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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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