src/cmd/vendor/github.com/google/pprof/internal/elfexec/elfexec.go - toolchain/go - Git at Google

 // Copyright 2014 Google Inc. All Rights Reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 // Package elfexec provides utility routines to examine ELF binaries.
 package elfexec

 import (
 	"bufio"
 	"debug/elf"
 	"encoding/binary"
 	"fmt"
 	"io"
 )

 const (
 	maxNoteSize        = 1 << 20 // in bytes
 	noteTypeGNUBuildID = 3
 )

 // elfNote is the payload of a Note Section in an ELF file.
 type elfNote struct {
 	Name string // Contents of the "name" field, omitting the trailing zero byte.
 	Desc []byte // Contents of the "desc" field.
 	Type uint32 // Contents of the "type" field.
 }

 // parseNotes returns the notes from a SHT_NOTE section or PT_NOTE segment.
 func parseNotes(reader io.Reader, alignment int, order binary.ByteOrder) ([]elfNote, error) {
 	r := bufio.NewReader(reader)

 	// padding returns the number of bytes required to pad the given size to an
 	// alignment boundary.
 	padding := func(size int) int {
 		return ((size + (alignment - 1)) &^ (alignment - 1)) - size
 	}

 	var notes []elfNote
 	for {
 		noteHeader := make([]byte, 12) // 3 4-byte words
 		if _, err := io.ReadFull(r, noteHeader); err == io.EOF {
 			break
 		} else if err != nil {
 			return nil, err
 		}
 		namesz := order.Uint32(noteHeader[0:4])
 		descsz := order.Uint32(noteHeader[4:8])
 		typ := order.Uint32(noteHeader[8:12])

 		if uint64(namesz) > uint64(maxNoteSize) {
 			return nil, fmt.Errorf("note name too long (%d bytes)", namesz)
 		}
 		var name string
 		if namesz > 0 {
 			// Documentation differs as to whether namesz is meant to include the
 			// trailing zero, but everyone agrees that name is null-terminated.
 			// So we'll just determine the actual length after the fact.
 			var err error
 			name, err = r.ReadString('\x00')
 			if err == io.EOF {
 				return nil, fmt.Errorf("missing note name (want %d bytes)", namesz)
 			} else if err != nil {
 				return nil, err
 			}
 			namesz = uint32(len(name))
 			name = name[:len(name)-1]
 		}

 		// Drop padding bytes until the desc field.
 		for n := padding(len(noteHeader) + int(namesz)); n > 0; n-- {
 			if _, err := r.ReadByte(); err == io.EOF {
 				return nil, fmt.Errorf(
 					"missing %d bytes of padding after note name", n)
 			} else if err != nil {
 				return nil, err
 			}
 		}

 		if uint64(descsz) > uint64(maxNoteSize) {
 			return nil, fmt.Errorf("note desc too long (%d bytes)", descsz)
 		}
 		desc := make([]byte, int(descsz))
 		if _, err := io.ReadFull(r, desc); err == io.EOF {
 			return nil, fmt.Errorf("missing desc (want %d bytes)", len(desc))
 		} else if err != nil {
 			return nil, err
 		}

 		notes = append(notes, elfNote{Name: name, Desc: desc, Type: typ})

 		// Drop padding bytes until the next note or the end of the section,
 		// whichever comes first.
 		for n := padding(len(desc)); n > 0; n-- {
 			if _, err := r.ReadByte(); err == io.EOF {
 				// We hit the end of the section before an alignment boundary.
 				// This can happen if this section is at the end of the file or the next
 				// section has a smaller alignment requirement.
 				break
 			} else if err != nil {
 				return nil, err
 			}
 		}
 	}
 	return notes, nil
 }

 // GetBuildID returns the GNU build-ID for an ELF binary.
 //
 // If no build-ID was found but the binary was read without error, it returns
 // (nil, nil).
 func GetBuildID(binary io.ReaderAt) ([]byte, error) {
 	f, err := elf.NewFile(binary)
 	if err != nil {
 		return nil, err
 	}

 	findBuildID := func(notes []elfNote) ([]byte, error) {
 		var buildID []byte
 		for _, note := range notes {
 			if note.Name == "GNU" && note.Type == noteTypeGNUBuildID {
 				if buildID == nil {
 					buildID = note.Desc
 				} else {
 					return nil, fmt.Errorf("multiple build ids found, don't know which to use")
 				}
 			}
 		}
 		return buildID, nil
 	}

 	for _, p := range f.Progs {
 		if p.Type != elf.PT_NOTE {
 			continue
 		}
 		notes, err := parseNotes(p.Open(), int(p.Align), f.ByteOrder)
 		if err != nil {
 			return nil, err
 		}
 		if b, err := findBuildID(notes); b != nil || err != nil {
 			return b, err
 		}
 	}
 	for _, s := range f.Sections {
 		if s.Type != elf.SHT_NOTE {
 			continue
 		}
 		notes, err := parseNotes(s.Open(), int(s.Addralign), f.ByteOrder)
 		if err != nil {
 			return nil, err
 		}
 		if b, err := findBuildID(notes); b != nil || err != nil {
 			return b, err
 		}
 	}
 	return nil, nil
 }

