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- // Copyright 2018 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 symbol_inject
- import (
- "debug/elf"
- "fmt"
- "io"
- )
- type mockableElfFile interface {
- Symbols() ([]elf.Symbol, error)
- Sections() []elf.SectionHeader
- Type() elf.Type
- }
- var _ mockableElfFile = elfFileWrapper{}
- type elfFileWrapper struct {
- *elf.File
- }
- func (f elfFileWrapper) Sections() []elf.SectionHeader {
- ret := make([]elf.SectionHeader, len(f.File.Sections))
- for i, section := range f.File.Sections {
- ret[i] = section.SectionHeader
- }
- return ret
- }
- func (f elfFileWrapper) Type() elf.Type {
- return f.File.Type
- }
- type mockElfFile struct {
- symbols []elf.Symbol
- sections []elf.SectionHeader
- t elf.Type
- }
- func (f mockElfFile) Sections() []elf.SectionHeader { return f.sections }
- func (f mockElfFile) Symbols() ([]elf.Symbol, error) { return f.symbols, nil }
- func (f mockElfFile) Type() elf.Type { return f.t }
- func elfSymbolsFromFile(r io.ReaderAt) (*File, error) {
- elfFile, err := elf.NewFile(r)
- if err != nil {
- return nil, cantParseError{err}
- }
- return extractElfSymbols(elfFileWrapper{elfFile})
- }
- func extractElfSymbols(elfFile mockableElfFile) (*File, error) {
- symbols, err := elfFile.Symbols()
- if err != nil {
- return nil, err
- }
- file := &File{}
- for _, section := range elfFile.Sections() {
- file.Sections = append(file.Sections, &Section{
- Name: section.Name,
- Addr: section.Addr,
- Offset: section.Offset,
- Size: section.Size,
- })
- }
- _ = elf.Section{}
- for _, symbol := range symbols {
- if elf.ST_TYPE(symbol.Info) != elf.STT_OBJECT {
- continue
- }
- if symbol.Section == elf.SHN_UNDEF || symbol.Section >= elf.SHN_LORESERVE {
- continue
- }
- if int(symbol.Section) >= len(file.Sections) {
- return nil, fmt.Errorf("invalid section index %d", symbol.Section)
- }
- section := file.Sections[symbol.Section]
- var addr uint64
- switch elfFile.Type() {
- case elf.ET_REL:
- // "In relocatable files, st_value holds a section offset for a defined symbol.
- // That is, st_value is an offset from the beginning of the section that st_shndx identifies."
- addr = symbol.Value
- case elf.ET_EXEC, elf.ET_DYN:
- // "In executable and shared object files, st_value holds a virtual address. To make these
- // files’ symbols more useful for the dynamic linker, the section offset (file interpretation)
- // gives way to a virtual address (memory interpretation) for which the section number is
- // irrelevant."
- if symbol.Value < section.Addr {
- return nil, fmt.Errorf("symbol starts before the start of its section")
- }
- addr = symbol.Value - section.Addr
- if addr+symbol.Size > section.Size {
- return nil, fmt.Errorf("symbol extends past the end of its section")
- }
- default:
- return nil, fmt.Errorf("unsupported elf file type %d", elfFile.Type())
- }
- file.Symbols = append(file.Symbols, &Symbol{
- Name: symbol.Name,
- Addr: addr,
- Size: symbol.Size,
- Section: section,
- })
- }
- return file, nil
- }
- func dumpElfSymbols(r io.ReaderAt) error {
- elfFile, err := elf.NewFile(r)
- if err != nil {
- return cantParseError{err}
- }
- symbols, err := elfFile.Symbols()
- if err != nil {
- return err
- }
- fmt.Println("mockElfFile{")
- fmt.Printf("\tt: %#v,\n", elfFile.Type)
- fmt.Println("\tsections: []elf.SectionHeader{")
- for _, section := range elfFile.Sections {
- fmt.Printf("\t\t%#v,\n", section.SectionHeader)
- }
- fmt.Println("\t},")
- fmt.Println("\tsymbols: []elf.Symbol{")
- for _, symbol := range symbols {
- fmt.Printf("\t\t%#v,\n", symbol)
- }
- fmt.Println("\t},")
- fmt.Println("}")
- return nil
- }
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