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/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/MCFixupKindInfo.h"
16#include "llvm/MC/MCObjectWriter.h"
17#include "llvm/Support/EndianStream.h"
18#include <cassert>
19#include <cstdint>
20
21using namespace llvm;
22
23namespace {
24
25class BPFAsmBackend : public MCAsmBackend {
26public:
27 BPFAsmBackend(llvm::endianness Endian) : MCAsmBackend(Endian) {}
28 ~BPFAsmBackend() override = default;
29
30 void applyFixup(const MCFragment &, const MCFixup &, const MCValue &Target,
31 MutableArrayRef<char> Data, uint64_t Value,
32 bool IsResolved) override;
33
34 std::unique_ptr<MCObjectTargetWriter>
35 createObjectTargetWriter() const override;
36
37 MCFixupKindInfo getFixupKindInfo(MCFixupKind Kind) const override;
38
39 bool writeNopData(raw_ostream &OS, uint64_t Count,
40 const MCSubtargetInfo *STI) const override;
41};
42
43} // end anonymous namespace
44
45MCFixupKindInfo BPFAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
46 const static MCFixupKindInfo Infos[BPF::NumTargetFixupKinds] = {
47 { .Name: "FK_BPF_PCRel_4", .TargetOffset: 0, .TargetSize: 32, .Flags: MCFixupKindInfo::FKF_IsPCRel },
48 };
49
50 if (Kind < FirstTargetFixupKind)
51 return MCAsmBackend::getFixupKindInfo(Kind);
52
53 assert(unsigned(Kind - FirstTargetFixupKind) < BPF::NumTargetFixupKinds &&
54 "Invalid kind!");
55 return Infos[Kind - FirstTargetFixupKind];
56}
57
58bool BPFAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count,
59 const MCSubtargetInfo *STI) 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&: OS, value: 0x15000000, endian: Endian);
65
66 return true;
67}
68
69void BPFAsmBackend::applyFixup(const MCFragment &F, const MCFixup &Fixup,
70 const MCValue &Target,
71 MutableArrayRef<char> Data, uint64_t Value,
72 bool IsResolved) {
73 maybeAddReloc(F, Fixup, Target, Value, IsResolved);
74 if (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>(memory: &Data[Fixup.getOffset() + 4],
79 value: static_cast<uint32_t>(Value),
80 endian: Endian);
81 } else if (Fixup.getKind() == FK_Data_4) {
82 support::endian::write<uint32_t>(memory: &Data[Fixup.getOffset()], value: Value, endian: Endian);
83 } else if (Fixup.getKind() == FK_Data_8) {
84 support::endian::write<uint64_t>(memory: &Data[Fixup.getOffset()], value: Value, endian: Endian);
85 } else if (Fixup.getKind() == FK_PCRel_4) {
86 Value = (uint32_t)((Value - 8) / 8);
87 if (Endian == llvm::endianness::little) {
88 Data[Fixup.getOffset() + 1] = 0x10;
89 support::endian::write32le(P: &Data[Fixup.getOffset() + 4], V: Value);
90 } else {
91 Data[Fixup.getOffset() + 1] = 0x1;
92 support::endian::write32be(P: &Data[Fixup.getOffset() + 4], V: Value);
93 }
94 } else if (Fixup.getTargetKind() == BPF::FK_BPF_PCRel_4) {
95 // The input Value represents the number of bytes.
96 Value = (uint32_t)((Value - 8) / 8);
97 support::endian::write<uint32_t>(memory: &Data[Fixup.getOffset() + 4], value: Value,
98 endian: Endian);
99 } else {
100 assert(Fixup.getKind() == FK_PCRel_2);
101
102 int64_t ByteOff = (int64_t)Value - 8;
103 if (ByteOff > INT16_MAX * 8 || ByteOff < INT16_MIN * 8)
104 report_fatal_error(reason: "Branch target out of insn range");
105
106 Value = (uint16_t)((Value - 8) / 8);
107 support::endian::write<uint16_t>(memory: &Data[Fixup.getOffset() + 2], value: Value,
108 endian: Endian);
109 }
110}
111
112std::unique_ptr<MCObjectTargetWriter>
113BPFAsmBackend::createObjectTargetWriter() const {
114 return createBPFELFObjectWriter(OSABI: 0);
115}
116
117MCAsmBackend *llvm::createBPFAsmBackend(const Target &T,
118 const MCSubtargetInfo &STI,
119 const MCRegisterInfo &MRI,
120 const MCTargetOptions &) {
121 return new BPFAsmBackend(llvm::endianness::little);
122}
123
124MCAsmBackend *llvm::createBPFbeAsmBackend(const Target &T,
125 const MCSubtargetInfo &STI,
126 const MCRegisterInfo &MRI,
127 const MCTargetOptions &) {
128 return new BPFAsmBackend(llvm::endianness::big);
129}
130