1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
| //===----- X86AvoidTrailingCall.cpp - Insert int3 after trailing calls ----===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The Windows x64 unwinder has trouble unwinding the stack when a return
// address points to the end of the function. This pass maintains the invariant
// that every return address is inside the bounds of its parent function or
// funclet by inserting int3 if the last instruction would otherwise be a call.
//
//===----------------------------------------------------------------------===//
#include "X86.h"
#include "X86InstrInfo.h"
#include "X86Subtarget.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#define DEBUG_TYPE "x86-avoid-trailing-call"
using namespace llvm;
namespace {
class X86AvoidTrailingCallPass : public MachineFunctionPass {
public:
X86AvoidTrailingCallPass() : MachineFunctionPass(ID) {}
bool runOnMachineFunction(MachineFunction &MF) override;
private:
StringRef getPassName() const override {
return "X86 avoid trailing call pass";
}
static char ID;
};
char X86AvoidTrailingCallPass::ID = 0;
} // end anonymous namespace
FunctionPass *llvm::createX86AvoidTrailingCallPass() {
return new X86AvoidTrailingCallPass();
}
// A real instruction is a non-meta, non-pseudo instruction. Some pseudos
// expand to nothing, and some expand to code. This logic conservatively assumes
// they might expand to nothing.
static bool isRealInstruction(MachineInstr &MI) {
return !MI.isPseudo() && !MI.isMetaInstruction();
}
// Return true if this is a call instruction, but not a tail call.
static bool isCallInstruction(const MachineInstr &MI) {
return MI.isCall() && !MI.isReturn();
}
bool X86AvoidTrailingCallPass::runOnMachineFunction(MachineFunction &MF) {
const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
const X86InstrInfo &TII = *STI.getInstrInfo();
assert(STI.isTargetWin64() && "pass only runs on Win64");
// FIXME: Perhaps this pass should also replace SEH_Epilogue by inserting nops
// before epilogues.
bool Changed = false;
for (MachineBasicBlock &MBB : MF) {
// Look for basic blocks that precede funclet entries or are at the end of
// the function.
MachineBasicBlock *NextMBB = MBB.getNextNode();
if (NextMBB && !NextMBB->isEHFuncletEntry())
continue;
// Find the last real instruction in this block, or previous blocks if this
// block is empty.
MachineBasicBlock::reverse_iterator LastRealInstr;
for (MachineBasicBlock &RMBB :
make_range(MBB.getReverseIterator(), MF.rend())) {
LastRealInstr = llvm::find_if(reverse(RMBB), isRealInstruction);
if (LastRealInstr != RMBB.rend())
break;
}
// Do nothing if this function or funclet has no instructions.
if (LastRealInstr == MF.begin()->rend())
continue;
// If this is a call instruction, insert int3 right after it with the same
// DebugLoc. Convert back to a forward iterator and advance the insertion
// position once.
if (isCallInstruction(*LastRealInstr)) {
LLVM_DEBUG({
dbgs() << "inserting int3 after trailing call instruction:\n";
LastRealInstr->dump();
dbgs() << '\n';
});
MachineBasicBlock::iterator MBBI = std::next(LastRealInstr.getReverse());
BuildMI(*LastRealInstr->getParent(), MBBI, LastRealInstr->getDebugLoc(),
TII.get(X86::INT3));
Changed = true;
}
}
return Changed;
}
|