699 lines
20 KiB
Go
699 lines
20 KiB
Go
package ebpf
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import (
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"bytes"
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"debug/elf"
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"encoding/binary"
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"io"
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"math"
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"os"
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"strings"
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"github.com/cilium/ebpf/asm"
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"github.com/cilium/ebpf/internal"
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"github.com/cilium/ebpf/internal/btf"
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"github.com/cilium/ebpf/internal/unix"
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"golang.org/x/xerrors"
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)
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type elfCode struct {
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*elf.File
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symbols []elf.Symbol
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symbolsPerSection map[elf.SectionIndex]map[uint64]elf.Symbol
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license string
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version uint32
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}
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// LoadCollectionSpec parses an ELF file into a CollectionSpec.
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func LoadCollectionSpec(file string) (*CollectionSpec, error) {
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f, err := os.Open(file)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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spec, err := LoadCollectionSpecFromReader(f)
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if err != nil {
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return nil, xerrors.Errorf("file %s: %w", file, err)
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}
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return spec, nil
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}
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// LoadCollectionSpecFromReader parses an ELF file into a CollectionSpec.
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func LoadCollectionSpecFromReader(rd io.ReaderAt) (*CollectionSpec, error) {
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f, err := elf.NewFile(rd)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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symbols, err := f.Symbols()
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if err != nil {
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return nil, xerrors.Errorf("load symbols: %v", err)
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}
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ec := &elfCode{f, symbols, symbolsPerSection(symbols), "", 0}
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var (
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licenseSection *elf.Section
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versionSection *elf.Section
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btfMaps = make(map[elf.SectionIndex]*elf.Section)
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progSections = make(map[elf.SectionIndex]*elf.Section)
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relSections = make(map[elf.SectionIndex]*elf.Section)
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mapSections = make(map[elf.SectionIndex]*elf.Section)
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dataSections = make(map[elf.SectionIndex]*elf.Section)
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)
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for i, sec := range ec.Sections {
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switch {
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case strings.HasPrefix(sec.Name, "license"):
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licenseSection = sec
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case strings.HasPrefix(sec.Name, "version"):
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versionSection = sec
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case strings.HasPrefix(sec.Name, "maps"):
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mapSections[elf.SectionIndex(i)] = sec
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case sec.Name == ".maps":
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btfMaps[elf.SectionIndex(i)] = sec
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case sec.Name == ".bss" || sec.Name == ".rodata" || sec.Name == ".data":
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dataSections[elf.SectionIndex(i)] = sec
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case sec.Type == elf.SHT_REL:
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if int(sec.Info) >= len(ec.Sections) {
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return nil, xerrors.Errorf("found relocation section %v for missing section %v", i, sec.Info)
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}
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// Store relocations under the section index of the target
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idx := elf.SectionIndex(sec.Info)
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if relSections[idx] != nil {
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return nil, xerrors.Errorf("section %d has multiple relocation sections", sec.Info)
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}
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relSections[idx] = sec
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case sec.Type == elf.SHT_PROGBITS && (sec.Flags&elf.SHF_EXECINSTR) != 0 && sec.Size > 0:
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progSections[elf.SectionIndex(i)] = sec
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}
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}
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ec.license, err = loadLicense(licenseSection)
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if err != nil {
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return nil, xerrors.Errorf("load license: %w", err)
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}
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ec.version, err = loadVersion(versionSection, ec.ByteOrder)
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if err != nil {
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return nil, xerrors.Errorf("load version: %w", err)
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}
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btfSpec, err := btf.LoadSpecFromReader(rd)
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if err != nil {
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return nil, xerrors.Errorf("load BTF: %w", err)
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}
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maps := make(map[string]*MapSpec)
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if err := ec.loadMaps(maps, mapSections); err != nil {
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return nil, xerrors.Errorf("load maps: %w", err)
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}
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if len(btfMaps) > 0 {
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if err := ec.loadBTFMaps(maps, btfMaps, btfSpec); err != nil {
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return nil, xerrors.Errorf("load BTF maps: %w", err)
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}
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}
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if len(dataSections) > 0 {
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if err := ec.loadDataSections(maps, dataSections, btfSpec); err != nil {
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return nil, xerrors.Errorf("load data sections: %w", err)
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}
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}
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relocations, err := ec.loadRelocations(relSections)
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if err != nil {
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return nil, xerrors.Errorf("load relocations: %w", err)
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}
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progs, err := ec.loadPrograms(progSections, relocations, btfSpec)
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if err != nil {
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return nil, xerrors.Errorf("load programs: %w", err)
