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/BPFMCFixups.h"
10 #include "MCTargetDesc/BPFMCTargetDesc.h"
11 #include "llvm/ADT/StringRef.h"
12 #include "llvm/MC/MCAsmBackend.h"
13 #include "llvm/MC/MCAssembler.h"
14 #include "llvm/MC/MCContext.h"
15 #include "llvm/MC/MCFixup.h"
16 #include "llvm/MC/MCFixupKindInfo.h"
17 #include "llvm/MC/MCObjectWriter.h"
18 #include "llvm/Support/EndianStream.h"
19 #include <cassert>
20 #include <cstdint>
21 
22 using namespace llvm;
23 
24 namespace {
25 
26 class BPFAsmBackend : public MCAsmBackend {
27 public:
28   BPFAsmBackend(llvm::endianness Endian) : MCAsmBackend(Endian) {}
29   ~BPFAsmBackend() override = default;
30 
31   void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
32                   const MCValue &Target, MutableArrayRef<char> Data,
33                   uint64_t Value, bool IsResolved,
34                   const MCSubtargetInfo *STI) const override;
35 
36   std::unique_ptr<MCObjectTargetWriter>
37   createObjectTargetWriter() const override;
38 
39   // No instruction requires relaxation
40   bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
41                             const MCRelaxableFragment *DF,
42                             const MCAsmLayout &Layout) const override {
43     return false;
44   }
45 
46   unsigned getNumFixupKinds() const override {
47     return BPF::NumTargetFixupKinds;
48   }
49   const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
50 
51   bool writeNopData(raw_ostream &OS, uint64_t Count,
52                     const MCSubtargetInfo *STI) const override;
53 };
54 
55 } // end anonymous namespace
56 
57 const MCFixupKindInfo &
58 BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
59   const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = {
60     { "FK_BPF_PCRel_4",  0, 32, MCFixupKindInfo::FKF_IsPCRel },
61   };
62 
63   if (Kind < FirstTargetFixupKind)
64     return MCAsmBackend::getFixupKindInfo(Kind);
65 
66   assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
67          "Invalid kind!");
68   return Infos[Kind - FirstTargetFixupKind];
69 }
70 
71 bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
72                                  const MCSubtargetInfo *STI) const {
73   if ((Count % 8) != 0)
74     return false;
75 
76   for (uint64_t i = 0; i < Count; i += 8)
77     support::endian::write<uint64_t>(OS, 0x15000000, Endian);
78 
79   return true;
80 }
81 
82 void BPFAsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
83                                const MCValue &Target,
84                                MutableArrayRef<char> Data, uint64_t Value,
85                                bool IsResolved,
86                                const MCSubtargetInfo *STI) const {
87   if (Fixup.getKind() == FK_SecRel_8) {
88     // The Value is 0 for global variables, and the in-section offset
89     // for static variables. Write to the immediate field of the inst.
90     assert(Value <= UINT32_MAX);
91     support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4],
92                                      static_cast<uint32_t>(Value),
93                                      Endian);
94   } else if (Fixup.getKind() == FK_Data_4) {
95     support::endian::write<uint32_t>(&Data[Fixup.getOffset()], Value, Endian);
96   } else if (Fixup.getKind() == FK_Data_8) {
97     support::endian::write<uint64_t>(&Data[Fixup.getOffset()], Value, Endian);
98   } else if (Fixup.getKind() == FK_PCRel_4) {
99     Value = (uint32_t)((Value - 8) / 8);
100     if (Endian == llvm::endianness::little) {
101       Data[Fixup.getOffset() + 1] = 0x10;
102       support::endian::write32le(&Data[Fixup.getOffset() + 4], Value);
103     } else {
104       Data[Fixup.getOffset() + 1] = 0x1;
105       support::endian::write32be(&Data[Fixup.getOffset() + 4], Value);
106     }
107   } else if (Fixup.getTargetKind() == BPF::FK_BPF_PCRel_4) {
108     // The input Value represents the number of bytes.
109     Value = (uint32_t)((Value - 8) / 8);
110     support::endian::write<uint32_t>(&Data[Fixup.getOffset() + 4], Value,
111                                      Endian);
112   } else {
113     assert(Fixup.getKind() == FK_PCRel_2);
114 
115     int64_t ByteOff = (int64_t)Value - 8;
116     if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8)
117       report_fatal_error("Branch target out of insn range");
118 
119     Value = (uint16_t)((Value - 8) / 8);
120     support::endian::write<uint16_t>(&Data[Fixup.getOffset() + 2], Value,
121                                      Endian);
122   }
123 }
124 
125 std::unique_ptr<MCObjectTargetWriter>
126 BPFAsmBackend::createObjectTargetWriter() const {
127   return createBPFELFObjectWriter(0);
128 }
129 
130 MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
131                                         const MCSubtargetInfo &STI,
132                                         const MCRegisterInfo &MRI,
133                                         const MCTargetOptions &) {
134   return new BPFAsmBackend(llvm::endianness::little);
135 }
136 
137 MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
138                                           const MCSubtargetInfo &STI,
139                                           const MCRegisterInfo &MRI,
140                                           const MCTargetOptions &) {
141   return new BPFAsmBackend(llvm::endianness::big);
142 }
143