[Bug 1616609] Re: ldd reports incorrectly "not a dynamic executable" when the executable's loader is not present

[Igor Z]

I think that I got the same bug here:
https://askubuntu.com/questions/1097900/ldd-started-to-show-me-not-a
-dynamic-executable

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https://bugs.launchpad.net/bugs/1616609

Title:
  ldd reports incorrectly "not a dynamic executable" when the
  executable's loader is not present

Status in glibc package in Ubuntu:
  Confirmed

Bug description:
  system:Ubuntu 16.04.1 LTS
  Linux leno 4.4.0-34-generic #53-Ubuntu SMP Wed Jul 27 16:06:39 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
  package in use: libc-bin 2.23-0ubuntu3

  The ldd script comes with wired in paths for the 64 bit and 32 bit loaders, but other architectures
  are ignored.  On a 64 bit Ubuntu installation, the 32 bit loader is not present by default, so
  32 bit i386 dynamic executables are claimed to be "not a dynamic executable".  This is simply wrong.
  On a 64 bit Intel sytem, ldd is frequently used to identify missing necessary 32 bit libraries for
  32 bit executables, so their packages may be installed.
  It fails to do this unless ld-linux-x32.so.2 is present from the libc6-x32 package.

  A minimum fix would be to change the present message to:
   "not a dynamic executable or possibly a missing loader, like ld-linux-x32.so.2 from the libc6-x32 package." 

  A better fix would be to use a program which can handle any architecture ELF file to report the needed libraries. Default Ubuntu installations do contain programs like file, readelf, and objdump which can successfully read these ELF files without loaders being present.  The current ldd script even has a function, noelf, which might be better named "noloader" in which a fallback report may be issued to identify needed libraries. Using readelf in the "noloader" function, even different architectures may be correctly identified and their dependencies output.  Below is a sample diff/patch for ldd which produces useful output for dynamic ELF files 
  regardless of architecture:

  ====snip====
  97c97
  < nonelf ()
  ---
  > noloader ()
  99,100c99,105
  <   # Maybe extra code for non-ELF binaries.
  <   return 1;
  ---
  >   # Extra code for non-native architecture ELF binaries.
  >   [ "$verbose" == "yes" ] && echo "No loader present for file $1, trying other options."
  >   readelf -h $1 1>/dev/null 2>&1
  >   if [ $? -eq 0 ]; then
  >     readelf -h $1 | egrep "Class|Type|Machine"  &&   readelf -d $1 | grep NEEDED
  >   fi
  >   return $?
  173,174c178,179
  <       # This can be a non-ELF binary or no binary at all.
  <       nonelf "$file" || {
  ---
  >       # This can be an ELF with no loader present, a non-ELF binary or no binary at all.
  >       noloader "$file" || {
  ====snip===

  Comparison of original ldd with updated lddtest on three EFL files of different
  architecture and a text file. The host machine does have the i386 loader
  installed, but nothing for ARM.

  The files:
  $ file x y z txt
  x: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.3, for GNU/Linux 2.6.14, not stripped
  y: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.0.0, not stripped
  z: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=41cf4d8c7bbc4d37af0b7a55a7b0c48f8adfb2f5, not stripped
  txt: ASCII text

  The original ldd output:
  $ ldd x y z txt
  x:
      not a dynamic executable
  y:
      linux-gate.so.1 =>  (0xf777d000)
      libm.so.6 => /lib/i386-linux-gnu/libm.so.6 (0xf76fe000)
      libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xf7548000)
      /lib/ld-linux.so.2 (0x56633000)
  z:
      linux-vdso.so.1 =>  (0x00007fffc9dac000)
      libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f4f63531000)
      /lib64/ld-linux-x86-64.so.2 (0x0000557d89ab7000)
  txt:
      not a dynamic executable

  The patched ldd output (with the 386 loader present):
  $ ./lddtest x y z txt
  x:
    Class:                             ELF32
    Type:                              EXEC (Executable file)
    Machine:                           ARM
   0x00000001 (NEEDED)                     Shared library: [libdl.so.2]
   0x00000001 (NEEDED)                     Shared library: [libc.so.6]
  y:
      linux-gate.so.1 =>  (0xf774c000)
      libm.so.6 => /lib/i386-linux-gnu/libm.so.6 (0xf76cd000)
      libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xf7517000)
      /lib/ld-linux.so.2 (0x56644000)
  z:
      linux-vdso.so.1 =>  (0x00007ffe4388a000)
      libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f9550131000)
      /lib64/ld-linux-x86-64.so.2 (0x000056018c00d000)
  txt:
      not a dynamic executable

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