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}
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return &CollectionSpec{maps, progs}, nil
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}
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func loadLicense(sec *elf.Section) (string, error) {
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if sec == nil {
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return "", xerrors.New("missing license section")
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}
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data, err := sec.Data()
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if err != nil {
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return "", xerrors.Errorf("section %s: %v", sec.Name, err)
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}
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return string(bytes.TrimRight(data, "\000")), nil
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}
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func loadVersion(sec *elf.Section, bo binary.ByteOrder) (uint32, error) {
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if sec == nil {
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return 0, nil
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}
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var version uint32
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if err := binary.Read(sec.Open(), bo, &version); err != nil {
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return 0, xerrors.Errorf("section %s: %v", sec.Name, err)
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}
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return version, nil
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}
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func (ec *elfCode) loadPrograms(progSections map[elf.SectionIndex]*elf.Section, relocations map[elf.SectionIndex]map[uint64]elf.Symbol, btf *btf.Spec) (map[string]*ProgramSpec, error) {
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var (
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progs []*ProgramSpec
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libs []*ProgramSpec
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)
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for idx, sec := range progSections {
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syms := ec.symbolsPerSection[idx]
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if len(syms) == 0 {
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return nil, xerrors.Errorf("section %v: missing symbols", sec.Name)
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}
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funcSym, ok := syms[0]
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if !ok {
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return nil, xerrors.Errorf("section %v: no label at start", sec.Name)
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}
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insns, length, err := ec.loadInstructions(sec, syms, relocations[idx])
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if err != nil {
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return nil, xerrors.Errorf("program %s: can't unmarshal instructions: %w", funcSym.Name, err)
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}
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progType, attachType, attachTo := getProgType(sec.Name)
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spec := &ProgramSpec{
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Name: funcSym.Name,
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Type: progType,
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AttachType: attachType,
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AttachTo: attachTo,
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License: ec.license,
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KernelVersion: ec.version,
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Instructions: insns,
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ByteOrder: ec.ByteOrder,
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}
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if btf != nil {
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spec.BTF, err = btf.Program(sec.Name, length)
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if err != nil {
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return nil, xerrors.Errorf("BTF for section %s (program %s): %w", sec.Name, funcSym.Name, err)
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}
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}
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if spec.Type == UnspecifiedProgram {
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// There is no single name we can use for "library" sections,
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// since they may contain multiple functions. We'll decode the
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// labels they contain later on, and then link sections that way.
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libs = append(libs, spec)
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} else {
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progs = append(progs, spec)
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}
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}
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res := make(map[string]*ProgramSpec, len(progs))
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for _, prog := range progs {
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err := link(prog, libs)
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if err != nil {
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return nil, xerrors.Errorf("program %s: %w", prog.Name, err)
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}
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res[prog.Name] = prog
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}
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return res, nil
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}
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func (ec *elfCode) loadInstructions(section *elf.Section, symbols, relocations map[uint64]elf.Symbol) (asm.Instructions, uint64, error) {
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var (
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r = section.Open()
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insns asm.Instructions
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offset uint64
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)
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for {
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var ins asm.Instruction
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n, err := ins.Unmarshal(r, ec.ByteOrder)
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if err == io.EOF {
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return insns, offset, nil
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}
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if err != nil {
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return nil, 0, xerrors.Errorf("offset %d: %w", offset, err)
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}
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ins.Symbol = symbols[offset].Name
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if rel, ok := relocations[offset]; ok {
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if err = ec.relocateInstruction(&ins, rel); err != nil {
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return nil, 0, xerrors.Errorf("offset %d: can't relocate instruction: %w", offset, err)
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}
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}
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insns = append(insns, ins)
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offset += n
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}
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}
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func (ec *elfCode) relocateInstruction(ins *asm.Instruction, rel elf.Symbol) error {
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var (
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typ = elf.ST_TYPE(rel.Info)
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bind = elf.ST_BIND(rel.Info)
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name = rel.Name
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)
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if typ == elf.STT_SECTION {
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// Symbols with section type do not have a name set. Get it
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// from the section itself.
