func doAppleOS()

in util/fipstools/inject_hash/inject_hash.go [171:309]
108 lines of code
41 McCabe index (conditional complexity)

func doAppleOS(objectBytes []byte) ([]byte, []byte, error) {

	object, err := macho.NewFile(bytes.NewReader(objectBytes))
	if err != nil {
		return nil, nil, errors.New("failed to parse object: " + err.Error())
	}

	// Find the __text and, optionally, __const sections.
	// They are both in __TEXT segment and are unique.
	var textSection, rodataSection *macho.Section
	var textSectionIndex, rodataSectionIndex int
	for i, section := range object.Sections {
		if section.Seg == "__TEXT" && section.Name == "__text" {
			textSection = section
			textSectionIndex = i + 1
		}
		if section.Seg == "__TEXT" && section.Name == "__const" {
			rodataSection = section
			rodataSectionIndex = i + 1
		}
	}

	if textSection == nil {
		return nil, nil, errors.New("failed to find __text section in object")
	}

	// Find the starting and ending symbols for the module.
	var textStart, textEnd, rodataStart, rodataEnd *uint64

	symbols := object.Symtab.Syms
	if symbols == nil {
		return nil, nil, errors.New("failed to parse symbols: " + err.Error())
	}

	for _, symbol := range symbols {
		var base uint64
		switch int(symbol.Sect) {
		case textSectionIndex:
			base = textSection.Addr
		case rodataSectionIndex:
			if rodataSection == nil {
				continue
			}
			base = rodataSection.Addr
		default:
			continue
		}

		if symbol.Name != "" && symbol.Name != " " && symbol.Value < base {
			return nil, nil, fmt.Errorf("symbol %q at %x, which is below base of %x\n", symbol.Name, symbol.Value, base)
		}

		// Skip debugging symbols
		//
		// #define	N_STAB	0xe0  /* if any of these bits set, a symbolic debugging entry */
		//
		// "Only symbolic debugging entries have some of the N_STAB bits set and if any of these bits are set then it is
		// a symbolic debugging entry (a stab).  In which case then the values of the n_type field (the entire field)
		// are given in <mach-o/stab.h>"
		//
		// https://github.com/apple-oss-distributions/xnu/blob/main/EXTERNAL_HEADERS/mach-o/nlist.h
		if symbol.Type&0xe0 != 0 {
			continue
		}

		value := symbol.Value - base
		switch symbol.Name {
		case "_BORINGSSL_bcm_text_start":
			if textStart != nil {
				return nil, nil, errors.New("duplicate start symbol found")
			}
			textStart = &value
		case "_BORINGSSL_bcm_text_end":
			if textEnd != nil {
				return nil, nil, errors.New("duplicate end symbol found")
			}
			textEnd = &value
		case "_BORINGSSL_bcm_rodata_start":
			if rodataStart != nil {
				return nil, nil, errors.New("duplicate rodata start symbol found")
			}
			rodataStart = &value
		case "_BORINGSSL_bcm_rodata_end":
			if rodataEnd != nil {
				return nil, nil, errors.New("duplicate rodata end symbol found")
			}
			rodataEnd = &value
		default:
			continue
		}
	}

	if textStart == nil || textEnd == nil {
		return nil, nil, errors.New("could not find .text module boundaries in object")
	}

	if (rodataStart == nil) != (rodataSection == nil) {
		return nil, nil, errors.New("rodata start marker inconsistent with rodata section presence")
	}

	if (rodataStart != nil) != (rodataEnd != nil) {
		return nil, nil, errors.New("rodata marker presence inconsistent")
	}

	if max := textSection.Size; *textStart > max || *textStart > *textEnd || *textEnd > max {
		return nil, nil, fmt.Errorf("invalid module __text boundaries: start: %x, end: %x, max: %x", *textStart, *textEnd, max)
	}

	if rodataSection != nil {
		if max := rodataSection.Size; *rodataStart > max || *rodataStart > *rodataEnd || *rodataEnd > max {
			return nil, nil, fmt.Errorf("invalid module __const boundaries: start: %x, end: %x, max: %x", *rodataStart, *rodataEnd, max)
		}
	}

	// Extract the module from the __text section.
	text := textSection.Open()
	if _, err := text.Seek(int64(*textStart), 0); err != nil {
		return nil, nil, errors.New("failed to seek to module start in __text: " + err.Error())
	}
	moduleText := make([]byte, *textEnd-*textStart)
	if _, err := io.ReadFull(text, moduleText); err != nil {
		return nil, nil, errors.New("failed to read __text: " + err.Error())
	}

	// Maybe extract the module's read-only data too
	var moduleROData []byte
	if rodataSection != nil {
		rodata := rodataSection.Open()
		if _, err := rodata.Seek(int64(*rodataStart), 0); err != nil {
			return nil, nil, errors.New("failed to seek to module start in __const: " + err.Error())
		}
		moduleROData = make([]byte, *rodataEnd-*rodataStart)
		if _, err := io.ReadFull(rodata, moduleROData); err != nil {
			return nil, nil, errors.New("failed to read __const: " + err.Error())
		}
	}

	return moduleText, moduleROData, nil
}