 // GetBase determines the base address to subtract from virtual
 // address to get symbol table address. For an executable, the base
 // is 0. Otherwise, it's a shared library, and the base is the
 // address where the mapping starts. The kernel is special, and may
 // use the address of the _stext symbol as the mmap start. _stext
 // offset can be obtained with `nm vmlinux | grep _stext`
 func GetBase(fh *elf.FileHeader, loadSegment *elf.ProgHeader, stextOffset *uint64, start, limit, offset uint64) (uint64, error) {
 	const (
 		pageSize = 4096
 		// PAGE_OFFSET for PowerPC64, see arch/powerpc/Kconfig in the kernel sources.
 		pageOffsetPpc64 = 0xc000000000000000
 	)

 	if start == 0 && offset == 0 &&
 		(limit == ^uint64(0) || limit == 0) {
 		// Some tools may introduce a fake mapping that spans the entire
 		// address space. Assume that the address has already been
 		// adjusted, so no additional base adjustment is necessary.
 		return 0, nil
 	}

 	switch fh.Type {
 	case elf.ET_EXEC:
 		if loadSegment == nil {
 			// Fixed-address executable, no adjustment.
 			return 0, nil
 		}
 		if start == 0 && limit != 0 {
 			// ChromeOS remaps its kernel to 0. Nothing else should come
 			// down this path. Empirical values:
 			//       VADDR=0xffffffff80200000
 			// stextOffset=0xffffffff80200198
 			if stextOffset != nil {
 				return -*stextOffset, nil
 			}
 			return -loadSegment.Vaddr, nil
 		}
 		if loadSegment.Vaddr-loadSegment.Off == start-offset {
 			return offset, nil
 		}
 		if loadSegment.Vaddr == start-offset {
 			return offset, nil
 		}
 		if start >= loadSegment.Vaddr && limit > start && (offset == 0 || offset == pageOffsetPpc64) {
 			// Some kernels look like:
 			//       VADDR=0xffffffff80200000
 			// stextOffset=0xffffffff80200198
 			//       Start=0xffffffff83200000
 			//       Limit=0xffffffff84200000
 			//      Offset=0 (0xc000000000000000 for PowerPC64)
 			// So the base should be:
 			if stextOffset != nil && (start%pageSize) == (*stextOffset%pageSize) {
 				// perf uses the address of _stext as start. Some tools may
 				// adjust for this before calling GetBase, in which case the the page
 				// alignment should be different from that of stextOffset.
 				return start - *stextOffset, nil
 			}

 			return start - loadSegment.Vaddr, nil
 		} else if start%pageSize != 0 && stextOffset != nil && *stextOffset%pageSize == start%pageSize {
 			// ChromeOS remaps its kernel to 0 + start%pageSize. Nothing
 			// else should come down this path. Empirical values:
 			//       start=0x198 limit=0x2f9fffff offset=0
 			//       VADDR=0xffffffff81000000
 			// stextOffset=0xffffffff81000198
 			return -(*stextOffset - start), nil
 		}

 		return 0, fmt.Errorf("Don't know how to handle EXEC segment: %v start=0x%x limit=0x%x offset=0x%x", *loadSegment, start, limit, offset)
 	case elf.ET_REL:
 		if offset != 0 {
 			return 0, fmt.Errorf("Don't know how to handle mapping.Offset")
 		}
 		return start, nil
 	case elf.ET_DYN:
 		// The process mapping information, start = start of virtual address range,
 		// and offset = offset in the executable file of the start address, tells us
 		// that a runtime virtual address x maps to a file offset
 		// fx = x - start + offset.
 		if loadSegment == nil {
 			return start - offset, nil
 		}
 		// The program header, if not nil, indicates the offset in the file where
 		// the executable segment is located (loadSegment.Off), and the base virtual
 		// address where the first byte of the segment is loaded
 		// (loadSegment.Vaddr). A file offset fx maps to a virtual (symbol) address
 		// sx = fx - loadSegment.Off + loadSegment.Vaddr.
 		//
 		// Thus, a runtime virtual address x maps to a symbol address
 		// sx = x - start + offset - loadSegment.Off + loadSegment.Vaddr.
 		return start - offset + loadSegment.Off - loadSegment.Vaddr, nil
 	}
 	return 0, fmt.Errorf("Don't know how to handle FileHeader.Type %v", fh.Type)
 }
	// Copyright 2014 Google Inc. All Rights Reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	// Package elfexec provides utility routines to examine ELF binaries.
	package elfexec

	import (
	"bufio"
	"debug/elf"
	"encoding/binary"
	"fmt"
	"io"
	)

	const (
	maxNoteSize = 1 << 20 // in bytes
	noteTypeGNUBuildID = 3
	)