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idx := int(rel.Section)
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if idx > len(ec.Sections) {
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return xerrors.New("out-of-bounds section index")
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}
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name = ec.Sections[idx].Name
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}
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outer:
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switch {
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case ins.OpCode == asm.LoadImmOp(asm.DWord):
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// There are two distinct types of a load from a map:
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// a direct one, where the value is extracted without
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// a call to map_lookup_elem in eBPF, and an indirect one
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// that goes via the helper. They are distinguished by
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// different relocations.
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switch typ {
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case elf.STT_SECTION:
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// This is a direct load since the referenced symbol is a
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// section. Weirdly, the offset of the real symbol in the
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// section is encoded in the instruction stream.
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if bind != elf.STB_LOCAL {
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return xerrors.Errorf("direct load: %s: unsupported relocation %s", name, bind)
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}
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// For some reason, clang encodes the offset of the symbol its
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// section in the first basic BPF instruction, while the kernel
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// expects it in the second one.
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ins.Constant <<= 32
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ins.Src = asm.PseudoMapValue
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case elf.STT_NOTYPE:
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if bind == elf.STB_GLOBAL && rel.Section == elf.SHN_UNDEF {
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// This is a relocation generated by inline assembly.
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// We can't do more than assigning ins.Reference.
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break outer
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}
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// This is an ELF generated on clang < 8, which doesn't tag
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// relocations appropriately.
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fallthrough
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case elf.STT_OBJECT:
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if bind != elf.STB_GLOBAL {
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return xerrors.Errorf("load: %s: unsupported binding: %s", name, bind)
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}
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ins.Src = asm.PseudoMapFD
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default:
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return xerrors.Errorf("load: %s: unsupported relocation: %s", name, typ)
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}
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// Mark the instruction as needing an update when creating the
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// collection.
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if err := ins.RewriteMapPtr(-1); err != nil {
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return err
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}
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case ins.OpCode.JumpOp() == asm.Call:
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if ins.Src != asm.PseudoCall {
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return xerrors.Errorf("call: %s: incorrect source register", name)
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}
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switch typ {
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case elf.STT_NOTYPE, elf.STT_FUNC:
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if bind != elf.STB_GLOBAL {
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return xerrors.Errorf("call: %s: unsupported binding: %s", name, bind)
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}
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case elf.STT_SECTION:
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if bind != elf.STB_LOCAL {
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return xerrors.Errorf("call: %s: unsupported binding: %s", name, bind)
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}
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// The function we want to call is in the indicated section,
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// at the offset encoded in the instruction itself. Reverse
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// the calculation to find the real function we're looking for.
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// A value of -1 references the first instruction in the section.
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offset := int64(int32(ins.Constant)+1) * asm.InstructionSize
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if offset < 0 {
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return xerrors.Errorf("call: %s: invalid offset %d", name, offset)
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}
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sym, ok := ec.symbolsPerSection[rel.Section][uint64(offset)]
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if !ok {
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return xerrors.Errorf("call: %s: no symbol at offset %d", name, offset)
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}
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ins.Constant = -1
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name = sym.Name
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default:
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return xerrors.Errorf("call: %s: invalid symbol type %s", name, typ)
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}
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default:
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return xerrors.Errorf("relocation for unsupported instruction: %s", ins.OpCode)
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}
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ins.Reference = name
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return nil
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}
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func (ec *elfCode) loadMaps(maps map[string]*MapSpec, mapSections map[elf.SectionIndex]*elf.Section) error {
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for idx, sec := range mapSections {
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syms := ec.symbolsPerSection[idx]
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if len(syms) == 0 {
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return xerrors.Errorf("section %v: no symbols", sec.Name)
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}
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if sec.Size%uint64(len(syms)) != 0 {
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return xerrors.Errorf("section %v: map descriptors are not of equal size", sec.Name)
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}
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var (
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r = sec.Open()
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size = sec.Size / uint64(len(syms))
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)
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for i, offset := 0, uint64(0); i < len(syms); i, offset = i+1, offset+size {
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mapSym, ok := syms[offset]
