将ldd命令移植到Arm开发板

今天开发过程中要查看arm开发板上一个可执行文件的依赖库，调用ldd命令，发现板子上没有，就想移植一个过来，在网上查阅了资料发现ldd不是一个二进制可执行文件，而是一个shell脚本文件，注意依赖 ld-linux.*.so 这个动态库工作。移植方法也很简单，主要是三步：

1. 将ldd文件的首行解释器的定义改一下，“#! /bin/bash”改为“#! /bin/sh”。
2. 找到“RTLDLIST=***********”，这一行将里面的库文件名改为开发板上相应的库文件名。
   在开发板运行查找命令：

find / -name ld-linux*

我的开发板里的文件名是：ld-linux.so.3，故此行改为：RTLDLIST=“/lib/ld-linux.so.3”。

3. 下载到开发板的sbin目录中，运行。

发现运行查看版本都没问题，就是查看依赖库时报错：“ldd not a dynamic executable”。
百思不得其解，琢磨了半天，突然想到，这个ldd脚本是我从64位Diebian测试云服务器拷贝下来的，而Arm开发板是32位的，是不是这个原因？又上网搜索找了个32位Ubuntu的ldd脚本，改过之后，下载，测试，一切OK。这里记录一下过程，防止下次用到。
更改后的ldd脚本如下：

#! /bin/sh
# Copyright (C) 1996-2016 Free Software Foundation, Inc.
# This file is part of the GNU C Library.

# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.

# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# Lesser General Public License for more details.

# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# <http://www.gnu.org/licenses/>.


# This is the `ldd' command, which lists what shared libraries are
# used by given dynamically-linked executables.  It works by invoking the
# run-time dynamic linker as a command and setting the environment
# variable LD_TRACE_LOADED_OBJECTS to a non-empty value.

# We should be able to find the translation right at the beginning.
TEXTDOMAIN=libc
TEXTDOMAINDIR=/usr/share/locale

RTLDLIST="/lib/ld-linux.so.3"
warn=
bind_now=
verbose=

while test $# -gt 0; do
  case "$1" in
  --vers | --versi | --versio | --version)
    echo 'ldd (Ubuntu GLIBC 2.23-0ubuntu10) 2.23'
    printf $"Copyright (C) %s Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
" "2016"
    printf $"Written by %s and %s.
" "Roland McGrath" "Ulrich Drepper"
    exit 0
    ;;
  --h | --he | --hel | --help)
    echo $"Usage: ldd [OPTION]... FILE...
      --help              print this help and exit
      --version           print version information and exit
  -d, --data-relocs       process data relocations
  -r, --function-relocs   process data and function relocations
  -u, --unused            print unused direct dependencies
  -v, --verbose           print all information
"
    printf $"For bug reporting instructions, please see:\\n%s.\\n" \
      "<https://bugs.launchpad.net/ubuntu/+source/glibc/+bugs>"
    exit 0
    ;;
  -d | --d | --da | --dat | --data | --data- | --data-r | --data-re | \
  --data-rel | --data-relo | --data-reloc | --data-relocs)
    warn=yes
    shift
    ;;
  -r | --f | --fu | --fun | --func | --funct | --functi | --functio | \
  --function | --function- | --function-r | --function-re | --function-rel | \
  --function-relo | --function-reloc | --function-relocs)
    warn=yes
    bind_now=yes
    shift
    ;;
  -v | --verb | --verbo | --verbos | --verbose)
    verbose=yes
    shift
    ;;
  -u | --u | --un | --unu | --unus | --unuse | --unused)
    unused=yes
    shift
    ;;
  --v | --ve | --ver)
    echo >&2 $"ldd: option \`$1' is ambiguous"
    exit 1
    ;;
  --)		# Stop option processing.
    shift; break
    ;;
  -*)
    echo >&2 'ldd:' $"unrecognized option" "\`$1'"
    echo >&2 $"Try \`ldd --help' for more information."
    exit 1
    ;;
  *)
    break
    ;;
  esac
done

nonelf ()
{
  # Maybe extra code for non-ELF binaries.
  return 1;
}

add_env="LD_TRACE_LOADED_OBJECTS=1 LD_WARN=$warn LD_BIND_NOW=$bind_now"
add_env="$add_env LD_LIBRARY_VERSION=\$verify_out"
add_env="$add_env LD_VERBOSE=$verbose"
if test "$unused" = yes; then
  add_env="$add_env LD_DEBUG=\"$LD_DEBUG${LD_DEBUG:+,}unused\""
fi

# The following command substitution is needed to make ldd work in SELinux
# environments where the RTLD might not have permission to write to the
# terminal.  The extra "x" character prevents the shell from trimming trailing
# newlines from command substitution results.  This function is defined as a
# subshell compound list (using "(...)") to prevent parameter assignments from
# affecting the calling shell execution environment.
try_trace() (
  output=$(eval $add_env '"$@"' 2>&1; rc=$?; printf 'x'; exit $rc)
  rc=$?
  printf '%s' "${output%x}"
  return $rc
)

case $# in
0)
  echo >&2 'ldd:' $"missing file arguments"
  echo >&2 $"Try \`ldd --help' for more information."
  exit 1
  ;;
1)
  single_file=t
  ;;
*)
  single_file=f
  ;;
esac

result=0
for file do
  # We don't list the file name when there is only one.
  test $single_file = t || echo "${file}:"
  case $file in
  */*) :
       ;;
  *) file=./$file
     ;;
  esac
  if test ! -e "$file"; then
    echo "ldd: ${file}:" $"No such file or directory" >&2
    result=1
  elif test ! -f "$file"; then
    echo "ldd: ${file}:" $"not regular file" >&2
    result=1
  elif test -r "$file"; then
    RTLD=
    ret=1
    for rtld in ${RTLDLIST}; do
      if test -x $rtld; then
	dummy=`$rtld 2>&1` 
	if test $? = 127; then
	  verify_out=`${rtld} --verify "$file"`
	  ret=$?
	  case $ret in
	  [02]) RTLD=${rtld}; break;;
	  esac
	fi
      fi
    done
    case $ret in
    0|2)
      try_trace "$RTLD" "$file" || result=1
      ;;
    1)
      # This can be a non-ELF binary or no binary at all.
      nonelf "$file" || {
	echo $"	not a dynamic executable"
	result=1
      }
      ;;
    *)
      echo 'ldd:' ${RTLD} $"exited with unknown exit code" "($ret)" >&2
      exit 1
      ;;
    esac
  else
    echo 'ldd:' $"error: you do not have read permission for" "\`$file'" >&2
    result=1
  fi
done

exit $result
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