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Accepted
Eric
Asked: 2015-10-23 08:32:06 +0800 CST

How can I get information about a binary file that won't execute?

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When I run one of my user's applications named "myfile". 

$ ./myfile

I receive the following output

bash: ./myfile: cannot execute binary file

My user expects the binary file to run. I assume this is a compilation error but am unable to confirm it. I ran the file command

$ file myfile
myfile: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped

My RHEL6 OS is 64-bit

$ uname -p -o
x86_64 GNU/Linux

So it looks to me like it was complied for the right architecture. I don't understand what "relocatable" means in the file command's output and was not able to get an explanation form the man pages.

For good measure I checked for Shared Library Dependencies

$ ldd myfile 
not a dynamic executable

Is there any way I can get this file to run or give my user some constructive information about why it won't run (such as he needs to recompile using x)?

Strace

$ strace ./myfile
execve("./myfile", ["./myfile"], [/* 22 vars */]) = -1 ENOEXEC (Exec format error)
dup(2)                                  = 3
fcntl(3, F_GETFL)                       = 0x8002 (flags O_RDWR|O_LARGEFILE)
fstat(3, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f7a9fc93000
lseek(3, 0, SEEK_CUR)                   = -1 ESPIPE (Illegal seek)
write(3, "strace: exec: Exec format error\n", 32strace: exec: Exec format error
) = 32
close(3)                                = 0
munmap(0x7f7a9fc93000, 4096)            = 0
exit_group(1)                           = ?

readelf output

readelf -S ./myfile    There are 13 section headers, starting at offset 0x1e8:

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         0000000000000000  00000040
       0000000000000098  0000000000000000  AX       0     0     4
  [ 2] .rela.text        RELA             0000000000000000  000006e0
       0000000000000120  0000000000000018          11     1     8
  [ 3] .data             PROGBITS         0000000000000000  000000d8
       0000000000000010  0000000000000000  WA       0     0     4
  [ 4] .bss              NOBITS           0000000000000000  000000e8
       0000000000000000  0000000000000000  WA       0     0     4
  [ 5] .rodata           PROGBITS         0000000000000000  000000e8
       0000000000000033  0000000000000000   A       0     0     1
  [ 6] .comment          PROGBITS         0000000000000000  0000011b
       000000000000002d  0000000000000001  MS       0     0     1
  [ 7] .note.GNU-stack   PROGBITS         0000000000000000  00000148
       0000000000000000  0000000000000000           0     0     1
  [ 8] .eh_frame         PROGBITS         0000000000000000  00000148
       0000000000000038  0000000000000000   A       0     0     8
  [ 9] .rela.eh_frame    RELA             0000000000000000  00000800
       0000000000000018  0000000000000018          11     8     8
  [10] .shstrtab         STRTAB           0000000000000000  00000180
       0000000000000061  0000000000000000           0     0     1
  [11] .symtab           SYMTAB           0000000000000000  00000528
       0000000000000180  0000000000000018          12     9     8
  [12] .strtab           STRTAB           0000000000000000  000006a8
       0000000000000037  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings)
  I (info), L (link order), G (group), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)
linux

1 Answers

  1. Best Answer

    It sounds like relocatable has to do with an object file that is not an executable.

    Executables should look like this

    ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=a8ff57737fe60fba639d91d603253f4cdc6eb9f7, stripped

    Object files look like this

    # file /usr/lib/x86_64-linux-gnu/crtn.o
/usr/lib/x86_64-linux-gnu/crtn.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped

    If needed, you can also get more information this way

    # objdump -x myfile

    Or disassemble

    # objdump -d myfile

    List symbols from a object file (not stripped)

    # nm /usr/lib/x86_64-linux-gnu/gcrt1.o
                 U atexit
0000000000000000 b called.4237
0000000000000000 D __data_start
0000000000000000 W data_start
                 U etext
0000000000000030 T __gmon_start__
0000000000000000 R _IO_stdin_used
                 U __libc_csu_fini
                 U __libc_csu_init
                 U __libc_start_main
                 U main
                 U _mcleanup
                 U __monstartup
0000000000000000 T _start

    Trying to list symbols from executable (stripped)

    # nm /bin/bash
nm: /bin/bash: no symbols
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