如何让 GDB 将我手工制作的可运行 ELF 文件识别为可执行文件？

Question

I have the following AMD64 ELF file on 64-bit (Arch)linux (not formatted to make it easier to copy-paste)

7F 45 4C 46 02 01 01 00 00 00 00 00 00 00 00 00 02 00 3E 00 01 00 00 00 78 00 40 00 00 00 00 00 40 00 00 00 00 00 00 00 84 00 00 00 00 00 00 00 00 00 00 00 40 00 38 00 01 00 40 00 03 00 02 00 01 00 00 00 05 00 00 00 78 00 00 00 00 00 00 00 78 00 40 00 00 00 00 00 00 00 00 00 00 00 00 00 0C 00 00 00 00 00 00 00 0C 00 00 00 00 00 00 00 00 00 20 00 00 00 00 00 48 B8 3C 00 00 00 00 00 00 00 0F 05 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 01 00 00 00 06 00 00 00 00 00 00 00 78 00 40 00 00 00 00 00 78 00 00 00 00 00 00 00 0C 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 08 00 00 00 00 00 00 00 0C 00 00 00 00 00 00 00 07 00 00 00 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 44 01 00 00 00 00 00 00 10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00 00 00 2E 74 65 78 74 00 2E 73 68 73 74 72 74 61 62 00

which does nothing but immediately exit.

The output of readelf -a is

ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x400078
  Start of program headers:          64 (bytes into file)
  Start of section headers:          132 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         1
  Size of section headers:           64 (bytes)
  Number of section headers:         3
  Section header string table index: 2

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .text             PROGBITS         0000000000400078  00000078
       000000000000000c  000000000000000c  AX       0     0     8
  [ 2] .shstrtab         STRTAB           0000000000000000  00000144
       0000000000000010  0000000000000010           0     0     0
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  l (large), p (processor specific)

There are no section groups in this file.

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000078 0x0000000000400078 0x0000000000000000
                 0x000000000000000c 0x000000000000000c  R E    0x200000

 Section to Segment mapping:
  Segment Sections...
   00     .text 

There is no dynamic section in this file.

There are no relocations in this file.

The decoding of unwind sections for machine type Advanced Micro Devices X86-64 is not currently supported.

No version information found in this file.

Although the executable runs perfectly fine, when I execute gdb <file> I am greeted with "0x7ffd7e078db0s": not in executable format: file format not recognized

The weird thing is, when I remove all sections (so an ELF remains with only file header, program header and code) GDB does recognize it as an executable.

Thus, my question is, how can I let GDB recognize my file as an executable? Alternatively, what information does GDB use to determine that a file is executable?

Thanks for your time and effort.

Answer 1

Your .shstrtab section has length 0x10 , but should have length 0x11 :

 0  1  2  3  4  5  6  7  8  9  A  B  C  D  E  F      <-- byte offset
\0  .  t  e  x  t \0  .  s  h  s  t  r  t  a  b  \0  <-- value

Changing 293 rd byte from 0x10 to 0x11 makes the program run under GDB.

PS eu-readelf is more robust than readelf , and makes the error clearer. Using original (broken) binary:

$ readelf -WS junk.elf
There are 3 section headers, starting at offset 0x84:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .text             PROGBITS        0000000000400078 000078 00000c 0c  AX  0   0  8
  [ 2] .shstrtab         STRTAB          0000000000000000 000144 000010 10      0   0  0

Compare to eu-readelf :

$ eu-readelf -WS junk.elf
There are 3 section headers, starting at offset 0x84:

Section Headers:
[Nr] Name                 Type         Addr             Off      Size     ES Flags Lk Inf Al
[ 0]                      NULL         0000000000000000 00000000 00000000  0        0   0  0
[ 1] .text                PROGBITS     0000000000400078 00000078 0000000c 12 AX     0   0  8
[ 2] <corrupt>            STRTAB       0000000000000000 00000144 00000010 16        0   0  0