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if !ok {
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return xerrors.Errorf("section %s: missing symbol for map at offset %d", sec.Name, offset)
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}
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if maps[mapSym.Name] != nil {
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return xerrors.Errorf("section %v: map %v already exists", sec.Name, mapSym)
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}
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lr := io.LimitReader(r, int64(size))
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spec := MapSpec{
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Name: SanitizeName(mapSym.Name, -1),
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}
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switch {
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case binary.Read(lr, ec.ByteOrder, &spec.Type) != nil:
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return xerrors.Errorf("map %v: missing type", mapSym)
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case binary.Read(lr, ec.ByteOrder, &spec.KeySize) != nil:
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return xerrors.Errorf("map %v: missing key size", mapSym)
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case binary.Read(lr, ec.ByteOrder, &spec.ValueSize) != nil:
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return xerrors.Errorf("map %v: missing value size", mapSym)
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case binary.Read(lr, ec.ByteOrder, &spec.MaxEntries) != nil:
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return xerrors.Errorf("map %v: missing max entries", mapSym)
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case binary.Read(lr, ec.ByteOrder, &spec.Flags) != nil:
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return xerrors.Errorf("map %v: missing flags", mapSym)
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}
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if _, err := io.Copy(internal.DiscardZeroes{}, lr); err != nil {
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return xerrors.Errorf("map %v: unknown and non-zero fields in definition", mapSym)
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}
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maps[mapSym.Name] = &spec
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}
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}
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return nil
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}
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func (ec *elfCode) loadBTFMaps(maps map[string]*MapSpec, mapSections map[elf.SectionIndex]*elf.Section, spec *btf.Spec) error {
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if spec == nil {
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return xerrors.Errorf("missing BTF")
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}
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for idx, sec := range mapSections {
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syms := ec.symbolsPerSection[idx]
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if len(syms) == 0 {
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return xerrors.Errorf("section %v: no symbols", sec.Name)
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}
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for _, sym := range syms {
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name := sym.Name
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if maps[name] != nil {
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return xerrors.Errorf("section %v: map %v already exists", sec.Name, sym)
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}
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btfMap, btfMapMembers, err := spec.Map(name)
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if err != nil {
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return xerrors.Errorf("map %v: can't get BTF: %w", name, err)
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}
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spec, err := mapSpecFromBTF(btfMap, btfMapMembers)
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if err != nil {
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return xerrors.Errorf("map %v: %w", name, err)
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}
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maps[name] = spec
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}
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}
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return nil
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}
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func mapSpecFromBTF(btfMap *btf.Map, btfMapMembers []btf.Member) (*MapSpec, error) {
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var (
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mapType, flags, maxEntries uint32
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err error
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)
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for _, member := range btfMapMembers {
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switch member.Name {
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case "type":
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mapType, err = uintFromBTF(member.Type)
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if err != nil {
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return nil, xerrors.Errorf("can't get type: %w", err)
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}
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case "map_flags":
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flags, err = uintFromBTF(member.Type)
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if err != nil {
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return nil, xerrors.Errorf("can't get BTF map flags: %w", err)
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}
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case "max_entries":
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maxEntries, err = uintFromBTF(member.Type)
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if err != nil {
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return nil, xerrors.Errorf("can't get BTF map max entries: %w", err)
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}
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case "key":
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case "value":
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default:
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return nil, xerrors.Errorf("unrecognized field %s in BTF map definition", member.Name)
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}
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}
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keySize, err := btf.Sizeof(btf.MapKey(btfMap))
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if err != nil {
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return nil, xerrors.Errorf("can't get size of BTF key: %w", err)
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}
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valueSize, err := btf.Sizeof(btf.MapValue(btfMap))
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if err != nil {
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return nil, xerrors.Errorf("can't get size of BTF value: %w", err)
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}
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return &MapSpec{
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Type: MapType(mapType),
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KeySize: uint32(keySize),
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ValueSize: uint32(valueSize),
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MaxEntries: maxEntries,
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Flags: flags,
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BTF: btfMap,
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}, nil
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}
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// uintFromBTF resolves the __uint macro, which is a pointer to a sized
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// array, e.g. for int (*foo)[10], this function will return 10.
