm::ilist_node_with_parent::getNextNode
NodeTy * getNextNode()
Get the next node, or nullptr for the list tail.
Definition: ilist_node.h:289
llvm::X86Subtarget
Definition: X86Subtarget.h:52
llvm::MachineFunctionPass
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
Definition: MachineFunctionPass.h:30
isCallInstruction
static bool isCallInstruction(const MachineInstr &MI)
Definition: X86AvoidTrailingCall.cpp:78
llvm::X86Subtarget::isTargetWin64
bool isTargetWin64() const
Definition: X86Subtarget.h:315
LLVM_DEBUG
#define LLVM_DEBUG(X)
Definition: Debug.h:101
llvm::MachineBasicBlock::dump
void dump() const
Definition: MachineBasicBlock.cpp:292
llvm::dbgs
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
X86.h
INITIALIZE_PASS
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:37
TII
const HexagonInstrInfo * TII
Definition: HexagonCopyToCombine.cpp:125
llvm::MachineBasicBlock::rend
reverse_iterator rend()
Definition: MachineBasicBlock.h:319
llvm::CallingConv::ID
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
llvm::MachineBasicBlock
Definition: MachineBasicBlock.h:94
llvm::MachineFunction::getSubtarget
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
Definition: MachineFunction.h:660
llvm::MachineInstr
Representation of each machine instruction.
Definition: MachineInstr.h:66
MachineFunctionPass.h
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
AVOIDCALL_NAME
#define AVOIDCALL_NAME
Definition: X86AvoidTrailingCall.cpp:42
llvm::MachineFunction
Definition: MachineFunction.h:257
llvm::X86InstrInfo
Definition: X86InstrInfo.h:138
llvm::StringRef
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
MBBI
MachineBasicBlock MachineBasicBlock::iterator MBBI
Definition: AArch64SLSHardening.cpp:75
DL
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Definition: AArch64SLSHardening.cpp:76
llvm::find_if
auto find_if(R &&Range, UnaryPredicate P)
Provide wrappers to std::find_if which take ranges instead of having to pass begin/end explicitly.
Definition: STLExtras.h:1761
MBB
MachineBasicBlock & MBB
Definition: AArch64SLSHardening.cpp:74
llvm::BuildMI
MachineInstrBuilder BuildMI(MachineFunction &MF, const MIMetadata &MIMD, const MCInstrDesc &MCID)
Builder interface. Specify how to create the initial instruction itself.
Definition: MachineInstrBuilder.h:357
MachineInstrBuilder.h
isCallOrRealInstruction
static bool isCallOrRealInstruction(MachineInstr &MI)
Definition: X86AvoidTrailingCall.cpp:73
llvm::reverse
auto reverse(ContainerTy &&C)
Definition: STLExtras.h:485
llvm::FunctionPass
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:308
llvm::DebugLoc
A debug info location.
Definition: DebugLoc.h:33
X86InstrInfo.h
llvm::MachineInstrBundleIterator< MachineInstr >
AVOIDCALL_DESC
#define AVOIDCALL_DESC
Definition: X86AvoidTrailingCall.cpp:41
llvm::MachineBasicBlock::end
iterator end()
Definition: MachineBasicBlock.h:311