	// elfNote is the payload of a Note Section in an ELF file.
	type elfNote struct {
	Name string // Contents of the "name" field, omitting the trailing zero byte.
	Desc []byte // Contents of the "desc" field.
	Type uint32 // Contents of the "type" field.
	}

	// parseNotes returns the notes from a SHT_NOTE section or PT_NOTE segment.
	func parseNotes(reader io.Reader, alignment int, order binary.ByteOrder) ([]elfNote, error) {
	r := bufio.NewReader(reader)

	// padding returns the number of bytes required to pad the given size to an
	// alignment boundary.
	padding := func(size int) int {
	return ((size + (alignment - 1)) &^ (alignment - 1)) - size
	}

	var notes []elfNote
	for {
	noteHeader := make([]byte, 12) // 3 4-byte words
	if _, err := io.ReadFull(r, noteHeader); err == io.EOF {
	break
	} else if err != nil {
	return nil, err
	}
	namesz := order.Uint32(noteHeader[0:4])
	descsz := order.Uint32(noteHeader[4:8])
	typ := order.Uint32(noteHeader[8:12])

	if uint64(namesz) > uint64(maxNoteSize) {
	return nil, fmt.Errorf("note name too long (%d bytes)", namesz)
	}
	var name string
	if namesz > 0 {
	// Documentation differs as to whether namesz is meant to include the
	// trailing zero, but everyone agrees that name is null-terminated.
	// So we'll just determine the actual length after the fact.
	var err error
	name, err = r.ReadString('\x00')
	if err == io.EOF {
	return nil, fmt.Errorf("missing note name (want %d bytes)", namesz)
	} else if err != nil {
	return nil, err
	}
	namesz = uint32(len(name))
	name = name[:len(name)-1]
	}

	// Drop padding bytes until the desc field.
	for n := padding(len(noteHeader) + int(namesz)); n > 0; n-- {
	if _, err := r.ReadByte(); err == io.EOF {
	return nil, fmt.Errorf(
	"missing %d bytes of padding after note name", n)
	} else if err != nil {
	return nil, err
	}
	}

	if uint64(descsz) > uint64(maxNoteSize) {
	return nil, fmt.Errorf("note desc too long (%d bytes)", descsz)
	}
	desc := make([]byte, int(descsz))
	if _, err := io.ReadFull(r, desc); err == io.EOF {
	return nil, fmt.Errorf("missing desc (want %d bytes)", len(desc))
	} else if err != nil {
	return nil, err
	}

	notes = append(notes, elfNote{Name: name, Desc: desc, Type: typ})

	// Drop padding bytes until the next note or the end of the section,
	// whichever comes first.
	for n := padding(len(desc)); n > 0; n-- {
	if _, err := r.ReadByte(); err == io.EOF {
	// We hit the end of the section before an alignment boundary.
	// This can happen if this section is at the end of the file or the next
	// section has a smaller alignment requirement.
	break
	} else if err != nil {
	return nil, err
	}
	}
	}
	return notes, nil
	}

	// GetBuildID returns the GNU build-ID for an ELF binary.
	//
	// If no build-ID was found but the binary was read without error, it returns
	// (nil, nil).
	func GetBuildID(binary io.ReaderAt) ([]byte, error) {
	f, err := elf.NewFile(binary)
	if err != nil {
	return nil, err
	}

	findBuildID := func(notes []elfNote) ([]byte, error) {
	var buildID []byte
	for _, note := range notes {
	if note.Name == "GNU" && note.Type == noteTypeGNUBuildID {
	if buildID == nil {
	buildID = note.Desc
	} else {
	return nil, fmt.Errorf("multiple build ids found, don't know which to use")
	}
	}
	}
	return buildID, nil
	}

	for _, p := range f.Progs {
	if p.Type != elf.PT_NOTE {
	continue
	}
	notes, err := parseNotes(p.Open(), int(p.Align), f.ByteOrder)
	if err != nil {
	return nil, err
	}
	if b, err := findBuildID(notes); b != nil \|\| err != nil {
	return b, err
	}
	}
	for _, s := range f.Sections {
	if s.Type != elf.SHT_NOTE {
	continue
	}
	notes, err := parseNotes(s.Open(), int(s.Addralign), f.ByteOrder)
	if err != nil {
	return nil, err
	}
	if b, err := findBuildID(notes); b != nil \|\| err != nil {
	return b, err
	}
	}
	return nil, nil
	}

