98 lines
3.1 KiB
C++
98 lines
3.1 KiB
C++
//===-- MipsNaClELFStreamer.cpp - ELF Object Output for Mips NaCl ---------===//
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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 MCELFStreamer for Mips NaCl. It emits .o object files
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// as required by NaCl's SFI sandbox. It inserts address-masking instructions
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// before dangerous control-flow instructions. It aligns on bundle size all
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// functions and all targets of indirect branches.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "mips-mc-nacl"
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#include "Mips.h"
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#include "MipsMCNaCl.h"
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#include "llvm/MC/MCELFStreamer.h"
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using namespace llvm;
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namespace {
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const unsigned IndirectBranchMaskReg = Mips::T6;
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/// Extend the generic MCELFStreamer class so that it can mask dangerous
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/// instructions.
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class MipsNaClELFStreamer : public MCELFStreamer {
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public:
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MipsNaClELFStreamer(MCContext &Context, MCAsmBackend &TAB, raw_ostream &OS,
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MCCodeEmitter *Emitter)
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: MCELFStreamer(Context, TAB, OS, Emitter) {}
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~MipsNaClELFStreamer() {}
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private:
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bool isIndirectJump(const MCInst &MI) {
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return MI.getOpcode() == Mips::JR || MI.getOpcode() == Mips::RET;
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}
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void emitMask(unsigned AddrReg, unsigned MaskReg,
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const MCSubtargetInfo &STI) {
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MCInst MaskInst;
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MaskInst.setOpcode(Mips::AND);
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MaskInst.addOperand(MCOperand::CreateReg(AddrReg));
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MaskInst.addOperand(MCOperand::CreateReg(AddrReg));
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MaskInst.addOperand(MCOperand::CreateReg(MaskReg));
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MCELFStreamer::EmitInstruction(MaskInst, STI);
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}
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// Sandbox indirect branch or return instruction by inserting mask operation
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// before it.
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void sandboxIndirectJump(const MCInst &MI, const MCSubtargetInfo &STI) {
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unsigned AddrReg = MI.getOperand(0).getReg();
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EmitBundleLock(false);
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emitMask(AddrReg, IndirectBranchMaskReg, STI);
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MCELFStreamer::EmitInstruction(MI, STI);
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EmitBundleUnlock();
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}
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public:
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/// This function is the one used to emit instruction data into the ELF
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/// streamer. We override it to mask dangerous instructions.
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virtual void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI) {
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if (isIndirectJump(Inst))
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sandboxIndirectJump(Inst, STI);
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else
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MCELFStreamer::EmitInstruction(Inst, STI);
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}
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};
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} // end anonymous namespace
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namespace llvm {
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MCELFStreamer *createMipsNaClELFStreamer(MCContext &Context, MCAsmBackend &TAB,
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raw_ostream &OS,
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MCCodeEmitter *Emitter, bool RelaxAll,
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bool NoExecStack) {
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MipsNaClELFStreamer *S = new MipsNaClELFStreamer(Context, TAB, OS, Emitter);
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if (RelaxAll)
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S->getAssembler().setRelaxAll(true);
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if (NoExecStack)
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S->getAssembler().setNoExecStack(true);
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// Set bundle-alignment as required by the NaCl ABI for the target.
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S->EmitBundleAlignMode(MIPS_NACL_BUNDLE_ALIGN);
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return S;
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}
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}
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