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151328540e
Summary: The `"patchable-function"` attribute can be used by an LLVM client to influence LLVM's code generation in ways that makes the generated code easily patchable at runtime (for instance, to redirect control). Right now only one patchability scheme is supported, `"prologue-short-redirect"`, but this can be expanded in the future. Reviewers: joker.eph, rnk, echristo, dberris Subscribers: joker.eph, echristo, mcrosier, llvm-commits Differential Revision: http://reviews.llvm.org/D19046 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266715 91177308-0d34-0410-b5e6-96231b3b80d8
71 lines
2.3 KiB
C++
71 lines
2.3 KiB
C++
//===-- PatchableFunction.cpp - Patchable prologues for LLVM -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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/Passes.h"
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#include "llvm/CodeGen/Analysis.h"
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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/Target/TargetFrameLowering.h"
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#include "llvm/Target/TargetInstrInfo.h"
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#include "llvm/Target/TargetSubtargetInfo.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::AllVRegsAllocated);
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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"))
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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 &FirstMI = *FirstMBB.begin();
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auto *TII = MF.getSubtarget().getInstrInfo();
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auto MIB = BuildMI(FirstMBB, FirstMBB.begin(), FirstMI.getDebugLoc(),
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TII->get(TargetOpcode::PATCHABLE_OP))
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.addImm(2)
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.addImm(FirstMI.getOpcode());
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for (auto &MO : FirstMI.operands())
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MIB.addOperand(MO);
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FirstMI.eraseFromParent();
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MF.ensureAlignment(4);
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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", "", false, false)
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