github.com/kubearmor/cilium@v1.6.12/pkg/alignchecker/elf.go

// Copyright (c) 2009 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//    * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//    * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//    * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

package alignchecker

import (
	"bytes"
	"compress/zlib"
	"debug/dwarf"
	"debug/elf"
	"encoding/binary"
	"fmt"
	"io"
	"strings"
)

// Adopted from elf.File.DWARF
// https://github.com/golang/go/blob/master/src/debug/elf/file.go (go1.11.2).
//
// The former method function tries to apply relocations when extracting DWARF
// debug sections. Unfortunately, the relocations are not implemented for EM_BPF,
// so the method fails.
//
// For struct alignment checks, no relocations are needed, so we comment out
// the relocation bits.
//
// NOTE: DO NOT USE THE FUNCTION FOR ANYTHING ELSE!
func getDWARFFromELF(f *elf.File) (*dwarf.Data, error) {
	dwarfSuffix := func(s *elf.Section) string {
		switch {
		case strings.HasPrefix(s.Name, ".debug_"):
			return s.Name[7:]
		case strings.HasPrefix(s.Name, ".zdebug_"):
			return s.Name[8:]
		default:
			return ""
		}

	}
	// sectionData gets the data for s, checks its size, and
	// applies any applicable relations.
	sectionData := func(i int, s *elf.Section) ([]byte, error) {
		b, err := s.Data()
		if err != nil && uint64(len(b)) < s.Size {
			return nil, err
		}

		if len(b) >= 12 && string(b[:4]) == "ZLIB" {
			dlen := binary.BigEndian.Uint64(b[4:12])
			dbuf := make([]byte, dlen)
			r, err := zlib.NewReader(bytes.NewBuffer(b[12:]))
			if err != nil {
				return nil, err
			}
			if _, err := io.ReadFull(r, dbuf); err != nil {
				return nil, err
			}
			if err := r.Close(); err != nil {
				return nil, err
			}
			b = dbuf
		}

		for _, r := range f.Sections {
			if r.Type != elf.SHT_RELA && r.Type != elf.SHT_REL {
				continue
			}
			if int(r.Info) != i {
				continue
			}
			//rd, err := r.Data()
			_, err := r.Data()
			if err != nil {
				return nil, err
			}
			// err = f.applyRelocations(b, rd)
			// if err != nil {
			// 	return nil, err
			// }
		}
		return b, nil
	}

	// There are many other DWARF sections, but these
	// are the ones the debug/dwarf package uses.
	// Don't bother loading others.
	var dat = map[string][]byte{"abbrev": nil, "info": nil, "str": nil, "line": nil, "ranges": nil}
	for i, s := range f.Sections {
		suffix := dwarfSuffix(s)
		if suffix == "" {
			continue
		}
		if _, ok := dat[suffix]; !ok {
			continue
		}
		b, err := sectionData(i, s)
		if err != nil {
			return nil, err
		}
		dat[suffix] = b
	}

	d, err := dwarf.New(dat["abbrev"], nil, nil, dat["info"], dat["line"], nil, dat["ranges"], dat["str"])
	if err != nil {
		return nil, err
	}

	// Look for DWARF4 .debug_types sections.
	for i, s := range f.Sections {
		suffix := dwarfSuffix(s)
		if suffix != "types" {
			continue
		}

		b, err := sectionData(i, s)
		if err != nil {
			return nil, err
		}

		err = d.AddTypes(fmt.Sprintf("types-%d", i), b)
		if err != nil {
			return nil, err
		}
	}

	return d, nil
}