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func uintFromBTF(typ btf.Type) (uint32, error) {
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ptr, ok := typ.(*btf.Pointer)
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if !ok {
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return 0, xerrors.Errorf("not a pointer: %v", typ)
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}
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arr, ok := ptr.Target.(*btf.Array)
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if !ok {
|
|
return 0, xerrors.Errorf("not a pointer to array: %v", typ)
|
|
}
|
|
|
|
return arr.Nelems, nil
|
|
}
|
|
|
|
func (ec *elfCode) loadDataSections(maps map[string]*MapSpec, dataSections map[elf.SectionIndex]*elf.Section, spec *btf.Spec) error {
|
|
if spec == nil {
|
|
return xerrors.New("data sections require BTF, make sure all consts are marked as static")
|
|
}
|
|
|
|
for _, sec := range dataSections {
|
|
btfMap, err := spec.Datasec(sec.Name)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
|
|
data, err := sec.Data()
|
|
if err != nil {
|
|
return xerrors.Errorf("data section %s: can't get contents: %w", sec.Name, err)
|
|
}
|
|
|
|
if uint64(len(data)) > math.MaxUint32 {
|
|
return xerrors.Errorf("data section %s: contents exceed maximum size", sec.Name)
|
|
}
|
|
|
|
mapSpec := &MapSpec{
|
|
Name: SanitizeName(sec.Name, -1),
|
|
Type: Array,
|
|
KeySize: 4,
|
|
ValueSize: uint32(len(data)),
|
|
MaxEntries: 1,
|
|
Contents: []MapKV{{uint32(0), data}},
|
|
BTF: btfMap,
|
|
}
|
|
|
|
switch sec.Name {
|
|
case ".rodata":
|
|
mapSpec.Flags = unix.BPF_F_RDONLY_PROG
|
|
mapSpec.Freeze = true
|
|
case ".bss":
|
|
// The kernel already zero-initializes the map
|
|
mapSpec.Contents = nil
|
|
}
|
|
|
|
maps[sec.Name] = mapSpec
|
|
}
|
|
return nil
|
|
}
|
|
|
|
func getProgType(sectionName string) (ProgramType, AttachType, string) {
|
|
types := map[string]struct {
|
|
progType ProgramType
|
|
attachType AttachType
|
|
}{
|
|
// From https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/bpf/libbpf.c
|
|
"socket": {SocketFilter, AttachNone},
|
|
"seccomp": {SocketFilter, AttachNone},
|
|
"kprobe/": {Kprobe, AttachNone},
|
|
"uprobe/": {Kprobe, AttachNone},
|
|
"kretprobe/": {Kprobe, AttachNone},
|
|
"uretprobe/": {Kprobe, AttachNone},
|
|
"tracepoint/": {TracePoint, AttachNone},
|
|
"raw_tracepoint/": {RawTracepoint, AttachNone},
|
|
"xdp": {XDP, AttachNone},
|
|
"perf_event": {PerfEvent, AttachNone},
|
|
"lwt_in": {LWTIn, AttachNone},
|
|
"lwt_out": {LWTOut, AttachNone},
|
|
"lwt_xmit": {LWTXmit, AttachNone},
|
|
"lwt_seg6local": {LWTSeg6Local, AttachNone},
|
|
"sockops": {SockOps, AttachCGroupSockOps},
|
|
"sk_skb/stream_parser": {SkSKB, AttachSkSKBStreamParser},
|
|
"sk_skb/stream_verdict": {SkSKB, AttachSkSKBStreamParser},
|
|
"sk_msg": {SkMsg, AttachSkSKBStreamVerdict},
|
|
"lirc_mode2": {LircMode2, AttachLircMode2},
|
|
"flow_dissector": {FlowDissector, AttachFlowDissector},
|
|
"iter/": {Tracing, AttachTraceIter},
|
|
|
|
"cgroup_skb/ingress": {CGroupSKB, AttachCGroupInetIngress},
|
|
"cgroup_skb/egress": {CGroupSKB, AttachCGroupInetEgress},
