Function LoadCollectionSpecFromReader

elf_reader.go:78–212

LoadCollectionSpecFromReader parses an ELF file into a CollectionSpec.

(rd io.ReaderAt)

// LoadCollectionSpecFromReader parses an ELF file into a CollectionSpec.
func LoadCollectionSpecFromReader(rd io.ReaderAt) (*CollectionSpec, error) {
	f, err := internal.NewSafeELFFile(rd)
	if err != nil {
		return nil, err
	}

	// Checks if the ELF file is for BPF data.
	// Old LLVM versions set e_machine to EM_NONE.
	if f.Machine != elf.EM_NONE && f.Machine != elf.EM_BPF {
		return nil, fmt.Errorf("unexpected machine type for BPF ELF: %s", f.Machine)
	}

	var (
		licenseSection *elf.Section
		versionSection *elf.Section
		sections       = make(map[elf.SectionIndex]*elfSection)
		relSections    = make(map[elf.SectionIndex]*elf.Section)
	)

	// This is the target of relocations generated by inline assembly.
	sections[elf.SHN_UNDEF] = newElfSection(new(elf.Section), undefSection)

	// Collect all the sections we're interested in. This includes relocations
	// which we parse later.
	//
	// Keep the documentation at docs/ebpf/loading/elf-sections.md up-to-date.
	for i, sec := range f.Sections {
		idx := elf.SectionIndex(i)

		switch {
		case strings.HasPrefix(sec.Name, "license"):
			licenseSection = sec
		case strings.HasPrefix(sec.Name, "version"):
			versionSection = sec
		case strings.HasPrefix(sec.Name, "maps"):
			sections[idx] = newElfSection(sec, mapSection)
		case sec.Name == ".maps":
			sections[idx] = newElfSection(sec, btfMapSection)
		case isDataSection(sec.Name):
			sections[idx] = newElfSection(sec, dataSection)
		case sec.Type == elf.SHT_REL:
			// Store relocations under the section index of the target
			relSections[elf.SectionIndex(sec.Info)] = sec
		case sec.Type == elf.SHT_PROGBITS && sec.Size > 0:
			if (sec.Flags&elf.SHF_EXECINSTR) != 0 && sec.Size > 0 {
				sections[idx] = newElfSection(sec, programSection)
			} else if sec.Name == structOpsLinkSec {
				// classification based on sec names so that struct_ops-specific
				// sections (.struct_ops.link) is correctly recognized
				// as non-executable PROGBITS, allowing value placement and link metadata to be loaded.
				sections[idx] = newElfSection(sec, structOpsSection)
			} else if sec.Name == structOpsSec {
				return nil, fmt.Errorf("section %q: got '.struct_ops' section: %w", sec.Name, ErrNotSupported)
			}
		}
	}

	license, err := loadLicense(licenseSection)