lib/Target/BPF/MCTargetDesc/BPFAsmBackend.cpp

   1 //===-- BPFAsmBackend.cpp - BPF Assembler Backend -------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "MCTargetDesc/BPFMCTargetDesc.h"
  10 #include "llvm/ADT/StringRef.h"
  11 #include "llvm/MC/MCAsmBackend.h"
  12 #include "llvm/MC/MCAssembler.h"
  13 #include "llvm/MC/MCContext.h"
  14 #include "llvm/MC/MCFixup.h"
  15 #include "llvm/MC/MCObjectWriter.h"
  16 #include "llvm/Support/EndianStream.h"
  17 #include <cassert>
  18 #include <cstdint>
  19
  20 using namespace llvm;
  21
  22 namespace {
  23
  24 class BPFAsmBackend : public MCAsmBackend {
  25 public:
  26   BPFAsmBackend(support::endianness Endian) : MCAsmBackend(Endian) {}
  27   ~BPFAsmBackend() override = default;
  28
  29   void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
  30                   const MCValue &Target, MutableArrayRef<char> Data,
  31                   uint64_t Value, bool IsResolved,
  32                   const MCSubtargetInfo *STI) const override;
  33
  34   std::unique_ptr<MCObjectTargetWriter>
  35   createObjectTargetWriter() const override;
  36
  37   // No instruction requires relaxation
  38   bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
  39                             const MCRelaxableFragment *DF,
  40                             const MCAsmLayout &Layout) const override {
  41     return false;
  42   }
  43
  44   unsigned getNumFixupKinds() const override { return 1; }
  45
  46   bool mayNeedRelaxation(const MCInst &Inst,
  47                          const MCSubtargetInfo &STI) const override {
  48     return false;
  49   }
  50
  51   void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
  52                         MCInst &Res) const override {}
  53
  54   bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
  55 };
  56
  57 } // end anonymous namespace
  58
  59 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
  60   if ((Count % 8) != 0)
  61     return false;
  62
  63   for (uint64_t i = 0; i < Count; i += 8)
  64     support::endian::write<uint64_t>(OS, 0x15000000, Endian);
  65
  66   return true;
  67 }
  68
  69 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
  70                                const MCValue &Target,
  71                                MutableArrayRef<char> Data, uint64_t Value,
  72                                bool IsResolved,
  73                                const MCSubtargetInfo *STI) const {
  74   if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
  75     // The Value is 0 for global variables, and the in-section offset
  76     // for static variables. Write to the immediate field of the inst.
  77     assert(Value <= UINT32_MAX);
  78     support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
  79                                      static_cast<uint32_t>(Value),
  80                                      Endian);
  81   } else if (Fixup.getKind() == FK_Data_4) {
  82     support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
  83   } else if (Fixup.getKind() == FK_Data_8) {
  84     support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
  85   } else if (Fixup.getKind() == FK_PCRel_4) {
  86     Value = (uint32_t)((Value - 8) / 8);
  87     if (Endian == support::little) {
  88       Data[Fixup.getOffset() + 1] = 0x10;
  89       support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
  90     } else {
  91       Data[Fixup.getOffset() + 1] = 0x1;
  92       support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
  93     }
  94   } else {
  95     assert(Fixup.getKind() == FK_PCRel_2);
  96     Value = (uint16_t)((Value - 8) / 8);
  97     support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
  98                                      Endian);
  99   }
 100 }
 101
 102 std::unique_ptr<MCObjectTargetWriter>
 103 BPFAsmBackend::createObjectTargetWriter() const {
 104   return createBPFELFObjectWriter(0);
 105 }
 106
 107 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
 108                                         const MCSubtargetInfo &STI,
 109                                         const MCRegisterInfo &MRI,
 110                                         const MCTargetOptions &) {
 111   return new BPFAsmBackend(support::little);
 112 }
 113
 114 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
 115                                           const MCSubtargetInfo &STI,
 116                                           const MCRegisterInfo &MRI,
 117                                           const MCTargetOptions &) {
 118   return new BPFAsmBackend(support::big);
 119 }