|
|
"cgroup/dev": {CGroupDevice, AttachCGroupDevice},
|
|
"cgroup/skb": {CGroupSKB, AttachNone},
|
|
"cgroup/sock": {CGroupSock, AttachCGroupInetSockCreate},
|
|
"cgroup/post_bind4": {CGroupSock, AttachCGroupInet4PostBind},
|
|
"cgroup/post_bind6": {CGroupSock, AttachCGroupInet6PostBind},
|
|
"cgroup/bind4": {CGroupSockAddr, AttachCGroupInet4Bind},
|
|
"cgroup/bind6": {CGroupSockAddr, AttachCGroupInet6Bind},
|
|
"cgroup/connect4": {CGroupSockAddr, AttachCGroupInet4Connect},
|
|
"cgroup/connect6": {CGroupSockAddr, AttachCGroupInet6Connect},
|
|
"cgroup/sendmsg4": {CGroupSockAddr, AttachCGroupUDP4Sendmsg},
|
|
"cgroup/sendmsg6": {CGroupSockAddr, AttachCGroupUDP6Sendmsg},
|
|
"cgroup/recvmsg4": {CGroupSockAddr, AttachCGroupUDP4Recvmsg},
|
|
"cgroup/recvmsg6": {CGroupSockAddr, AttachCGroupUDP6Recvmsg},
|
|
"cgroup/sysctl": {CGroupSysctl, AttachCGroupSysctl},
|
|
"cgroup/getsockopt": {CGroupSockopt, AttachCGroupGetsockopt},
|
|
"cgroup/setsockopt": {CGroupSockopt, AttachCGroupSetsockopt},
|
|
"classifier": {SchedCLS, AttachNone},
|
|
"action": {SchedACT, AttachNone},
|
|
}
|
|
|
|
for prefix, t := range types {
|
|
if !strings.HasPrefix(sectionName, prefix) {
|
|
continue
|
|
}
|
|
|
|
if !strings.HasSuffix(prefix, "/") {
|
|
return t.progType, t.attachType, ""
|
|
}
|
|
|
|
return t.progType, t.attachType, sectionName[len(prefix):]
|
|
}
|
|
|
|
return UnspecifiedProgram, AttachNone, ""
|
|
}
|
|
|
|
func (ec *elfCode) loadRelocations(sections map[elf.SectionIndex]*elf.Section) (map[elf.SectionIndex]map[uint64]elf.Symbol, error) {
|
|
result := make(map[elf.SectionIndex]map[uint64]elf.Symbol)
|
|
for idx, sec := range sections {
|
|
rels := make(map[uint64]elf.Symbol)
|
|
|
|
if sec.Entsize < 16 {
|
|
return nil, xerrors.Errorf("section %s: relocations are less than 16 bytes", sec.Name)
|
|
}
|
|
|
|
r := sec.Open()
|
|
for off := uint64(0); off < sec.Size; off += sec.Entsize {
|
|
ent := io.LimitReader(r, int64(sec.Entsize))
|
|
|
|
var rel elf.Rel64
|
|
if binary.Read(ent, ec.ByteOrder, &rel) != nil {
|
|
return nil, xerrors.Errorf("can't parse relocation at offset %v", off)
|
|
}
|
|
|
|
symNo := int(elf.R_SYM64(rel.Info) - 1)
|
|
if symNo >= len(ec.symbols) {
|
|
return nil, xerrors.Errorf("relocation at offset %d: symbol %v doesnt exist", off, symNo)
|
|
}
|
|
|
|
rels[rel.Off] = ec.symbols[symNo]
|
|
}
|
|
|
|
result[idx] = rels
|
|
}
|
|
return result, nil
|
|
}
|
|
|
|
func symbolsPerSection(symbols []elf.Symbol) map[elf.SectionIndex]map[uint64]elf.Symbol {
|
|
result := make(map[elf.SectionIndex]map[uint64]elf.Symbol)
|
|
for _, sym := range symbols {
|
|
switch elf.ST_TYPE(sym.Info) {
|
|
case elf.STT_NOTYPE:
|
|
// Older versions of LLVM doesn't tag
|
|
// symbols correctly.
|
|
break
|
|
case elf.STT_OBJECT:
|
|
break
|
|
case elf.STT_FUNC:
|
|
break
|
|
default:
|
|
continue
|
|
}
|
|
|
|
if sym.Section == elf.SHN_UNDEF || sym.Section >= elf.SHN_LORESERVE {
|
|
continue
|
|
}
|
|
|
|
if sym.Name == "" {
|
|
continue
|
|
}
|
|
|
|
idx := sym.Section
|
|
if _, ok := result[idx]; !ok {
|
|
result[idx] = make(map[uint64]elf.Symbol)
|
|
}
|
|
result[idx][sym.Value] = sym
|
|
}
|
|
return result
|
|
}
|