	// GetBase determines the base address to subtract from virtual
	// address to get symbol table address. For an executable, the base
	// is 0. Otherwise, it's a shared library, and the base is the
	// address where the mapping starts. The kernel is special, and may
	// use the address of the _stext symbol as the mmap start. _stext
	// offset can be obtained with `nm vmlinux \| grep _stext`
	func GetBase(fh elf.FileHeader, loadSegment elf.ProgHeader, stextOffset *uint64, start, limit, offset uint64) (uint64, error) {
	const (
	pageSize = 4096
	// PAGE_OFFSET for PowerPC64, see arch/powerpc/Kconfig in the kernel sources.
	pageOffsetPpc64 = 0xc000000000000000
	)

	if start == 0 && offset == 0 &&
	(limit == ^uint64(0) \|\| limit == 0) {
	// Some tools may introduce a fake mapping that spans the entire
	// address space. Assume that the address has already been
	// adjusted, so no additional base adjustment is necessary.
	return 0, nil
	}

	switch fh.Type {
	case elf.ET_EXEC:
	if loadSegment == nil {
	// Fixed-address executable, no adjustment.
	return 0, nil
	}
	if start == 0 && limit != 0 {
	// ChromeOS remaps its kernel to 0. Nothing else should come
	// down this path. Empirical values:
	// VADDR=0xffffffff80200000
	// stextOffset=0xffffffff80200198
	if stextOffset != nil {
	return -*stextOffset, nil
	}
	return -loadSegment.Vaddr, nil
	}
	if loadSegment.Vaddr-loadSegment.Off == start-offset {
	return offset, nil
	}
	if loadSegment.Vaddr == start-offset {
	return offset, nil
	}
	if start >= loadSegment.Vaddr && limit > start && (offset == 0 \|\| offset == pageOffsetPpc64) {
	// Some kernels look like:
	// VADDR=0xffffffff80200000
	// stextOffset=0xffffffff80200198
	// Start=0xffffffff83200000
	// Limit=0xffffffff84200000
	// Offset=0 (0xc000000000000000 for PowerPC64)
	// So the base should be:
	if stextOffset != nil && (start%pageSize) == (*stextOffset%pageSize) {
	// perf uses the address of _stext as start. Some tools may
	// adjust for this before calling GetBase, in which case the the page
	// alignment should be different from that of stextOffset.
	return start - *stextOffset, nil
	}

	return start - loadSegment.Vaddr, nil
	} else if start%pageSize != 0 && stextOffset != nil && *stextOffset%pageSize == start%pageSize {
	// ChromeOS remaps its kernel to 0 + start%pageSize. Nothing
	// else should come down this path. Empirical values:
	// start=0x198 limit=0x2f9fffff offset=0
	// VADDR=0xffffffff81000000
	// stextOffset=0xffffffff81000198
	return -(*stextOffset - start), nil
	}

	return 0, fmt.Errorf("Don't know how to handle EXEC segment: %v start=0x%x limit=0x%x offset=0x%x", *loadSegment, start, limit, offset)
	case elf.ET_REL:
	if offset != 0 {
	return 0, fmt.Errorf("Don't know how to handle mapping.Offset")
	}
	return start, nil
	case elf.ET_DYN:
	// The process mapping information, start = start of virtual address range,
	// and offset = offset in the executable file of the start address, tells us
	// that a runtime virtual address x maps to a file offset
	// fx = x - start + offset.
	if loadSegment == nil {
	return start - offset, nil
	}
	// The program header, if not nil, indicates the offset in the file where
	// the executable segment is located (loadSegment.Off), and the base virtual
	// address where the first byte of the segment is loaded
	// (loadSegment.Vaddr). A file offset fx maps to a virtual (symbol) address
	// sx = fx - loadSegment.Off + loadSegment.Vaddr.
	//
	// Thus, a runtime virtual address x maps to a symbol address
	// sx = x - start + offset - loadSegment.Off + loadSegment.Vaddr.
	return start - offset + loadSegment.Off - loadSegment.Vaddr, nil
	}
	return 0, fmt.Errorf("Don't know how to handle FileHeader.Type %v", fh.Type)
	}