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3f3438a596
This patch fixes crashes related with how PatchableFunction selects the instruction to make patchable: - Ensure PatchableFunction skips all instructions that don't generate actual machine instructions. - Handle the case where the first MachineBasicBlock is empty - Removed support for 16 bit x86 architectures. Note: another issue remains related with PatchableFunction, in the lowering part. See https://github.com/llvm/llvm-project/issues/59039 Differential Revision: https://reviews.llvm.org/D137642
99 lines
3.6 KiB
C++
99 lines
3.6 KiB
C++
//===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
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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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// This file implements edits function bodies in place to support the
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// "patchable-function" attribute.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/MachineFunction.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/CodeGen/MachineInstrBuilder.h"
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#include "llvm/CodeGen/TargetInstrInfo.h"
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#include "llvm/CodeGen/TargetSubtargetInfo.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/PassRegistry.h"
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using namespace llvm;
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namespace {
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struct PatchableFunction : public MachineFunctionPass {
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static char ID; // Pass identification, replacement for typeid
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PatchableFunction() : MachineFunctionPass(ID) {
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initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
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}
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bool runOnMachineFunction(MachineFunction &F) override;
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MachineFunctionProperties getRequiredProperties() const override {
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return MachineFunctionProperties().set(
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MachineFunctionProperties::Property::NoVRegs);
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}
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};
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}
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bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
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if (MF.getFunction().hasFnAttribute("patchable-function-entry")) {
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MachineBasicBlock &FirstMBB = *MF.begin();
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const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
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// The initial .loc covers PATCHABLE_FUNCTION_ENTER.
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BuildMI(FirstMBB, FirstMBB.begin(), DebugLoc(),
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TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
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return true;
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}
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if (!MF.getFunction().hasFnAttribute("patchable-function"))
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return false;
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#ifndef NDEBUG
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Attribute PatchAttr = MF.getFunction().getFnAttribute("patchable-function");
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StringRef PatchType = PatchAttr.getValueAsString();
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assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
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#endif
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auto &FirstMBB = *MF.begin();
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auto *TII = MF.getSubtarget().getInstrInfo();
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MachineBasicBlock::iterator FirstActualI = llvm::find_if(
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FirstMBB, [](const MachineInstr &MI) { return !MI.isMetaInstruction(); });
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if (FirstActualI == FirstMBB.end()) {
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// As of Microsoft documentation on /hotpatch feature, we must ensure that
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// "the first instruction of each function is at least two bytes, and no
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// jump within the function goes to the first instruction"
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// When the first MBB is empty, insert a patchable no-op. This ensures the
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// first instruction is patchable in two special cases:
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// - the function is empty (e.g. unreachable)
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// - the function jumps back to the first instruction, which is in a
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// successor MBB.
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BuildMI(&FirstMBB, DebugLoc(), TII->get(TargetOpcode::PATCHABLE_OP))
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.addImm(2)
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.addImm(TargetOpcode::PATCHABLE_OP);
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MF.ensureAlignment(Align(16));
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return true;
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}
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auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
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TII->get(TargetOpcode::PATCHABLE_OP))
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.addImm(2)
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.addImm(FirstActualI->getOpcode());
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for (auto &MO : FirstActualI->operands())
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MIB.add(MO);
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FirstActualI->eraseFromParent();
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MF.ensureAlignment(Align(16));
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return true;
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}
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char PatchableFunction::ID = 0;
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char &llvm::PatchableFunctionID = PatchableFunction::ID;
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INITIALIZE_PASS(PatchableFunction, "patchable-function",
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"Implement the 'patchable-function' attribute", false, false)
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