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 writeNopData(raw_ostream &OS, uint64_t Count) const override;
47 };
48 
49 } // end anonymous namespace
50 
51 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
52   if ((Count % 8) != 0)
53     return false;
54 
55   for (uint64_t i = 0; i < Count; i += 8)
56     support::endian::write<uint64_t>(OS, 0x15000000, Endian);
57 
58   return true;
59 }
60 
61 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
62                                const MCValue &Target,
63                                MutableArrayRef<char> Data, uint64_t Value,
64                                bool IsResolved,
65                                const MCSubtargetInfo *STI) const {
66   if (Fixup.getKind() == FK_SecRel_4 || Fixup.getKind() == FK_SecRel_8) {
67     // The Value is 0 for global variables, and the in-section offset
68     // for static variables. Write to the immediate field of the inst.
69     assert(Value <= UINT32_MAX);
70     support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
71                                      static_cast<uint32_t>(Value),
72                                      Endian);
73   } else if (Fixup.getKind() == FK_Data_4) {
74     support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
75   } else if (Fixup.getKind() == FK_Data_8) {
76     support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
77   } else if (Fixup.getKind() == FK_PCRel_4) {
78     Value = (uint32_t)((Value - 8) / 8);
79     if (Endian == support::little) {
80       Data[Fixup.getOffset() + 1] = 0x10;
81       support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
82     } else {
83       Data[Fixup.getOffset() + 1] = 0x1;
84       support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
85     }
86   } else {
87     assert(Fixup.getKind() == FK_PCRel_2);
88     Value = (uint16_t)((Value - 8) / 8);
89     support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
90                                      Endian);
91   }
92 }
93 
94 std::unique_ptr<MCObjectTargetWriter>
95 BPFAsmBackend::createObjectTargetWriter() const {
96   return createBPFELFObjectWriter(0);
97 }
98 
99 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
100                                         const MCSubtargetInfo &STI,
101                                         const MCRegisterInfo &MRI,
102                                         const MCTargetOptions &) {
103   return new BPFAsmBackend(support::little);
104 }
105 
106 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
107                                           const MCSubtargetInfo &STI,
108                                           const MCRegisterInfo &MRI,
109                                           const MCTargetOptions &) {
110   return new BPFAsmBackend(support::big);
111 }
112