Method loadBTFMaps

elf_reader.go:904–978

loadBTFMaps iterates over all ELF sections marked as BTF map sections (like .maps) and parses them into MapSpecs. Dump the .maps section and any relocations with `readelf -x .maps -r `.

()

// (like .maps) and parses them into MapSpecs. Dump the .maps section and
// any relocations with `readelf -x .maps -r <elf_file>`.
func (ec *elfCode) loadBTFMaps() error {
	for _, sec := range ec.sections {
		if sec.kind != btfMapSection {
			continue
		}

		if ec.btf == nil {
			return fmt.Errorf("missing BTF")
		}

		if sec.ReaderAt == nil {
			return fmt.Errorf("compressed BTF map section is not supported")
		}

		vars, err := ec.sectionVars(ec.btf, sec.Name)
		if err != nil {
			return fmt.Errorf("section %v: loading map variable BTF: %w", sec.Name, err)
		}

		if len(vars) != len(sec.symbols) {
			return fmt.Errorf("section %v: contains %d symbols but %d btf.Vars", sec.Name, len(sec.symbols), len(vars))
		}

		syms := make(map[string]elf.Symbol)
		for _, sym := range sec.symbols {
			syms[sym.Name] = sym
		}

		for _, v := range vars {
			name := v.Name

			// Find the ELF symbol corresponding to this Var.
			sym, ok := syms[name]
			if !ok {
				return fmt.Errorf("section %v: missing symbol for map %s", sec.Name, name)
			}

			if sym.Value > math.MaxUint32 || sym.Size > math.MaxUint32 {
				return fmt.Errorf("symbol %s: offset or size exceeds 32 bits in section %s", sym.Name, sec.Name)
			}
			if sym.Value+sym.Size > sec.Size {
				return fmt.Errorf("section %v: symbol %s: size goes out of bounds of section", sec.Name, name)
			}

			sr := internal.NewBufferedSectionReader(sec, int64(sym.Value), int64(sym.Size))

			// The BTF metadata for each Var contains the full length of the map
			// declaration, so read the corresponding amount of bytes from the ELF.
			// This way, we can pinpoint which map declaration contains unexpected
			// (and therefore unsupported) data.
			if _, err = io.Copy(internal.DiscardZeroes{}, sr); err != nil {
				return fmt.Errorf("section %v: map %s: initializing BTF map definitions: %w", sec.Name, name, internal.ErrNotSupported)
			}

			if ec.maps[name] != nil {
				return fmt.Errorf("section %v: map %s already exists", sec.Name, name)
			}