forked from OSchip/llvm-project
109 lines
3.6 KiB
C++
109 lines
3.6 KiB
C++
//===----- X86AvoidTrailingCall.cpp - Insert int3 after trailing calls ----===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// The Windows x64 unwinder has trouble unwinding the stack when a return
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// address points to the end of the function. This pass maintains the invariant
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// that every return address is inside the bounds of its parent function or
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// funclet by inserting int3 if the last instruction would otherwise be a call.
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//
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//===----------------------------------------------------------------------===//
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#include "X86.h"
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#include "X86InstrInfo.h"
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#include "X86Subtarget.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#define DEBUG_TYPE "x86-avoid-trailing-call"
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using namespace llvm;
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namespace {
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class X86AvoidTrailingCallPass : public MachineFunctionPass {
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public:
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X86AvoidTrailingCallPass() : MachineFunctionPass(ID) {}
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bool runOnMachineFunction(MachineFunction &MF) override;
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private:
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StringRef getPassName() const override {
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return "X86 avoid trailing call pass";
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}
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static char ID;
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};
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char X86AvoidTrailingCallPass::ID = 0;
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} // end anonymous namespace
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FunctionPass *llvm::createX86AvoidTrailingCallPass() {
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return new X86AvoidTrailingCallPass();
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}
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// A real instruction is a non-meta, non-pseudo instruction. Some pseudos
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// expand to nothing, and some expand to code. This logic conservatively assumes
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// they might expand to nothing.
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static bool isRealInstruction(MachineInstr &MI) {
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return !MI.isPseudo() && !MI.isMetaInstruction();
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}
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// Return true if this is a call instruction, but not a tail call.
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static bool isCallInstruction(const MachineInstr &MI) {
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return MI.isCall() && !MI.isReturn();
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}
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bool X86AvoidTrailingCallPass::runOnMachineFunction(MachineFunction &MF) {
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const X86Subtarget &STI = MF.getSubtarget<X86Subtarget>();
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const X86InstrInfo &TII = *STI.getInstrInfo();
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assert(STI.isTargetWin64() && "pass only runs on Win64");
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// FIXME: Perhaps this pass should also replace SEH_Epilogue by inserting nops
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// before epilogues.
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bool Changed = false;
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for (MachineBasicBlock &MBB : MF) {
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// Look for basic blocks that precede funclet entries or are at the end of
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// the function.
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MachineBasicBlock *NextMBB = MBB.getNextNode();
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if (NextMBB && !NextMBB->isEHFuncletEntry())
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continue;
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// Find the last real instruction in this block, or previous blocks if this
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// block is empty.
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MachineBasicBlock::reverse_iterator LastRealInstr;
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for (MachineBasicBlock &RMBB :
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make_range(MBB.getReverseIterator(), MF.rend())) {
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LastRealInstr = llvm::find_if(reverse(RMBB), isRealInstruction);
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if (LastRealInstr != RMBB.rend())
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break;
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}
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// Do nothing if this function or funclet has no instructions.
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if (LastRealInstr == MF.begin()->rend())
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continue;
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// If this is a call instruction, insert int3 right after it with the same
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// DebugLoc. Convert back to a forward iterator and advance the insertion
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// position once.
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if (isCallInstruction(*LastRealInstr)) {
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LLVM_DEBUG({
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dbgs() << "inserting int3 after trailing call instruction:\n";
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LastRealInstr->dump();
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dbgs() << '\n';
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});
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MachineBasicBlock::iterator MBBI = std::next(LastRealInstr.getReverse());
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BuildMI(*LastRealInstr->getParent(), MBBI, LastRealInstr->getDebugLoc(),
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TII.get(X86::INT3));
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Changed = true;
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}
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}
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return Changed;
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}
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