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/localeRTLDLIST="/lib/ld-linux.so.3"
warn=
bind_now=
verbose=while test $# -gt 0; docase "$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=yesshift;;-r | --f | --fu | --fun | --func | --funct | --functi | --functio | \--function | --function- | --function-r | --function-re | --function-rel | \--function-relo | --function-reloc | --function-relocs)warn=yesbind_now=yesshift;;-v | --verb | --verbo | --verbos | --verbose)verbose=yesshift;;-u | --u | --un | --unu | --unus | --unuse | --unused)unused=yesshift;;--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 $"Try \`ldd --help' for more information."exit 1;;*)break;;esac
donenonelf ()
{# Maybe extra code for non-ELF binaries.return 1;
}add_env="LD_TRACE_LOADED_OBJECTS=1 LD_WARN=$warn LD_BIND_NOW=$bind_now"
add_env="$add_env LD_LIBRARY_VERSION=\$verify_out"
add_env="$add_env LD_VERBOSE=$verbose"
if test "$unused" = yes; thenadd_env="$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;;
esacresult=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;;esacif test ! -e "$file"; thenecho "ldd: ${file}:" $"No such file or directory" >&2result=1elif test ! -f "$file"; thenecho "ldd: ${file}:" $"not regular file" >&2result=1elif test -r "$file"; thenRTLD=ret=1for rtld in ${RTLDLIST}; doif test -x $rtld; thendummy=`$rtld 2>&1` if test $? = 127; thenverify_out=`${rtld} --verify "$file"`ret=$?case $ret in[02]) RTLD=${rtld}; break;;esacfifidonecase $ret in0|2)try_trace "$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)" >&2exit 1;;esacelseecho 'ldd:' $"error: you do not have read permission for" "\`$file'" >&2result=1fi
doneexit $result
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